by Julia Galef

One of the most iconic symbols of evolution—the tree of life (left), a visual metaphor for the branching ancestry of species—has recently become one of its most controversial. The idea of a tree dates back to Charles Darwin himself. In January, a cover of New Scientist featured the tree emblazoned with the words "Darwin was Wrong," referring to the past decade's discoveries that single-celled organisms exchange genetic material in ways other than reproduction. Some scientists have suggested that this process, called lateral gene transfer, makes our tree of life really more of a "web of life."

That New Scientist cover made repeated appearances at the University of Chicago's 29-31 October "Darwin 2009" conference, where multiple speakers agreed that whatever the extent of lateral gene transfer, it's not enough to obscure the overall treelike shape of evolution. "If the history of bacteria and eukarya were really a web, then the enterprise of finding a tree would fail, but it hasn't," said entomologist Philip Ward of the University of California, Davis. New research supports his case, including a forthcoming Nature paper by Martin Wu et al. that will show tree-based selection to be an effective way of identifying novel protein families, indicating that lateral gene transfer has likely redistributed genes only among closely related branches.

However, anti-Darwinians have seized on this controversy as prime ammunition in their attacks on evolution itself. "The creationists will drive you nuts—they'll take this controversy to say there's no universal common ancestry, therefore there's no tree, therefore there's no evolution," said Eugenie Scott, executive director of the National Center for Science Education. Ironically, as Scott and other speakers pointed out, even as creationists claim the tree of life is dead, they have simultaneously adopted the model for themselves: Current dogma touts a "Creationist Orchard" of many separate trees, each with a trunk representing one of Noah's pairs of passengers.

Credit: Wikimedia Commons

by Julia Galef

CHICAGO, ILLINOIS—The birthplace of modern evolutionary biology can arguably be located at a landmark 1959 conference at the University of Chicago, which synthesized the then-new discoveries of DNA and genetics with Charles Darwin's observations on evolution. Last weekend, the university reprised that famous meeting with a "Darwin 2009" conference (right) that highlighted just how much has changed in the past 50 years: Dizzying genetic and genomic advances are allowing us to answer questions our 1959 counterparts couldn't even have dreamed of asking.

For instance, only recently have scientists begun to suspect that much of evolutionary change might be due not to mutations in the familiar protein-coding DNA but to other, noncoding DNA that regulates how and where the coding DNA expresses itself. The role of noncoding DNA in evolution has been hotly debated by scientists, but even as recently as last year the evidence was still spotty.

That's why one talk at the 29 to 31 October conference set off a particularly excited wave of coffee-break chatter: Stanford University evolutionary biologist David Kingsley revealed new results demonstrating how a change in the regulatory DNA of a single gene can produce a dramatic, adaptive change in an animal's anatomy.

Stickleback fish originated in marine environments, where they evolved a pelvis that protected them against predators by pushing out its spines, turning them into prickly, swimming pincushions (left). Over time, however, many stickleback populations spread to neighboring freshwater regions, where their pelvises were suddenly a disadvantage. In place of their traditional predators, they now faced large carnivorous insects like dragonflies who used the sticklebacks' prominent spines to nab them as they swam in shallow waters. So stickleback populations in freshwater began to lose their pelvises, a classic adaptive trick that Darwin himself could have appreciated; Kingsley's team wanted to know how, exactly, the sticklebacks' genes pulled it off.

Several years ago, Kingsley traced the loss of the pelvis back to a single gene called Pitx1.  Because the coding DNA in that gene was present in both the marine and freshwater sticklebacks, he reasoned that some part of Pitx1's noncoding DNA must be regulating the gene's expression, producing pelvises in the marine fish and none in the freshwater fish. Although his hypothesis made a big splash upon its publication (and has been widely cited since) it was still just a hypothesis, until this year.

After testing piece after piece of noncoding DNA from the spiny marine sticklebacks, Kingsley's team zeroed in on a sequence that seemed to correspond to pelvic development. So they cloned that sequence from the marine fish and injected it into the embryos of freshwater fish in order to produce the phenotype of a marine fish, a feat rarely attempted, let alone accomplished, in live animals. Sure enough, the resulting sticklebacks developed pelvises.

It's a particularly striking piece of evidence for the regulatory gene hypothesis, in part because the anatomical change is so large. "Losing an entire limb is the kind of dramatic change you usually see between only distantly related species," Kingsley said, so to produce such an effect from a single regulatory sequence of one gene is a bombshell. His results are also remarkable for including multiple, independent lineages of stickleback, addressing another hot topic in evolutionary biology: Do organisms exposed to the same selective pressures use the same genetic mechanism to adapt? Kingsley's results suggest that, at least in some cases, they do.

"The Holy Grail of research on adaptation is to identify adaptive mechanisms, the traits that contributed to adaptation and the genetic basis of adaptive traits," evolutionary biologist Doug Schemske of Michigan State University in East Lansing said after the conference. "Most of us can at best answer one of these questions—Kingsley has done it all."

Photo credits: Lucas Canino (conference); Frank Chan (marine stickleback)

 by Elizabeth Pennisi

Why in tropical forests do tall broad-leaf trees tower over a layer of understory species? What dictates that shrubs and herbaceous plants pepper the ground below, creating an environment recognizable the world over as tropical forest.

Biologists have long wanted to know why forests and other ecological communities look the way they do. In the beginning of the 19th century, Prussian naturalist Alexander von Humboldt started to find out. He assembled the first comprehensive treatise on how vegetation varies with altitude, climate, soil, and other factors. The work was a groundbreaking exploration of the physical underpinnings of ecological structure: what determines the species that make up a community and their relative abundance.

More than a half-century later, Charles Darwin quietly conducted experiments in his garden at Down House that were even more seminal. Examining a patch of unkempt lawn as it went to seed, Darwin observed that the species changed through time and that competition led to the demise of less-vigorous ones.

Ever since, ecologists have wrestled with understanding what dictates the proportions of each plant in communities varying from meadows to montane forests. How these forces set up communities has "arguably been one of the most primary questions driving ecological science since its origins," says Brian Enquist of the University of Arizona, Tucson. Competition, predation, disturbance, and other factors have a heavy hand, and new research is showing the influential role of evolution, as well.

In this month's Origins essay, Erik Stokstad explores the thinking that has gone into understanding and interpreting community compositions. A combination of physical and biological forces organizes species into predictable communities such that a rainforest is recognizable no matter what part of the planet it grows in. He describes the role of these physical factors and the influence of different biological interactions. Some ecologists think competition is key; others contend the abundance and diversity of species in a community is determined mainly by random dispersal, speciation, and extinction. This latter idea, dubbed the "Unified Neutral Theory of Biodiversity," makes a radical assumption: It considers all organisms of the same trophic level (plants, say, or herbivores) as demographically identical; that is, each organism in a particular level has about the same chance of reproducing, dying, migrating, or giving rise to a new species. The neutral theory has had mixed support. Some researchers think that biological interactions and “neutral” factors work in concert. As challenging as sorting out the rules that govern ecological structure has been, the effort is worth it, say researchers, because of the potential conservation benefit.

Image: Katharine Sutliff

 by Elizabeth Pennisi

As social as humans are, their cooperative nature pales in comparison to that of ants, bees, wasps, and termites (see hill, left). Colonies of these insects can number in the millions and function seamlessly as “superorganisms.” In their book, The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies, Burt Hölldobler and E. O. Wilson point out that this way of life makes for very successful living. These insects represent a mere 2% of the insect species yet take up two-thirds of the insect biomass. In tropical rainforests, ants outweigh all the mammals and land vertebrates combined.

Yet the scores of entomologists and evolutionary biologists who have marveled at the efficiency of superorganisms have yet to sort out for sure how superorganisms evolved. True superorganisms are highly eusocial: Typically, one or a few queens lay all the eggs, which are tended to by nonreproductive workers. Their fecundity can be astonishing: In their more than 10-year life span, queens of Atta ants (see right) can produce 150 million daughters, for example. Multiple generations live together; and because workers are sterile, very few conflicts arise, and the colony runs quite efficiently.

Less extreme versions of this lifestyle exist, leading some to suggest that eusociality evolved in stages, starting with a female that set up communal nests with other females, with some forgoing reproduction to help provision and protect the young. A few have suggested that it’s not even that critical that the founding females be all that closely related.

In my Origins essay on cooperation, I  did not touch upon the origin of these truly social insects. But Jacobus Boomsma of the University of Copenhagen, Denmark, has thought extensively about this question and rejects the stepwise progression from cooperative breeding to eusociality, asserting that not just close kinship but also lifetime monogamy is critical to incipient eusociality. Early eusocial species “have a very special form of strict monogamy that has been unappreciated,” he says. This idea has been suggested before, but “Boomsma has performed a valuable service in reviving it and extending it,” says Andrew Bourke of the University of East Anglia, United Kingdom.

Termites mate for life, with a single queen and “king” producing generations of siblings, all equally related to one another. Once in their lifetime, wasps, bees, and ants leave the nest on a mating frenzy, with the queens returning with enough sperm to last the rest of their reproductive years. The consequence of having just one mate for life is that the many generations of offspring are all siblings that on average share half their genes. That number of genes in common is the same as they would have in common with their own offspring should they try to reproduce. Thus, if there is even a small survival advantage to group living, that advantage would be a strong enough selective force to encourage the evolution of sterile castes and true eusociality, Boomsma argues. “When a parent refrains from mating with any additional mates, their offspring are free to stop mating at all,” he explains. However, strict monogamy is rare, particularly over evolutionary time scales, and thus, so is eusociality.

In the late 1950s, Kansas University entomologist Charles Michener suggested that eusociality could arise in one of two ways. By the subsocial route, parents associated with offspring; by the parasocial or semisocial route, females joined forces with their peers in communal settings. Yet even today, that latter scenario lacks any hard evidence, says Boomsma. Such cooperative breeding setups never lead to permanently sterile helper castes; there are too many conflicts of interest. Those conflicts disappear where queens have a brief mating interval and then settle down for a life of reproduction using the sperm acquired during that one fling.

A 2008 phylogenetic analysis of mating systems in ants, bees, wasps, and termites supports Boomsma’s hypothesis. In 2008, William Hughes of the University of Leeds, U.K., and his colleagues looked deep into the past of 267 eusocial bees, wasps, and ants. They found ancestors of these lineages of eusocial insects were monogamous. Only later, once sterile castes had evolved, have some groups begun to mate more than once they reported.

To hear more about Boomsma’s hypothesis, listen to a talk he gave earlier this year at the Evolution of Society meeting sponsored by the Royal Society.

 

Credits: (termite hill) Summi; Atta ants: Adrian Pingstone

by Elizabeth Pennisi

In my essay, On the Origin of Cooperation, I describe experiments in which people are asked to play computer games that help reveal our cooperative tendencies, and I discuss other studies involving the use of microbes to get at the basic principles of working together. But Laurent Keller has gone a step further to work out details of social interactions. An evolutionary biologist at the University of Lausanne, Switzerland, Keller and his colleagues use evolving robots in experiments looking at the evolution of communication, an essential and complex ingredient of cooperation. The robots help him address questions that cannot be addressed through his studies of ants.

The 15-centimeter-diameter robots (see left) can move in all four directions, like tanks, and are rimmed with LEDs that can emit blue light either randomly or under control of a neural network, depending on the experiment. Each has an omnidirectional camera that sees red and blue light, as well as downward-facing infrared sensors that can distinguish gray from black. The robots are tasked with finding “food,” which emits red light. “Poison” also emits red light and can be distinguished only from up close, when the infrared sensors are able to detect a black paper circle under the poison—the food sits on a gray circle. As the experiments begin, robots flash blue when they find food, a signal others can tap into to locate the food as well

The robots have “brains” and “genomes.” The brains are the software running on onboard computers, with neural networks consisting of 10 “sensory neurons" that convey what the camera and sensors perceive to “activation neurons" that make the motors turn and that light up the LEDs. There are 33 connections in all, with different strengths, each determined by a “gene.”

The researchers tested 100 colonies, each with 10 robots, in a 300-square-centimeter arena with food at one end and poison at the other. (See movie.) The robots got points for detecting and staying by food or lost points for targeting poison. Not everyone could fit by the food, so there was some jostling for position.

Using that system, the researchers scored each robot’s fitness and took the average of the colony's members to assess the colony’s fitness. Depending on the specific test, the researchers selected a subset of the best robots or the best colonies, tweaked their "genes," and ran the experiments again—up to 500 generations' worth. In some cases, they created groups of “related” robots—all with the same “brains”—to assess the affect of kinship on the social dynamics. They wanted to know what behaviors evolved when competition for food was between relatives versus between nonrelatives.

Over time, robots evolved when and where they emitted blue light, and they came to associate high-blue-light areas with food. Foraging efficiency increased, particularly in the highly related robots chosen from the best colonies, Keller and his colleagues reported in 2007. “Reliable communication evolves either when individuals in a group are highly related or when there is increased competition between groups, and so reduced competition between individuals,” explains Keller’s collaborator Sara Mitri.

In a second series of experiments, the researchers focused on “unrelated” robots selected for their individual fitness. Cooperation theory suggests that unrelated individuals have less motivation to share information and thus “one would expect unreliable communication to evolve,” Mitri explains. After 52 generations, the robots were much less likely to emit blue light by food and instead tended to light up around the poison, Keller and colleagues reported 15 September in the Proceedings of the National Academy of Sciences.

But the researchers also discovered that some robots continued to light up at the food source, even after 500 generations. It seems that once the meaning of the blue light became ambiguous, few enough robots were attracted that competition for food diminished to the point that there was little selection against having the blue light on at the food source, they reported. The net result: individual variation in light production and responses, says Keller. That parallels what is seen in animals: variable communication strategies.

The robots are allowing us to address questions that cannot be answered with real organisms, says Keller. With respect to the evolution of communication, “there are no fossils allowing us to study how it evolved, and it is not really amenable to experimental evolution.”

Photo credit: Sara Mitri and Walter Karlen

Movie credit: Stéphane Magnenat, Matthieu Bontemps, and Kevin Frugier.

In late January, New York-based internet consultant Phil Terry made a pitch on Facebook for members to post a Happy Birthday Darwin message. By 12 February, more than 200,000 members had signed on, far exceeding his expectations, he said. Since then, he's been shooting to make an even bigger splash. The goal is to have 1 million Facebook members by 24 November celebrating the 150th anniversary of the publication of Darwin's seminal book, On the Origin of Species.

Within a week of setting up the Facebook campaign, Terry started a Web site, Darwin150, complete with Tweets. Self-described as a "grassroots and scrappy" initiative "with a sense of humor,"  the project is run by volunteers with no funding other than in-kind contributions from organizations such as National Geographic. Yet it has set up a lecture series that will be webcast live. The series begins 16 September and runs through 24 November, with speakers that include Harvard University's E.O. Wilson and other biology luminaries.

"This series is unique in both the medium and the audience," says evolutionary biologist and author Sean Carroll of the University of Wisconsin, Madison, who has been active in Darwin celebrations across the globe and is involved in making a TV documentary on evolution. "It will be interesting to see its reach and the make-up of the audience."

Right now, the Facebook campaign is 750,000 members short. But, says So Young Park, head of the volunteer marketing team, "We are confident that we'll make our goal" and are expecting exponential growth in the days leading up to the anniversary. Go here to join.

—Elizabeth Pennisi

Image: The Darwin 150 Project

 

Cooperation has created a conundrum for generations of evolutionary scientists. If natural selection among individuals favors the survival of the fittest, why would one individual help another at a cost to itself? And yet cooperation and sacrifice are rampant in nature. Humans working together have transformed the planet to meet the needs of billions of people. Countless examples of cooperation between species exist as well. In this month's Origins essay, I examine our current understanding of this conundrum.

Cooperation has played a key role in evolutionary transitions, helping to create integrated systems. Worker ants have no offspring of their own and feed their queen’s offspring instead in colonies often considered “superorganisms” many thousands of individuals strong. Cells managed to specialize and stay together, giving rise to multicellular organisms. In both cases, formerly independent reproductive units become integrated into a single reproductive unit that became the target of selection.

The challenge of cooperation is to explain how self-interest is overcome, given the way natural selection works. Darwin suggested that selection might favor families whose members were cooperative, and researchers today agree that kinship helps explain cooperation. But cheaters—those who benefit without making sacrifices—are likely to evolve because they will have an edge over individuals that spend energy on helping others, thus threatening the stability of any cooperative venture. That puzzle has inspired biologists, mathematicians, even economists to come up with ways to explain how cooperation can arise and thrive. The essay examines how researchers have spent countless hours observing social organisms ranging from man to microbes. Humans are a particularly interesting case, as they cooperate with strangers, forgoing the genetic benefit derived from helping relatives. Yet even single-cell organisms have sophisticated means of working together. The study of both is helping to clarify the origin of this particularly important behavior.

—Elizabeth Pennisi

Illustration credit: Katharine Sutliff/Science

Two studies in the past month, one out yesterday, have rekindled the debate about where, when, and how often wolves were domesticated into canine companions. Check out a story yesterday by Elizabeth Pennisi about the latest suggestion that the first dogs came from China, 16,000 years ago. Already, the paper has some staunch critics.

 

Animals owe their survival to plants and other photosynthetic organisms. But according to a study published last week in Nature, photosynthesizers gave early animals another big assist, unleashing the Cambrian explosion, the big bang of animal evolution, 540 million years ago. The paper asserts that late in the Precambrian—the time before the Cambrian period—plants and other photosynthesizers settled the land, triggering a rise in atmospheric oxygen that shifted animal evolution into overdrive.

The Cambrian explosion was a burst of evolutionary creativity during which most of the modern groups of animals, such as arthropods, made their debuts. Anomalocaris (left) was one of the animals that swam the seas at the time. Scientists have ascribed the period's rapid diversification to everything from continental drift to the end of a global deep freeze.

Geochemist L. Paul Knauth of Arizona State University, Tempe, and geologist Martin Kennedy of the University of California, Riverside, posited a botanical explanation after analyzing the abundance of two rare isotopes, oxygen-18 and carbon-13. During the Precambrian, the key events took place in shallow seas, where limestone was forming. Sea level ups and downs mean that runoff from land sometimes infiltrates nascent rocks and changes their isotope balance—fresh water tends to be richer in carbon-12 derived from organic matter and lower in oxygen-18.

To check for signs of this freshwater infusion, Knauth and Kennedy pored over all published records of carbon and oxygen isotope measurements, plotting the relative ratios of carbon-13 and oxygen-18 against each other. They found that values for rocks from late in the Precambrian clustered with those for more recent rocks, which researchers know have been invaded by runoff laden with organic matter. That correspondence suggests that the land was lush during the late Precambrian. What Knauth and Kennedy term the “Precambrian greening” probably was under way by about 850 million years ago, the paper suggests. The identity of the early landlubbers is still uncertain, the most likely candidates being protists and small plants such as mosses and liverworts.

That leaves one step: explaining how the colonization of land by photosynthetic organisms started the diversification of marine animals that occurred between about 540 million and 490 million years ago. As Knauth and Kennedy see it, terrestrial greening would hasten erosion and further enhance growth of photosynthesizers, leading to an increase in the amount of carbon buried in sediments on land and in the sea. In turn, this decline in readily available carbon would allow atmospheric levels of oxygen to surge, permitting the evolution of larger, more complex animals.

—Mitch Leslie

Credit: Arthur Weasley, Wikimedia Commons

Toadstools, people, plants, and amoebae have strikingly similar cells. All these organisms keep their DNA coiled up in a nucleus. Their genes are interspersed with chunks of DNA that cells have to edit out to make proteins. Those proteins are shuttled through a maze of membranes before they can float out into the cell. And these cells all manufacture fuel in compartments called mitochondria.

All species with this arrangement are known as eukaryotes. The word is Greek for “true kernel,” referring to the nucleus. All other living things that lack a nucleus and mitochondria are known as prokaryotes. “It’s the deepest divide in the living world,” says William Martin of the University of Düsseldorf in Germany.

In this month’s Origins essay, Carl Zimmer looks at the evolution of the eukaryotic cell, one of the most important transitions in the history of life. Indeed, when you look at the natural world, most of what you see are these “true kernel” organisms.

Much of what we have learned about eukaryotes comes from studying their cell biology and their genomes. Through these efforts, researchers have made tremendous advances in the past 20 years in understanding that eukaryotes represent the merging of primitive microbes from both the archaeal and the bacterial worlds.

In addition to the essay, Zimmer talks about eukaryotes in a podcast.

—Elizabeth Pennisi

Image: Katharine Sutliff

Charles Darwin’s book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life contained his first thoughts on evolution. Now, 150 years later, computer scientist Greg McInerny is turning the idea on its head, drawing diagrams showing the “evolution” of the book as new editions were published. In the editing process, certain sections became “extinct,” that is, did not make it to the next edition. Other, stronger sections avoided the editor’s chopping block to make it into the final sixth edition—a kind of survival of the sentences—and in some cases, entirely new sections of text were added.

Together with London-based visual artist Stefanie Posavec, McInerny has devised the (En)tangled Word Bank, which shows the construction and evolution of the book. In some cases, the editions varied quite a bit, says McInerny, who is based at Microsoft Research in Cambridge in the United Kingdom. “For the second edition, Charles Darwin wanted a more popular and available version,” he says, so Darwin inserted references to a creator who may have been behind the initial creation of life. In the sixth edition, he added a whole new chapter discussing the support and criticism that had surrounded the book.

The diagram (left) represents the fifth edition. In it, the rim consists of four layers. The outer ring represents sentences; the next ring in signifies paragraphs, then subchapters and chapters follow. The central branching design represents the same divisions, with chapters at the base and sentences at the tips. The green “leaflets” show sentences that have “survived” multiple editions, and orange “leaflets” represent those that are “dying” and will be absent from the next edition. The darker the green or orange, the longer that sentence has survived through multiple editions.

(En)tangled Word Bank is an example of a “literary organism,” a structure devised by Posavec to show visually how books are constructed from their basic units. Her first such work was based on Jack Kerouac’s novel On the Road.

—Claire Thomas

Diagram: Greg McInerny and Stefanie Posavec

The nervous systems of modern animals are amazingly diverse. A few hundred nerve cells are all a lowly nematode needs to find food and a mate. With about 100,000 neurons, a fruit fly can perform aerial acrobatics, dance to woo a mate, and throw kicks and punches to repel a rival. The sperm whale’s 8-kilogram brain, the largest on the planet, is the navigation system for cross-ocean travel and 1000-meter dives and enables these highly social creatures to communicate. The human brain—one-sixth that size—is the wellspring of art, literature, and scientific inquiry.

In this month's Origins essay, Greg Miller takes a look at how nervous systems got started. He investigates what the first neurons might have looked like and what advantages they conferred on the animals that possessed them. These were questions the father of evolution, Charles Darwin, was ill-equipped to address. Only around the time Darwin died in 1882 were scientists beginning to develop stains to label individual cells for detailed postmortem neuroanatomical studies. Methods for investigating the electrical properties of individual neurons in living brain tissue were still decades away, to say nothing of techniques for investigating genes and genomes. Using such modern tools, scientists have recently begun to gain some tantalizing clues about the evolutionary origins of nervous systems. By looking down the tree of life, they are concluding that assembling these components into a cell a modern neuroscientist would recognize as a neuron probably happened very early in animal evolution, more than 600 million years ago. Most scientists agree that circuits of interconnected neurons probably arose soon thereafter, first as diffuse webs and later as a centralized brain and nerves. But the resolution on this picture is fuzzy. The order in which early branches split off the animal tree of life is controversial. And Miller takes a look at the different story lines implied by these different arrangements.

—Elizabeth Pennisi

Illustration: Katharine Sutliff

The latest survey to take the pulse of the public debate on evolution suggests that a majority of people see nothing wrong with believing in a god and accepting Charles Darwin's work.

The survey, presented yesterday at the World Conference of Science Journalists in London by the British Council as part of its international program Darwin Now, asked more than 10,000 adults across Argentina, China, Egypt, India, Mexico, Russia, South Africa, Spain, Great Britain, and the United States about their knowledge and acceptance of Darwin's theory of evolution. Across all countries, 70% of the adults surveyed felt somewhat familiar with Darwin and his work, with the highest levels of awareness being found in the United States and the United Kingdom (71% in both), Mexico (68%), and Argentina (65%). Seventy-three percent of the adults surveyed in South Africa and 62% in Egypt had never heard of Charles Darwin or of his theory of evolution, however.

Overall, knowing meant believing in evolution. Fifty-six percent of the people in all 10 countries who had heard of Darwin believed there is sufficient scientific evidence in support of Darwin's theory of evolution. A more detailed analysis, however, revealed a complex picture. Although the majority of adults surveyed in India (77%), China (72%), Mexico (65%), the United Kingdom (62%), Spain (61%), and Argentina (57%) accepted the theory of evolution as scientifically founded, only 48% did so in Russia, 42% in South Africa, 41% in the United States, and 25% in Egypt.

Acceptance of Darwin's theory of evolution didn't necessarily correlate with a rejection of creationism. The three countries with the greatest proportion of people (43%) believing that life on Earth was created by a god and has always existed in its current form were the United States, South Africa, and India.

The country that showed greatest support for the idea that evolution without a God guided the development of all life was China (67%), followed by Mexico (42%), the United Kingdom and Spain (38%), Argentina (37%), and Russia (32%). In Egypt, however, half of the adults surveyed believed in the evolution of human life in a process guided by a god.

"Most encouraging was a diversity in perspectives internationally," said Fern Elsdon-Baker, head of the British Council Darwin Now program, at yesterday's press conference.

"We need to look into these cultural differences. It gives an indication of how to target our efforts in public engagement across countries" when it comes to talking about Darwin and evolution, added Peter Kjaergaard, a historian at the Leverhulme Centre for Human Evolutionary Studies in Cambridge, U.K.

In spite of the cultural differences, what could be found in all of the 10 countries was acceptance of evolution and religion. In India, 85% of the adults surveyed saw nothing wrong with both believing in a god and accepting Darwin's theory of evolution. The same pattern was found in Mexico (65%), Argentina (62%), the United Kingdom, South Africa, and Russia (54%), the United States (53%), Spain (46%), Egypt (45%), and China (39%).

These were "quite surprising results," Elsdon-Baker said. There is "not necessarily a dichotomy." This contrasts with previous studies and media reports in which a conflict between religious beliefs and evolution views is assumed from the start, Kjaergaard added. The representation of the debate in newspapers "doesn't fit the general picture of the population throughout the world," he said.

—Elisabeth Pain

Charles Darwin’s theory of evolution certainly transformed the way we view life on Earth. Brian Regal (left) thinks it also had an impact on mythical creatures. Regal, a science historian at Kean University in Union, New Jersey, says that with the publication of On the Origin of Species, canine-man hybrids went out of fashion, making way for new beasts that embodied Darwin’s thinking: ape-men such as Bigfoot (a.k.a. Sasquatch) and the Yeti (a.k.a the Abominable Snowman). I spoke to Regal about how his study of the history of evolutionary theory led him to monsters and eventually to monster hunting.

Q: How did Darwin kill the werewolves?
B.R.: There were already writers in learned circles questioning the concept of the werewolf in the late 1500s. From an evolutionary point of view, the werewolf makes no sense. A half-human half-wolf/dog composite doesn’t work. An ape-man, however, a Bigfoot, makes sense because the ape-man idea is [at] the heart of human evolution. If you look at all the “wild man” stories in various cultures around the world, none of them mentions apes prior to the mid-19th century and the public debate brought on by Darwin's On the Origin of Species (1859) and T. H. Huxley's Man's Place in Nature (1863). This was the key to my idea. The “wild man” and the “ape” did not join forces to become the ape-man until after Darwin.

Q: How do you think Darwin viewed werewolves, centaurs, and other half-man, half-animal creatures?
B.R.: I have checked Darwin’s correspondence and published works, and I have not found him [to] make any direct reference to werewolves. In a letter from Darwin to the naturalist G. R. Waterhouse, dated 3 or 17 December 1843, he does mention that he did not believe there can be half of one thing and half of another. He also called animal monsters "a nasty, curious subject” when addressing a new book he had read by the French naturalist Saint-Hilaire.

Q: We often hear about people who have claimed to have seen Bigfoot, or the Yeti, or Sasquatch. Could they exist today?
B.R.: Peter Byrne, one of the grand old men of Bigfoot hunting, said it well. He said the way we will probably find out these creatures are real is when one of those giant 18-wheel logging trucks from the Pacific Northwest pulls into a roadside diner with a Bigfoot splattered all over the front grill. All my Bigfoot friends will get mad at this, but I think in the end they probably do not exist.

Q: You say that Darwin’s theory has caused us to shift our focus to ape-man hybrids. But recently in pop culture, creatures like Bigfoot seem to be replaced by the werewolf. For example, Harry Potter and Twilight, both blockbuster books and movies, have werewolves as major characters. Why do you think that is?
B.R.: We have to remember that monsters are deeply emotional creations. We tend not to react to them in a rational way, so there are many reasons for believing or not believing in them. While evolutionary theory helped do away with the werewolf [right] as a biological reality, it helped create Bigfoot as one. However, Bigfoot is, in some people's eyes, more real. It has a certain amount of scientific support for its existence where the werewolf does not. It's also less threatening.

Q: Well, it is a very intriguing idea. What sort of feedback have you received so far?
B.R.: It has run the gamut, from "That's an interesting idea" to "How can you say Darwin killed the werewolves? I just saw Twilight, and they show werewolves!” So far, no one has called me crazy, though.

Q: How are you going to present your argument?
B.R.: I am using pictures of werewolves, apes, and Bigfoot to trace the visual transformation of the werewolf into Bigfoot. They come mostly from science books and medieval manuscripts. If you look at early drawings of apes, and then cavemen, they look disturbingly like werewolves. I also have an illustration from a Boston almanac from 1785. It’s the first illustration [left] of a primate in North America (based on the work of Edward Tyson), but it is astonishing as to how much it looks like a happy, smiling Sasquatch carrying a walking stick.

Q: If there's someone who believes that the whole Darwin-werewolf-Bigfoot connection has no proof, what would you tell them?
B.R.: I would tell them that as a professional scholar, I looked at the evidence of the written record, saw patterns, made analogies, and came up with a hypothesis that I think is also supported by the visual record. Others might look at the exact same materials I did and come to a different conclusion or find something more interesting in it. That's how the historical method works.

Brian Regal will present his thesis 5 July at the annual meeting of the British Society for the History of Science in Leicester, U.K.

—Preyanka Makadia

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We're halfway through the Origins series of essays in honor of Charles Darwin's 200th birthday, and I'd wager that the other writers who have contributed to it will agree that it's a guaranteed recipe for glorious failure. The origin of life in 2000 words? That's just enough room to give a taste of the wide range of research going on these days but hardly enough to set up a proper banquet. The same goes for my latest essay, on the origin of sex. There, I focused on the intriguing question of why eukaryotes (animals, plants, fungi, and protozoans) have so much sex when it seems to come at a high cost compared with just cloning yourself. But there's an equally intriguing question that I didn't have room to address: Do bacteria have sex, too?

If you define sex as the way we reproduce, then the answer is no. Bacteria (left) aren't born as males and females, and they don't make sperm and eggs. And if you define sex as meiosis—the shuffling of two genomes to produce a new one—-again, the answer is no. But if you define sex as the combining of DNA from two individuals, they've definitely got it.

Viruses can move DNA from one bacterial host to another. Many bacteria carry little extra ringlets of DNA called plasmids that can cause bacteria to join together so that copies of the plasmids can be transferred. Sometimes the plasmids even drag along some of the DNA from the main chromosome. Some species of bacteria will even secrete DNA into their surroundings and slurp up naked DNA they encounter.

This foreign genetic material can be smoothly integrated into a bacterium's own genome. In some cases (known as homologous recombination), the microbe takes up a different version of a gene it already has. It swaps the new version for the old one. In other cases (nonhomologous recombination), it acquires a gene it never had before.

Like eukaryotic sex, bacterial sex has some evolutionary disadvantages. It takes energy to secrete DNA into the environment, for example, and it also takes energy to pump it in and incorporate it into a genome. The energy bacteria put into having sex could be used to grow faster and make more offspring. So, once again, the question arises: Why sex?

In a review in this month's issue of Trends in Microbiology, Michiel Vos of the Netherlands Institute of Ecology takes a look at the potential answers. A lot of them echo the answers that have been offered for the evolution of our own brand of sex. Sex can speed up the evolution of adaptations, for example, by combining beneficial mutations from different bacteria. Sex can bring about entirely new adaptations (such as antibiotic resistance) with the importing of entirely new genes. Sex can add more variation to a population of bacteria, allowing them to adapt to an ever-changing environment, instead of getting stuck in an evolutionary dead end. Sex may help some bacteria do a better job of making us sick by generating new variants that our immune system may not recognize very well.

It's possible, however, that these long-term benefits of sex do not account for their origin through the short-term, generation-by-generation process of evolution. In fact, sex may actually be more of a side effect—what Stephen Jay Gould and Richard Lewontin termed a spandrel. Taking in loose DNA can have an immediate benefit to bacteria that has nothing to do with sex: It's good eating. Some strains of bacteria can live on DNA alone. The fact that sometimes some of the genes they devour end up inserted into their genome does not necessarily mean that the bacteria have evolved a full-blown sexual system. The proteins that swap in new versions of genes during homologous recombination spend most of their time repairing damaged DNA. They may plug new genes in purely by accident.

It's also possible that the adaptation for sex resides not in the bacteria but in their parasites. Plasmids and viruses may evolve increasingly sophisticated ways to move their own DNA from host to host. If they bring genes that benefit their new bacterial host, they benefit as well.

Vos's paper makes the evolution of sex in eukaryotes all the more remarkable. Sex in eukaryotes is a far more complex process, and it's at the core of our biology. Whereas bacteria occasionally swap a gene, eukaryotes blend their genomes every time they reproduce. Biochemist Nick Lane, author of the new book Life Ascending, argues that eukaryotes became different because of a landmark event in their evolution: A microbe took up residence in the eukaryote cell, becoming mitochondria, which we depend on to generate energy. Now the eukaryotic genome was under constant invasion from foreign DNA, coming from close quarters. Worst of all, this foreign DNA included viruslike segments that could make copies of themselves, swamping our own genes. True sex—complete with meiosis—became our best defense. If Lane is right, then it's bacteria we have to thank for not having sex like bacteria.

—Carl Zimmer

Credit: Anlace, English Wikipedia Project

When I sit down to read a scientific paper, I usually brace myself for the worst. I prepare to slog through esoteric, murky language—to have to dig deep to find the buried beauty of science.

But every now and then, you sit down and read a paper that starts like this:

"Picture a pile of freshly cut weeds at the sunny edge of a tropical forest. Metallic green flies dart and circle over it, chasing one another in short dashes. Your eye is caught when a chase ends as one fly grasps another in midair and the pair immediately lands on the pile of weeds. Their genitalia are already coupled, and the male immediately turns to face away from the female. After a few seconds, paradoxically (because he is already securely attached), he begins to court, rhythmically waving his colorful hind legs and tapping the female's abdomen. The courtship continues for a few minutes as the pair remains coupled, and then the flies separate. The female walks down into the pile where she lays eggs (her larvae will feed on the rotting vegetation), while the male rejoins the frenetic chases above the pile."

Why would a male fly wait to court a female until after he has already achieved his evolutionary objective of copulating with her?

The paper is titled Postcopulatory sexual selection: Darwin's omission and its consequences. It was written by William G. Eberhard, an evolutionary biologist at the Smithsonian Tropical Research Institute in Panama, and was just posted online at the Proceedings of the National Academy of Sciences Web site. It offers some wonderfully bizarre examples of the extremes to which evolution reached once sex emerged a couple billion years ago.

Earlier this month, I wrote in Science about the origin of sex. Despite the disadvantages of reproducing with both males and females, sex dominates the animal kingdom and is common among our fellow eukaryotes (plants, fungi, and protozoans). Studies point to several possible benefits that outweigh the cost of sex. Sex may speed up the evolution of adaptations, cleanse our genomes of harmful mutations, or let us fight against parasites more effectively. However sex evolved, it created a new arena in which the evolutionary process could take place. Now reproductive success was not just a matter of surviving and finding enough food. Now it also depended on whether organisms could find a mate.

Darwin recognized this distinctive kind of selection, which he dubbed sexual selection. In his 1871 book, Descent of Man, he argued that males competed with each other for the opportunity to mate with females, and as a result, males had evolved claws, horns, and other weaponry. Darwin also argued that females were attracted to certain males over others, and this preference drove the evolution of gorgeous courtship displays such as the extravagant plumage on some birds.

Over the past 138 years, scientists have discovered a wealth of evidence demonstrating that sexual selection is indeed a powerful force. But it drives evolution in ways that Darwin did not anticipate. In many species, females actually mate with lots of males. And those multiple matings open up yet another arena for evolution. Along with the courtship and battling that goes on before mating, there's an opportunity for lots of strategies for boosting reproductive success after mating.

The underlying logic of postcopulatory sexual selection is simple: Once a male has inserted his sperm in a female, he has not sealed the deal. A female may have the sperm from several males inside of her. There are many strategies that appear to have evolved because they boost a male's reproductive success, from fast-swimming sperm to male genitals that explode after mating, to prevent other males from adding their own sperm.

One of the most intriguing strategies biologists have discovered is when a male courts after the copulation has started. In the case of the flies that Eberhard describes at the start of his paper, it appears that males engage in this after-the-fact courtship so that females will lay eggs immediately after their courtship. If scientists prevent the males from courting during copulation, the female flies fly away without laying any eggs.

Scientists are only starting to test hypotheses about postcopulatory sexual selection, but its effects could turn out to be huge. In fact, it may have bearing on our food supply. Some studies indicate that plants can choose between the pollen of other plants that land on them in order to fertilize their seeds. Plants may even abort fruits that don't come from suitable mates. Such are the unexpected directions in which Darwin's initial ideas have traveled.

—Carl Zimmer

Photo: Stefano Baldacci, Wikimedia

Sex gives nature much of its spice. Fireflies flash through the night to find mates; a flower’s perfume lures insects to carry pollen to distant partners; male bullfrogs croak to impress females. Currently, biologists understand the molecular nuts and bolts of sex fairly well. But the why of sex is still fairly mysterious. Bacteria don’t have to search for mates; they just grow and divide in two. An aspen tree can simply send out shoots that grow into new trees. No muss, no fuss with finding a partner, fertilizing an egg, and joining two genomes.

Darwin felt the whole subject of sex was "hidden in darkness.” In this month's Origins essay, Carl Zimmer sheds light on sex with his examination of progress since Darwin's day in understanding the "why." Today, scientists use genomics and other 21st century tools to search for answers. They are finding hidden signs of sex in the DNA of supposedly asexual organisms and are tracking the evolutionary impact of sex among living populations of animals and plants. Some use sophisticated mathematical models to assess the conditions under which sex can arise. These efforts are providing new hints about how sex first emerged some 2 billion years ago and about the forces that have made it so widespread. The new studies bolster a handful of hypotheses: Sex may speed up evolution, for example, or it may provide a better defense against parasites. In the past, scientists have focused on just one of these hypotheses at a time, but today many argue that several forces may be at work at once.

—Elizabeth Pennisi

Credit: DEA Picture Library/Getty Images

LONG ISLAND, NEW YORK—After an evening that touched on Darwin and the evolution of fish, ants, and humans, the "Evolution: The Molecular Landscape" symposium at Cold Spring Harbor Laboratory was true to its title and headed into the RNA world first thing the next morning. Or rather, the ribonucleoprotein world. Ribonucleoproteins (RNPs) are complexes of RNA and proteins. Many researchers are convinced that the first life depended on RNA and that proteins came later. Those proteins eventually squeezed out RNA from most of its roles carrying out the molecular processes needed for survival. But proteins—or at least simple peptides—were likely in the mix from the very beginning, said Thomas Cech of the University of Colorado, Boulder. He added that "it was never an RNA world." Moreover, it's not just a protein world today. There is increasing appreciation for the amount of RNA transcribed from the genome that doesn't code for proteins. Thus, in partnership with proteins, RNA continues to figure largely in cellular function. A look at RNPs shows that there is a give-and-take between the two partners in the roles they play in the complex.

The discovery of the first ribozymes—RNA enzymes—in 1982 had provided a way out of the chicken-and-egg problem of which came first, proteins or nucleic acids, such as RNA, because today both types of molecules are critical to life. Life started with RNA, then proteins and DNA came along later and outdid RNA as arbiters of biological reactions and information carriers, respectively. Ribozymes evolved into RNPs, which gradually lost their RNA components to produce modern protein enzymes (see diagram). But "we don't see RNA disappearing," Cech said. Instead, it's proved surprisingly versatile.

Cech argues that the same abiotic conditions that favored the formation of nucleic acids likely also favored small peptides. On its own, RNA is so-so as a catalyst, but in RNPs, it continues to play a vital role. The same synergy likely existed in those earliest days, he says.

Take the ribosome. "They are the Trojan horses that came out of the RNA world," said Venki Ramakrishnan of the Medical Research Council Laboratory of Molecular Biology in Cambridge, United Kingdom. Every molecule in the cell is made by the ribosome or by a protein produced by the ribosome. Over the past decade, he and others have worked out that the RNA subunits are at the core, controlling the assembly of amino acids into specific proteins. Its protein partners help hold two RNA subunits in a semirigid structure that shifts back and forth to pull in amino acids and push out the emerging protein chain.

The rigidity of the ribosome is a sharp contrast to telomerase, which was found to be an RNP in 1987. Telomerase typically consists of one RNA and several protein subunits, including a reverse transcriptase protein called TERT that extends the ends of replicated chromosomes to keep them from getting shorter each time they are copied. The RNA specifies the bases that TERT adds. But Cech's group has found that RNA also acts as a flexible scaffold that recruits other proteins, such as a DNA repair protein called Ku. When they alter the RNA so that it doesn't bind Ku, telomerase doesn't work as well. When they add an extra binding site on the RNA for Ku, then chromosomes grow extra-long, he said. The RNA's arms are flexible and swing into different positions. Yet in the lab, Cech's crew has shortened these arms without affecting the RNP's function. "It's a dynamic system where proteins can switch in and out," says Cech.

Both the ribosome and the telomerase show signs that the protein-RNA partnership is dynamic over evolutionary time as well. Cech and his colleagues have discovered that there is a part of the telomerase RNA that helps speed telomerase activity. "He's finding new functionality in the RNA," says Susan Lindquist of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts. "A new region has come in and contributes to catalysis."

In the ribosome's case, proteins are lending the helping hand. Ramakrishnan reported the discovery of an arm of one of the ribosomal proteins that extends deep into the RNA where transfer RNAs bind and deliver amino acids. Now instead of depending on RNA alone, "protein tentacles are assisting the process," says Ramakrishnan. In mitochondrial ribosomes, proteins have taken on an ever-larger role. The ratio of RNA to protein in the cell's ribosomes is 2 to 1; but in mitochondrial ribosomes, the ratio is roughly 1 to 2. This ribosome looks about the same, but most RNAs have been replaced by protein, leaving just a small RNA core.

These examples show that RNPs "are not decaying," says Lindquist. "They are continuing to evolve."

—Elizabeth Pennisi

Illustration credit: Harold White, University of Delaware

Work being reported today in Biology Letters about pitcher plants would please Charles Darwin. This curious naturalist was so intrigued by carnivorous plants that he wrote a 400-page book, Insectivorous plants, detailing his thoughts and observations on these unusual species. He was fascinated by the similarities in the insect traps of unrelated plants and demonstrated that these plants had the ability to digest and absorb the prey they caught. This week, researchers report on how one species, a pitcher plant found in Canada and the eastern United States (left), snags its dinner. At issue was whether a red color or a sweet treat is what makes this death trap so appealing.

In 2007, H. Martin Schaefer of the University of Freiburg in Germany evaluated the role of pitcher color in luring insects. Using 20 pitcher plants (Nepenthes ventricosa) from Southeast Asia, his team painted half the pitchers green and half of them red, then placed the plants outside, counting the number of trapped insects after 1 and 2 weeks. They found that red plants caught more prey, particularly flies. They assumed that the plants smelled alike—like paint—to the insects. Others had suggested that the UV marks or visual stripes on pitchers were needed to reel insects in, but the opaque red pitchers were quite effective without such decorations, they reported.

But Aaron Ellison of Harvard University wasn’t satisfied with this finding, given that the plants were not in their native environment, where typically they trap ants and termites, not flies. He wondered whether pitcher plants were taking advantage of a sweet tooth in their victims. Pitchers produce excessive amounts of nectar, separate from what the flowers make. And earlier this year, Ganesh P. Bhattarai and John D. Horner of Texas Christian University in Fort Worth had suggested that odors, including sweet ones, could be important attractants.

Ellison recruited Katherine Bennett, a local elementary school teacher who had become interested in science through a Harvard program for schoolchildren to help scientists gather data. Bennett suctioned prey carcasses from pitchers of 25 Sarracenia purpurea pitcher plants growing in a Massachusetts bog, then checked again 3 days later for new prey. After several rounds of suctioning and inventorying the plants, she and Ellison collected the plants and assessed their redness by measuring spectral reflectance. Next, they made 70 plastic centrifuge tubes into “pseudopitchers” painted either green, red, or green with red stripes. Ten were left unpainted. They streaked half the pitchers with thickened corn syrup and embedded all the tubes at angles in a bog close to the plants surveyed earlier. Several times, they counted the trapped insects, comparing the pseudopitchers’ body count with the real plants’.

They retrieved about 350 prey each from real and nectar-streaked fake pitchers, whereas the unsweetened pseudopitchers garnered only about 60, they report in Biology Letters. Ants were the most susceptible to the nectar lure. The amount of red didn’t seem to matter much at all. “We only manipulated the color of pitcher plants," comments Schaefer. "This study goes one step further and [shows that] the effects of sugar rewards outweigh those of color. This experimental support has been lacking.”

As for Bennett, she says, her experience has “transformed the way I teach science.”

—Elizabeth Pennisi

Photo: Katherine Bennett

With swine flu circulating the globe, it’s appropriate that May’s Origins essay is “On the Origin of the Immune System.” Immunology is the study of how we and other animals defend ourselves against pathogenic microorganisms—bacteria, viruses, and parasites, for example—and this battle goes back to the beginning of evolution. The first multicellular creatures must have had to learn how to be nice to their own cells yet attack any invading cell trying to exploit their resources. Indeed, when biologists look at sponges and other “simple” creatures at the base of the evolutionary tree, they see many of the same microbial defenses that we and other complex animals use, which suggests that at least some form of immunity arose very quickly in the evolution of animals. But those ancient defenses only constitute what scientists call the innate immune response, an all-out molecular and cellular assault on infected tissue. Most vertebrates have a second level of defense, the adaptive immune response, that targets, and remembers, specific microbes. It’s this adaptive immune response, dependent on white blood cells called B and T cells, that physicians elicit when they vaccinate a person against a virus, for example. In a scientific detective story that has played out over the past few decades, researchers have shown how this adaptive immune response arose after innate immunity, and they have teased out the details of the fortuitous event, a random DNA insertion in an opportune spot, that was the key to its birth. The research on this “big bang of immunology” even played a key role in a 2005 trial pitting scientists and educators against those doubting evolution and seeking to diminish its teaching in school systems in the United States.

—John Travis

Illustration: Katharine Sutliff/Science

Some 300,000 species strong, flowering plants dominate terrestrial landscapes, prompting awe and wonder dating from the days of Charles Darwin about how this group arose. (See this month's Origins essay.) And although the blossoms themselves contributed much to the success of angiosperms—attracting and making efficient use of insects and other pollinators—they are not the only feature that gave angiosperms a leg up on earlier seed plants. The way angiosperms provide nutrients for their seeds represents an underappreciated, cost-saving innovation that arguably made human civilization possible. It’s called the endosperm, and it's what pops in popcorn (left) and forms the bulk of what's in flour, rice, oats, and other grains, providing humans with two out of every three calories worldwide. “You take endosperm off the table, and you have fern fiddleheads and not much more [to eat],” says William "Ned" Friedman, a botanist at the University of Colorado, Boulder. “Even a grain-fed cow is really processed endosperm.”

Endosperm is the nutrient-filled tissue that sustains the growth of the embryo within a seed, sometimes early in development and sometimes later, once the seed has germinated. It arises through an innovation called “double fertilization.”  Each pollen grain produces two sperm, one of which fertilizes the “egg” and one of which merges with a so-called central cell that’s colocated with the “egg” in the female embryo sac. That latter fertilization sets off the growth and development of endosperm, which becomes packed with starches, proteins, lipids, or oil, depending on the species. Endosperm can be solid, as in wheat, or liquid, as in coconut milk. This double fertilization ensures that the embryo will have the sustenance it needs to complete its development.

Pines, firs, ginkgoes, and other gymnosperms also have nutritive tissue, but their tissue is prepared well in advance, laid down as the egg is maturing and well before fertilization. “It’s a slow process,” says Friedman, and should subsequent fertilization fail, this effort goes to waste. By jump-starting embryo and endosperm development simultaneously, angiosperms save time and cut down on wasted effort. “My sense is this [change] opened up all kinds of opportunities,” he adds. For example, now life cycles could be completed in a season, making possible annuals and other rapidly reproducing plants. But how did this just-in-time provisioning evolve?

Photo Credits:  William "Ned" Friedman.

No bigger than specks of dust, cryptospores are one of our largest windows into the deep history of plants. These ancient spores and pollen show up in the fossil record between 465 million and 407 million years ago, a key moment for Earth’s greenery. During the first half of that period, the nonvascular land plants—mosses, liverworts, and hornworts—held sway, dominating the landscape for 30 million years. But eventually, vascular plants—ferns and seed-bearing plants—evolved and gradually took over. By examining the shapes and structures of cryptospores collected during oil explorations, paleobotanists have been trying to pin down this transition. New finds now push back the date when vascular plants appeared by almost 30 million years, to about 450 million years ago, Philippe Steemans of the University of Liège, Belgium, and colleagues report in the 17 April issue of Science.

Cryptospores differ from modern spores and pollen in that they come in clumps of two or four, having failed to separate as modern pollen does into individual cells. Thus these dyads and tetrads (above; scale is 10 micrometers) are diagnostic for ancestral land plants. Spores that have disassociated from these clumps represent more modern plants, and folds and bumps on spore surfaces distinguish species and thus are indicative of diversity.

Since 1990, Steemans and Charles Wellman of the University of Sheffield in the United Kingdom have been retrieving fossils from boreholes dug for oil exploration in Saudi Arabia. They dissolve the rock in different solvents to remove carbonate and silicate materials and examine the remaining organic material under light and scanning electron microscopes. They typically find marine fossils, which help them determine the age of the rock, as well as spores and pollen.

In the most recent samples, the cryptospores at first seemed quite ordinary. But when they looked closely, Steemans and Wellman found single spores—called  trilete spores (left; scale is 10 micrometers)—dispersed among the dyads and tetrads. “Our first reaction was to think that the samples had been contaminated by younger material,” Steemans recalls. But an independent analysis in a second laboratory turned up the same ancient trilete spores.

“These generally don’t appear until much later,” about 436 million years ago, says Wellman. Thus these newly described, 450-million-year-old cryptospores “probably represent the origin of vascular plants.”

—Elizabeth Pennisi

Photo Credit: P. Steemans

As I pointed out in my essay on the origin of flowering plants, a key breakthrough came in the late 1990s when molecular studies showed water lilies and the New Caledonia plant Amborella to be toward the bottom of the angiosperm tree. With these basal lineages in place, botanists could begin to tease out the more primitive angiosperm traits. More recently, another plant, this one masquerading as a monocot, a major group of flowering plants that includes grasses, orchids, and palms, has been reassigned to the primitive part of the tree, near the water lilies. Found in Australia and New Zealand, with one species in India, these tiny plants, which make up the Hydatellaceae family, like to be submerged, sometimes more than a meter deep, sending up flower stems 1 to 3.5 centimeters high with flowers 1 or 2 millimeters in size. From afar, they can look like a lawn of underwater moss.

Though very odd in appearance and lifestyle, the Hydatellaceae had seemed to fit best with grasses: Both have reduced flowers, for example, and their seeds seemed similar in having what looks like one seedling leaf and not two as in the majority of angiosperms. At least one gene study has placed one of this group, Trithuria submersa (left), squarely among the grasses—although later this turned out to be a contaminant sequence.

Fascinated by this oddball, Sean Graham of the University of British Columbia Botanical Garden and his colleagues did a more thorough gene analysis. They isolated chloroplast genes from Trithuria and compared them to the same genes in a variety of other species. To their surprise, Trithuria proved to be quite a distant relative to grasses. Instead, this plant branched off the angiosperm family tree at about the same place as water lilies. This arrangement held fast even after Graham and his colleagues analyzed the data several different ways. Analyzing sequences from a nuclear gene and chloroplast genes from another Hydatellaceae, Hydatella inconspicua, supported this new classification as well, which they reported on in 2007.

From this new perspective, botanists have begun to realize that Hydatella and Trithuria really do fit nicely down at the base of the angiosperm tree, not high up among the later-evolving monocots. Their seeds have a cap called an operculum just like water lilies. Their embryo sacs, specialized sexual tissue of seeds, have fewer cells compared to those of more later-evolving species. And their carpels, protective sheaths surrounding the seeds, start out as cup-shaped, with margins that do not completely fuse as in carpels of most other plants. These traits in Hydatella “fit with an emerging picture in which the earliest angiosperms likely had many of these features,” says Graham. It also raises the question about whether the first flowering plants were aquatic, but many botanists don't think that was the case.

Now firmly ensconced among the water lilies, the Hydatellaceae are attracting quite a bit of interest. “We are trying to develop Hydatellaceae as a model organism for early-divergent angiosperms and are successfully growing and flowering it at Kew, though so far we have not managed to set seed,” says Paula Rudall, a botanist at the Royal Botanic Gardens, Kew. Her team has even isolated many of its genes.

Rudall, Dimitry Sokoloff of Moscow State University in Russia, and their colleagues have been going over these species micrometer by micrometer as well as second by second, probing both the structure and the development for clues about the most ancient angiosperms. The Trithuria flower seems to be inside-out, with stamens at the center instead of rimming centrally located carpels, they reported earlier this year, illustrating their paper with stunning pictures of the flower’s development.

Graham is refining the relationships among these and other basal angiosperms. Others, including his student Will Iles, are taking a close look at the species within this group. Already, these botanists have concluded that there’s just one genus, not two as had been thought, and at least 12 species, not 10. "We found that previously, males and females of the same species (some species are sexually dimorphic) had been included in different genera,” notes Rudall.

Graham hopes that one day botanical gardens will exhibit Hydatellaceae. “It’s not going to be a spectacular [display],” he admits, but for the study of angiosperm evolution, these plants’ contribution could be enormous.

—Elizabeth Pennisi

Credit: Dennis Wm. Stevenson, New York Botanical Garden

Tracing the origin of flowering plants has long been a challenge for evolutionary researchers, as discussed in this month's Origins essay. Paleobotanist David Dilcher thinks part of the reason is that researchers in his field misidentified fossil plants as members of modern groups. Back in 1979, he and a colleague reanalyzed fossil leaves collected from 45-million-year-old clay pits in Tennessee. Careful cleaning revealed previously unnoticed stipules, small outgrowths from the base of the leaves, calling into question the fossils’ supposed identity as modern corkwood. A close examination of the venation pattern and the cuticle of the leaves convinced Dilcher that these leaves were an extinct group belonging to the coffee family. Dilcher, now at the Florida Museum of Natural History in Gainesville, talks about the impact of this and subsequent work by others on understanding flowering plants.

Often the phrase “the origin of the flowering plants is an abominable mystery” can be read in popular and scientific literature. This phrase is credited to Darwin and comes from a letter that Darwin wrote to J. D. Hooker on 22 July 1879 (Darwin, 1905). It represents Darwin’s frustration with the paleobotanical record of his time. The literature available to Darwin in the 1870s shows that when flowering plants are first found in the fossil record, they are nearly all given names of extant genera. At the time of Darwin, there was no evolution that could be demonstrated from the fossil record of flowering plants. This record was based almost entirely upon impressions and compressions of fossil leaves, and paleobotanists of the 19th and first half of the 20th centuries looked for “matches” or similar leaf types with the leaves of living flowering plant genera. This ”leaf matching” can be done if one does not look closely at detailed characters of fossil and living leaves. When characters such as fine venation, epidermal cell patterns, trichome types, and stomatal complexes are examined carefully (Dilcher, 1974), a different view of early flowering plants emerges.

 

Such was the case for Paleorubiaceophyllum eocenicum (far left), which was once classified as Leitneria floridana (near left) but which really represents an extinct group of plants.

Darwin’s “abominable mystery of the origin of the angiosperms” can be understood when careful observations of characters are made. With the study of detailed leaf venation and leaf epidermal cell characters, it is clear that many of the earliest flowering plants represent extinct species, extinct genera, extinct families, and perhaps even extinct orders (Dilcher 1974, 2000). This paradigm change has caused a revolution in the study of fossil flowering plants which only in the past 40 years has begun to present a realistic record of extinct flowering plants.

It seems to be human nature that when a fossil leaf is found, the first question asked is what is its living counterpart. When fossil leaves are examined only as hand specimens, using gross form, it is easy to find leaves of trees living today that “match” the fossils. The success of early paleobotanists depended upon making such matches. It has taken a philosophical shift in angiosperm paleobotany in order for researchers today to strive to understand relationships between fossil and living plants, based upon detailed characters, rather than feeling the need to find a living genus to which they can name a fossil. Using character analyses, we now have an emerging new fossil record of flowering plants with many extinct taxa that would have delighted Darwin. This new record is one he could have understood because it demonstrates the evolution of flowering plants, a major group of organisms on Earth. We do not yet know all the details, but there is no longer any “abominable mystery” to the origin of flowering plants.

—David Dilcher

Darwin, F. (Ed.). More letters of Charles Darwin. Vol. 2. (Murray, London, 1905).

Dilcher, D. Approaches to the identification of Angiosperm leaf remains. The Botanical Review, 40:1, 1 (1974).

Dilcher, D.  "Toward a new synthesis: Major evolutionary trends in the Angiosperm fossil record. pages." Variation and Evolution in Plants and Microorganisms: toward a new synthesis 50 years after Stebbins. F. J. Ayala, W. M. Fitch, and M. T. Clegg, Eds. (National Academy Press, Washington, D.C., 2000), pp 255-270.

Credits: Paleorubiaceophyllum eocenicum: H. Wang and D. L. Dilcher; Leitneria floridana: J. S. Peterson, USDA NRCS NPDC. Missouri Botanical Garden.

Last week, I had a rare opportunity to exchange ideas about the origins of art and symbolism with scientists, students, and the general public in India. After reading my 6 February essay, the president of the Indian Academy of Sciences, Dorairajan Balasubramanian of the L. V. Prasad Eye Institute in Hyderabad, invited me on a lecture tour as part of the academy’s 75th anniversary. For a busy 8 days, I gave lectures and met informally with small groups of students in both the “hard” sciences and the humanities at Jawaharlal Nehru University in New Delhi, the Centre for Cell and Molecular Biology in Hyderabad, and the Indian Institute of Technology Madras in Chennai (the city formerly known as Madras), among other places.

My talk, which I called “What Made Humans Modern?” after the title of an earlier story I had written for Science, focused on how archaeologists and anthropologists have tried to trace the origins of art and symbolism by using proxy indicators of the cognitive mechanisms involved, such as the ritual use of ochre and sophisticated toolmaking. I also described possible Darwinian explanations for the evolution of advanced cognition in modern humans.

I was very impressed with how serious and engaged my listeners were. One question that came up after nearly every lecture was why our species became so far advanced cognitively over all other animals. In response, I suggested (rightly or wrongly) that the human line, which split from the chimp line around 5 million to 7 million years ago, might have had a “lucky break” when it went bipedal while other animals did not, as that evolutionary development later allowed brain expansion and other adaptations such as greater flexibility of the hands.

Some audience members were skeptical that symbolic behavior, especially language, was unique to modern humans, citing the dances of honey bees, bird songs, and dolphin sounds, among other indications of sophisticated animal behavior. I suggested that although we should not minimize the talents of other animals, most of their impressive abilities are nevertheless stereotypical and instinctive. They bear little resemblance to the kind of nearly endless innovation and nuanced expression represented by human language, art, and music. (See my article about the apparent “gap” between animal and human cognition.)

But as I fielded such questions, and in the talk itself, I was careful to present the various scientific viewpoints about these often controversial questions and avoid coming down hard in favor of any particular conclusion. My audiences seemed particularly responsive to that more journalistic approach, which allowed them to make up their own minds about the mysteries of human origins.

—Michael Balter

Photo Credit: Vivek Handa

Although angiosperms outnumber other land plants nine to one, there’s still a vast “green” world beyond those blossoming trees, herbs, shrubs, and grasses. Indeed, land plants are but a twig on the tree of green eukaryotic life (below), one that extends from a major branch called the streptophytes.

The other branch, Chlorophyta, includes many of the green algae. Sprouting off toward the bottom of the chlorophyte branch are tiny organisms called Micromonas, thought to most closely represent this tree’s earliest ancestor. Two of their genomes are newly described in today's issue of Science.

No bigger than a bacterium, these minuscule marine eukaryotes have surprisingly sophisticated genomes, says Alexandra Worden, a marine microbial ecologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California. Her team has deciphered the genomes of two strains of Micromonas (lower left), which proved different enough to qualify as independent species. She chose these organisms because they thrive from the tropics to the poles and likely play an important role in the ocean’s food chain and carbon cycle. They are so small that they are hard to characterize and understand without the genes in hand, and she’s very eager to learn how they will respond to a changing environment and how they fit into the marine food chain. (See video.)

Overall, the Micromonas genome is about 21 million bases long, with 10,000 genes, 2000 more than its much more streamlined relative, Ostreococcus, which has already been sequenced, twice. About 20% of the genes found in Micromonas but not in Ostreococcus are genes generally thought to have evolved only in land plants, not earlier, her team reports. For example, the team finds that Micromonas has a gene called YABBY, which is missing from other green algae and even moss, and is thought to be related to the development of leafy plants. Given that leaves don’t exist in these algae, she thinks YABBY must have played another role early in green eukaryotic evolution.

One challenge is that many genes unique to Micromonas “are genes we don’t know the function of,” she points out. “That’s disappointing. If we can figure out their functions, that’s really going to give us new insights into what these organisms have to deal with [in their environments] that we are not thinking about.”

—Elizabeth Pennisi

Diagram: Adapted by P. Huey/Science

Image: A. Z. Worden, T. Deerinck, M. Terada, J. Obiyashi, and M. Ellisman (MBARI and NCMIR).

What happens when you mix rock music with evolution?

You get Darwin Rocks!, a team of eager ecologists who have made a music video and a computer game to get people interested in Charles Darwin’s seminal theory. The scientists, from the University of Tübingen in Germany, have put together a music clip called “Struggle for Love” featuring a rock soundtrack designed to grab the attention of 15- to 25-year-olds. “We were aiming for a simple message,” says team leader Nico Michiels. “Most people misunderstand what evolution is all about: In the end all that counts is reproduction.”

The video opens with a Darwin look-alike scientist staring intently into a petri dish. The dish contains a strange sci-fi world where the “survival of the fittest” is battled out by microscopic people on a tiny soccer pitch. Several generations later, it’s not the team with the strongest and most ambitious players that wins but the team with the most players—that is, the one that reproduces most. “That’s why the song is written around love and reproduction, instead of focusing on strength,” says Michiels. “Also, we used [sports] to attract the attention of people who would never normally look at a clip like this.”

The video was made in collaboration with students from music schools in Heidelberg and Mannheim and a film school in Munich and thus received a lot of input from the age group it is targeting, says Michiels.

The team also designed a computer game based on the idea that it’s not just animals and plants that evolve—so can music. The game starts with a "musical primordial soup" where the user selects tunes he or she likes from a list. Based on that subset, the program creates "offspring" tunes, which the user also rates. This process of listening and rating hones the evolution of the music. “The user is basically the selective environment. They stand for natural selection,” explains Michiels.

Michiels says the music video and game are nonprovocative ways of demonstrating evolution: “I’d rather generate curiosity about evolution instead of being critical about other people’s beliefs,” he says. “If you provoke moderately religious people, you might lose them. But if we just talk about evolution, you might just win them.”

The video and game were made after the team won a German “creativity contest,” in which evolutionary scientists had to come up with innovative ways of presenting Darwin’s theory. Both Michiels's team and the contest were funded by the Volkswagen Foundation.

—Claire Thomas

What would our world be like without flowering plants? Some 300,000 species of angiosperms are alive today. Their blooms color and scent our world; their fruits, roots, and seeds feed us; and their biomass provides clothing, building materials, and fuel. And yet this rapid spread and dominance of the terrestrial landscape, which took place perhaps 100 million years go, apparently happened in a blink of geological time, just a few tens of millions of years.

The father of evolution couldn’t quite fathom it. In 1879, Charles Darwin penned a letter to British botanist Joseph Dalton Hooker, lamenting an “abominable mystery” that threw a wrench into his theory of evolution: How did flowering plants diversify and spread so rapidly across the globe? Now, 130 years later, botanists are finally beginning to make sense of what has made this plant group so successful and are sorting out how, and when, flowers got started—and from which ancestor. April's Origins essay, "On the Origin of Flowering Plants," discusses how researchers now have analytical tools, fossils, genomic data, and insights that Darwin could never have imagined, all of which make these mysteries less abominable. Over the past 40 years, techniques for assessing the relationships of organisms have greatly improved, and gene sequences as well as morphology now help researchers sort out which angiosperms arose early and which arose late. New fossil finds and new ways to study them—with synchrotron radiation, for example—provide a better sense of the detailed anatomy of ancient plants. And researchers from various fields are figuring out genomic changes that might explain the amazing success of this rapidly evolving group. Questions still remain, particularly about the nature and identity of the angiosperm ancestor itself. But modern botanists are hopeful that the abominable mystery is well on its way to being solved.

—Elizabeth Pennisi

Credit: Reproduced with the kind permission of the Director and the Board of Trustees, Royal Botanic Gardens, Kew

Cambridge University, Darwin Online, and the Huntington Library are trying to track down as many first editions of Darwin's On the Origin of Species as possible before the anniversary of its publication in November. They are looking for books in private collections as well as in institutions. Already, they have come across Francis Darwin's copy, with his annotations, in a private collection.

Here is more information about the census.

If your chrysanthemums look stunted and ugly, take comfort. They're infected with a parasite that may tell us a lot about how life began.

Chrysanthemums and some other plants are victims of invisible enemies with the wonderfully sci-fi name of viroids. Scientists discovered viroids in the 1960s while they were trying to figure out why potatoes sometimes grew in weird long shapes (left). They suspected that this so-called potato spindle tuber disease was caused by an infection, because the condition seemed to be spread slowly through potato fields. As for the infectious agent, it seemed likely to be a virus. After all, viruses have long been known to be able to change the shapes of plants they infect. Looking for a virus in the slow-growing potatoes would have slowed down the search immensely. But researchers figured out how to transfer the disease to fast-growing tomatoes, which became stunted after being infected.

Yet even with this advance, the scientists still struggled to figure out what was making the plants sick. They used centrifuges to get rid of particles larger than certain sizes and found that whatever was infecting the plants was amazingly small—far smaller, in fact, than any known virus. And its chemistry was different from that of any known virus. Viruses carry their genetic information in molecules of either DNA or RNA (a single-stranded counterpart to DNA). They also keep this genetic information in a protein shell. The scientists ground up infected tomato leaves and mixed them with enzymes that chop up RNA. They could no longer use that mixture to infect other plants—suggesting that the pathogens used RNA for their genetic material. And indeed, when the scientists repeated the experiment with enzymes for cutting up DNA, the material was still infectious. But then a third experiment yielded a weird result: When the scientists used enzymes to cut up proteins, the material could still make plants sick. In other words, the pathogen seemed to be nothing but a tiny snippet of naked RNA.

It took years of tests to finally confirm that the potatoes were getting sick from bits of raw RNA. Scientists dubbed them viroids (meaning "like a virus") and went on to discover them in a number of plants, including chrysanthemums. In fact, it turned out that a disease that had nearly wiped out the American mum industry in the mid-1950s had been caused by a viroid of their own. (For some reason, no one has found an animal viroid.)

A viroid can contain as few as 250 nucleotides. That's extraordinarily small: The human genome is 3.3 billion nucleotides long, and a single protein-coding gene may be several thousand nucleotides long. Yet that's enough genetic information to let a viroid infect a plant and replicate itself by taking advantage of the enzymes the plant uses to replicate its DNA. Normally, the enzymes pull apart DNA's two strands and add nucleotides to make two new strands, using the old strands as templates. But viroids trick these enzymes into copying their single-stranded RNA. The enzymes use the viroid as a template to make a new viroid progeny. Plants have evolved defenses against these viroids that prevent them from being duplicated. But viroids can often escape the attacks of their hosts, leaving the cell to infect another.

While plant scientists try to figure out how to cure crops of viroids, other biologists are fascinated by them because they strip the processes of life down so far to the bone. Recently, Rafael Sanjuán of the University of Valencia in Spain and his colleagues decided to see how much viroids mutate. Humans, chrysanthemums, and other multicellular organisms have many ways of lowering their mutation rate. They can proofread their DNA as it is copied and correct errors. Bacteria are not quite so careful, but they can still repair a lot of DNA damage. Many viruses are decidedly sloppier. What's intriguing about this pattern is the size of the genomes involved: The higher the mutation rate, the smaller the genome.

Viroids offered a fresh opportunity to test this relationship, because they are hundreds of times smaller than viruses, the smallest genomes for which mutation rates had been estimated. Sanjuán and his colleagues infected chrysanthemums with viroids and then let them breed. The researchers then harvested the new viroids and scanned their genomes for mutations. In particular, they looked for mutations that would keep the viroids from replicating, because these must have been new. (They couldn't be carried down from earlier generations, because they keep the viroids from replicating.) To make sure these really were lethal mutations, the scientists engineered viroids with these mutations and injected the mutant viroids into plants. The plants didn't get sick.

Sanjuán and his colleagues found many mutations. The viroids are the fastest mutators ever found, mutating thousands of times faster than the previous record holders, they report in the 6 March issue of Science. And, as this chart* shows, viroids fall right where you'd expect along the genome size/mutation rate continuum. (The mutation rate is measured in the chances any nucleotide has of mutating per generation.)

As I wrote in my Origins essay in January, many scientists are now persuaded that the earliest form of life on Earth was based not on DNA, RNA, and proteins, but on RNA alone. Some are now building RNA-based protocells to see if they can grow, replicate, and evolve. If life did start out in this RNA world, the early protocells would have had only a few relatively short RNA molecules. As Sanjuán and his colleagues observe, viroids bear a striking resemblance to them. According to the RNA world hypothesis, the original RNA molecules of life would have had to have carried out two different kinds of functions. They'd have to store genetic information and also speed up chemical reactions the way enzymes do today. The viroids that Sanjuán and his colleagues studied contain a stretch of RNA called a hammerhead enzyme that speeds up the viroid's duplication in an enzymelike way.

If early RNA-based life forms had genomes on par with those of viroids, they would have had a gigantic mutation rate. We could not survive with such a high mutation rate because we have such a big genome, with so many vulnerable spots where mutations could deal lethal blows. With a much smaller genome, viruses can survive at a higher mutation rate. And viroids, smaller still, afford mutations an even smaller target.

But the reverse is also true: Without a way to lower their mutation rate, viroids are trapped below a so-called error threshold. The evolution of very accurate gene replication was thus probably a crucial stage in the emergence of more complex life. If life had stayed sloppy, we'd all still be little more than viroids.

— Carl Zimmer

*Source: S. Gago et al., "Extremely High Mutation Rate of a Hammerhead Viroid," Science, 6 March 2009 doi: 10.1126/science.1169202

Try to picture the world without photosynthesis. Obviously, you’d have to strip away the greenery. Not just the redwoods and sunflowers, but the humble algae and the light-capturing bacteria that nourish many of the world’s ecosystems. Gone, too, would be everything that depends on photosynthetic organisms, directly or indirectly, for sustenance—from leaf-munching beetles to meat-eating lions. Even corals, which play host to algal partners, would lose their main food source.

Given its importance in making and keeping Earth lush, photosynthesis ranks high on the top-10 list of evolutionary milestones. In Science's Origins essay this week, author Mitch Leslie describes how scientists are delving into ancient rocks and poring over DNA sequences to try to piece together how and when organisms first began to harness light’s energy.

Although most modern photosynthesizers make oxygen from water, the earliest solar-powered bacteria relied on different ingredients, perhaps hydrogen sulfide. Over time, the photosynthetic machinery became more sophisticated, eventually leading to the green, well-oxygenated world that surrounds us today. In the lab, some biochemists are recapitulating the chemical steps that led to this increased complexity. Other researchers are locked in debates over just when this transition happened, 2.4 billion years ago or much earlier. 

A chilling tale of science, romance, politics, and death in the Soviet Union set the stage for the National Evolutionary Synthesis Center’s (NESCent's) third annual Darwin Day Symposium, held on 21 February at the Sigma Xi Center in Durham, North Carolina. The birthday boy himself was rarely mentioned; rather, the event emphasized modern applied evolution. Theodosius Dobzhansky famously wrote in 1973, "Nothing in biology makes sense except in light of evolution." But, as speaker Fred Gould pointed out, evolution has become far more than a way to make sense of things. “Today, your quality of life depends on application of a rigorous understanding of evolution,” he argued. And thus began a series of talks that addressed evolutionary approaches to practical challenges in agriculture, disease, and conservation.

But first, Gould provided the opening historical overview—a convoluted story centered on Soviet geneticist Nikolai Vavilov (1887-1943) and his nemesis, state-supported pseudoscientist Trofim Lysenko (1898-1976). Vavilov is best known for his studies of global crop evolution and diversity, as well as his efforts to breed better cereal crops based on Mendelian genetics. Lysenko, on the other hand, is remembered as a proponent of crackpot notions about the inheritance of acquired traits. Despite his more valid scientific approach, Vavilov fell out of favor with socialist leaders and died of starvation in prison, after criticizing Lysenko’s unfounded claims. Gould’s account (like this recent article in The New York Times) was a clear reminder that the practice of science has been, and still is, shaped by its political and ideological milieu.

“You trashed our heroes,” lamented one audience member after hearing how the evolutionary giants Ronald Fisher, Francis Galton, and J.B.S. Haldane supported eugenics or Lysenkoism. But Gould and the other speakers were ready to add their own stories of how politics and ideology affect the way they fund or present their work. Gould, for instance, believes that genetically engineered insects can be used to manage medically and economically important insect pests. But he worries that this approach will meet with resistance because of current attitudes toward genetically modified crops and the big businesses that market them.

Barbara Schaal encountered a different kind of roadblock in her work on the evolutionary genetics of cassava. Although it is a dietary staple in much of the developing world, cassava lacks many important nutrients. Millions would benefit from an improved cassava—but because it is not a cash crop and is not grown in the United States, Schaal found it difficult to fund her initial research. Eventually, her team produced molecular phylogenies of cassava and its wild relatives to pinpoint the crop’s likely origin in the Brazilian Amazon. There, they discovered that villagers were growing varieties with vitamins, pigments, and sugars unknown in the common domestic cassava. Some of those varieties are now involved in a project, funded by the Gates Foundation, to produce a nutritionally complete cassava for widespread cultivation.

Daniel Faith came all the way from Sydney, Australia, to discuss how evolutionary biology can help prioritize conservation areas. His research is part of a growing body of work that highlights the importance of plant phylogenetic diversity, rather than total species diversity, in preserving the characteristics of an ecosystem. Regions with the greatest phylogenetic diversity include more distantly related species and represent evolutionary history more completely—even if they include fewer total species. Faith argues that phylogenetic diversity should, therefore, inform conservation decisions, but he also talked about the challenge of communicating and applying the results without embracing a “naïve efficiency” that sanctions extinction as long as phylogenetic diversity is preserved.

Katia Koelle left the macroscopic world of plants and entered the invisible realm of viruses. She described how an improved understanding of rapid viral evolution can inform efforts in disease control. And in an excursion from the applied theme of the day, Steven Benner talked about how he and his colleagues use evolutionary trees to infer the sequences of ancestral proteins. By recreating those ancestral proteins and studying their function, Benner tries to make evolutionary “just so” stories more concrete.

Although free and open to the public, the symposium drew a largely academic crowd of biology students, faculty members, and postdocs. About 80 people sacrificed at least part of a sunny Saturday to sit in a dim auditorium and take in the talks.

NESCent plans to post video of the symposium online—watch the symposium site for updates.

—Elsa Youngsteadt

Our lives depend on a microscopic tangle of molecules called the ribosome. The job of the ribosome is to use the sequence of DNA in a gene to build a corresponding protein. Other enzymes first build a single-stranded copy of the gene from RNA, and then a ribosome grabs onto the RNA and "reads" it, using the information to decide which building block to grab next in order to build a protein. (Here's a video of the process.)

The ribosome has two parts that come together around the RNA like a pair of jaws, and each one is a fiendish nest of complexity. Each of the jaws, known as subunits, is a mix of protein and RNA. This animation, created by David S. Goodsell, shows the structure of the large subunit in bacteria. It contains two RNA molecules in it, a big one here colored orange, and a small one colored yellow. The proteins wrapped around them are in blue. The big RNA molecule alone is a marvelous migraine of complexity. It measures 2900 nucleotides long, and it twists and folds in on itself again and again to form the supreme Gordian knot.

All living things make ribosomes and use them for the same essential purpose. It is a sign of our common heritage with baobabs and starfish, with plague and mold. But the fact that the ribosome is everywhere makes its evolution difficult to study. There is no partial ribosome in nature to offer clues to how it emerged. But in this article in the 19 February issue of Nature, Konstantin Bokov and Sergey Steinberg, two biochemists from the University of Montreal, offer some new hope: It's possible that the evolution of the ribosome is recorded in its very own tangles.

Bokov and Steinberg show that the ribosome is like an onion, with outer layers that can be peeled away from inner ones. The proteins of the ribosome help keep it stable, but they themselves do not actually weld together new proteins. That's the work of the ribosomal RNA. As I wrote in my January Origins essay, many researchers now argue that DNA and proteins were not the first biological molecules to emerge; before they existed, life was based on RNA alone. The origin of the ribosome, Bokov and Steinberg argue, is really the origin of the ribosomal RNA.

Ribosomal RNA is made up of dozens of loops, and loops upon loops, all folded in on each other. But Bokov and Steinberg point out that they have an onionlike order of their own. They inspected all the loops, looking for ones that could be removed without altering the rest of the RNA molecule. They found 19 of these expendable loops. Next, they looked at the loops that had kept those 19 loops stable but which could be eliminated without affecting the rest of the RNA. They found 11 such loops. Below these two layers, Bokov and Steinberg found yet another layer of loops, and another, and another, until they had reduced the ribosomal RNA to a tiny fragment, a core on which all the rest depended.

Bokov and Steinberg propose that the seeming complexity of the ribosome is something of a mirage. Its evolution was actually pretty simple. It evolved from a tiny piece of RNA, perhaps only 110 nucleotides long. At first, this molecule didn't build proteins; it may have carried out some kind of reaction on other RNA molecules in RNA-based cells. Then mutations accidentally duplicated the fragment, building new units that could fold back on the older units. This protoribosome may have been able to add random building blocks together. New layers of loops evolved, making the ribosome more precise, able to build specific proteins when it read specific pieces of RNA. Newer loops made the ribosome even more stable and thus able to crank out proteins even faster. The last major step in the evolution of the ribosome was the addition of its proteins.

The most practical way to test Bokov and Steinberg's hypothesis will be to build the intermediate ribosomes and see if they work as predicted. But perhaps we should not give up on nature just yet. As I have reported, RNA-based life could conceivably still be hiding in refuges somewhere here on Earth, eking out an existence with ribosomes that are a little less hideous than our own.

—Carl Zimmer

Don't miss the chance to check on what happened at the annual meeting of AAAS this past weekend at Findings. In just a few busy days, researchers squeezed in discussions on everything from the evolution of kissing to the genetics of dog shape. There were talks on Neandertals and hobbits, even a science dance contest. Also, hear about the origins of emotions or the origins of the human diet in podcasts.

Science writer and author of Microcosm: E. coli and the New Science of Life Carl Zimmer wrote the "On the Origin of Life on Earth"  last month. Today he discusses evolution on other worlds.

Imagine you spent your whole life on a tiny island, with only some tortoises and snails to give you a clue to what life was like. You'd be forgiven for failing to imagine a Venus flytrap or an armadillo. Evolutionary biologists are in much the same bind. They are, for the time being, stuck on a planetary island, only able to study life on Earth. While life on Earth takes many forms, every living thing is nevertheless a variation on the common theme of DNA, RNA, and protein. What kind of life, if any—exists on other planetary islands we don't know?

If we do discover life someday on another planet, evolutionary biology would leap to a new level. Biologists would be able to compare how evolution played out on two separate planets. If life began independently on another world and ended up a lot like life on Earth, that might mean that evolution must follow certain rules no matter where on the universe it plays out. Or perhaps evolution has the potential to be a lot weirder than we know, because we're stuck here on our little island of life. The closest place where it makes sense to look for life is Mars. Its surface may have been warm and wet in the past, and puffs of methane discovered in recent years just might be a sign that microbes are still thriving deep under the surface. The best way to see if that's the case is to drill into the Martian soil and find them.

But Chris McKay of NASA warns in this week's Science that in our search for a second biosphere, we may contaminate it with our own. As McKay points out, space scientists were already concerned about contaminating other planets in the 1960s. NASA completely sterilized the Viking Probe that landed on Mars in 1976, but the results of that mission suggested that the Red Planet was so harsh that no life could survive and so fewer protections were necessary. The Mars rovers that we've all watched wandering across the Martian landscape probably brought hundreds of thousands of bacteria with them.

Yet, over the years, scientists have grown more concerned again. The surface of Mars is clearly an awful place for even the hardiest microbe. But if we start drilling down into the ground, we might well be injecting microbes from Earth down into a Martian ecosystem. We unfortunately know all too well what happens when we accidentally introduce species to new places. At worst, the new species becomes invasive and drives native animals and plants extinct. At best, native ecosytems are dramatically altered. Do we have an ethical obligation to protect what McKay called "indigenous biospheres"?

Later this year, a meeting will be held to consider just this question. We do need to take responsibility for our actions, but we also should not forget another lesson of evolution here on Earth: Invasive species don't always need people to deliver them to a new home. Darwin himself first recognized that seeds and eggs can been carried to distant islands on the feet of birds. In space, meteorites may act as interplanetary birds, bringing microbes from Earth to Mars—or perhaps the other way as well. Even if we take every possible precaution, the life we find on Mars may turn out to be invasive after all. It just invaded Mars a billion years ago.

—Carl Zimmer

Arizona State University joins in the global celebration of Darwin‘s 200th birthday, and commemorates the 150th anniversary of the publication of On the Origin of Species, with Darwinfest—a celebration of how the expression of radical thinking and scientific and technological enterprise can and has changed the world.

Why does Darwin matter? Arizona State University takes that question to students and the public in Arizona 4 to 13 February with core events that capture how Darwin’s bold thinking has evolved into new understanding about some of the most fundamental questions about humanity and the human spirit, including our origins and life beyond Planet Earth.

See the full calendar of events and information for details.

Events include:

· Origins Symposium (3-6 April)

· The Darwin Distinguished Lecture Series (through November 2009)

· The Future of Evolution Lecture Series (4-25 February)

· Looking for Life: Adventures and Misadventures in Species Exploration (11 February)

· Darwin Days (4-13 February) with a Tea Party and Darwin Look-alike Contest

 

—Margaret Coulombe

Coordinator, ASU Darwinfest.

480...

Arizona State University, Tempe

Stephen J. O'Brien is chief of the Laboratory of Genomic Diversity at the National Cancer Institute in Frederick, Maryland. He spoke last week at the U.S. National Academy of Sciences Sackler colloquium on evolution, Two Centuries of Darwin, and came away with these thoughts.

There are few science paradigms that survive and continue their influence for very long—most disappear within a decade. So it was a remarkable gathering at the Beckman Center of the National Academies of Science and Engineering in Irvine, California (hosted by John C. Avise and Francisco J. Ayala), where a group of eclectic evolution experts—biologists, philosophers, thinkers, historians, and empiricists—met to reflect upon 150 years of influence exerted by On the Origin of Species and the 200th birthday of its author, Charles Darwin. In 17 brilliant and colorful lectures, we heard updates, details, and advancements centered on nature’s examples of natural selection and two carryover concepts that intrigued Mr. Darwin: artificial and sexual selection. The historians and philosophers revealed timeless insights into the prescience of Darwin's logic and dismissed as rubbish conspiracy theories that imply he purloined ideas from Alfred Russel Wallace. Francisco Ayala marveled at Darwin's propensity to erect hypotheses over any biological observation and then to begin the scientific process of falsification (or validation) a century before granting bodies began to instruct us to follow this format in our research proposals. Elliott Sober reminded us that adaptive characters offer evidence of their cause, natural selection, while nonadaptive or even maladaptive characters are better for imputing common ancestry. Adaptation happens frequently, leading to parallel, independent origins of flight and of aquatic and terrestrial locomotion, but neutral traits form the currency for modern coalescent and phylogenetic reconstructions. Darwin’s rough sketch of a bifurcating tree of life connecting related species was shown often to remind us that temporal transition of species is a continuous branching process that continues today.

With but 17 talks, the speakers’ examples proved but a snippet of the possible richness of study and empiricism that the Origin has since spawned; indeed, a score of Darwin's birthday celebration symposia scheduled this year across the globe testify not only to the expansiveness of evolutionary theory and practice to all corners of biology but also to its critical role as a bedrock in modern biology, from medicine to agriculture to natural history and ecology. Rich, natural illustrations of sexual selection in beetles and small terrestrial, aquatic, and marine critters affirmed the notion that there are countless discoverable strategies for how to proliferate and survive in our world. Darwin perceived artificial selection of domesticated animals and plants by human agency as providing a cogent natural laboratory example of how selection can change things. And change things it did: When Neolithic farmers in the Near East set up the first villages and communities, domestic species were chosen and selected almost simultaneously. Some believe this event changed the world enormously, providing a ready food supply, clothing, servile labor, sport, transport, and even home companions. Charles Darwin saw domestication as a validation of the force of natural selection, while others see it as the lever by which civilization overtook the globe in so short an interval.

Pause to consider the influence of evolutionary theory and practice, the Darwinian Revolution, as Michel Ruse termed it, made us remember how much it really changed science. Darwin’s genius was not only deductive and empirical; he was also a master communicator, the Abraham Lincoln of his day. His ideas were understood clearly and embraced widely despite the cacophony of theist protestations. His image appears on the 20-pound English note; his legacy is celebrated in a three-story marble mural of his notebook in Beijing; and academic departments of evolutionary theory and practice flourish in the world’s universities to inform us of the intricacies of the process in the era of DNA sequencing and genomics. I wish I could have known Mr. Darwin, but instead, perhaps I should simply try to attend all the celebrations of his theory and influence now, so many years since his birth.

—Stephen J. O'Brien