If you're tired of watching It's a Wonderful Life or A Christmas Carol yet again, perhaps Darwin can occupy your cold winter nights. As a holiday treat, Origins would like to point out that this summer's Darwin Festival in Cambridge, U.K., has compiled videos of many of its sessions, which typically start with a reading from Darwin's correspondence. You can watch the videos directly here on the embedded media player, even skipping among the talks, or go to where they are posted here on YouTube. Enjoy.
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December 18, 2009
December 9, 2009
by Elizabeth Pennisi
In my essay on the origin of flowering plants, I discussed many ideas related to how angiosperms came to dominate terrestrial ecosystems. Representing hundreds of thousands of species and 96% of all terrestrial vegetation, flowering plants are the most successful land plants on Earth. Researchers have long chalked it up to their flowers, which enlist insects and other animals to help them reproduce and spread. But two plant biologists credit the leaves instead. More leaf veins (left) made the plants better photosynthesizers, say Timothy Brodribb, a hydraulic physiologist at the University of Tasmania in Australia, and Taylor Feild, now at the University of Tennessee, Knoxville. "The importance of vein density has never before been so clearly presented," says Peter Wilf, a paleobotanist at Pennsylvania State University, University Park. Read about their compelling data and argument here.
Credit: Timothy Brodribb
November 24, 2009
by Michael Balter
NEW YORK CITY—The exhibition of Vermeer’s The Milkmaid at the Metropolitan Museum of Art here is scheduled to end on 29 November, but don’t worry if you can’t get to the Big Apple in time to see that famous Old World painting. Just around the corner, New York University’s (NYU's) Institute for the Study of the Ancient World (ISAW) opened a stunning free exhibit* of more than 250 Old World artifacts on 11 November. These arts and crafts works from Europe’s Danube Valley are a bit older than Vermeer’s 17th century masterpiece, however: They date from 5000 to 3500 B.C.E., when farming was spreading into Europe from the Near East and the mobile, hunter-gatherer lifestyle was giving way to a sedentary, village-based existence.
The exhibit is a coup for ISAW, which was founded in 2006 amid considerable controversy. (The institute was made possible by a $200 million gift from donors Leon Levy and Shelby White, who were also collectors of ancient artifacts; some archaeologists believe that their collection has included looted objects.) The spectacular artifacts now on display, on loan from more than 20 museums in Romania, Bulgaria, and Moldova, have never been exhibited before in the United States. They feature dozens of terra-cotta figurines that some archaeologists have interpreted as “mother goddesses,” including a so-called Council of Goddesses from the site of Poduri-Dealul Ghindaru in Romania (see photo above), consisting of 21 small figurines and the tiny chairs some of them apparently sat on. The detailed and helpful explanatory legend, typical of the others in this exhibit, points out that the goddess interpretation is debatable, and that other hypotheses—for example, that the objects were dolls or playthings—must be considered.
Also on display is a pair of fired-clay figurines, including one called The Thinker, from the necropolis of Cernavodă in Romania, found in 1956 and dated to between 5000 and 4600 B.C.E. (shown at left). And the exhibit includes some of the more than 3000 gold objects from the Varna cemetery in Bulgaria, the richest burial ground in ancient Europe, dated to about 4500 B.C.E. The cemetery, discovered in 1972, provided important evidence that early European farming societies were not egalitarian as many archaeologists had assumed: The gold scepters, diadems, bracelets, necklaces, and animal heads were found in only 62 of the 310 graves, and the richest finds were restricted to only four—strongly suggesting that these communities were hierarchical.
The exhibit continues until 25 April. But if you miss it—or if you live today in Old Europe—the show moves to the Museum of Cycladic Art in Athens in October 2010.
*The Lost World of Old Europe: The Danube Valley, 5000-3500 B.C., Institute for the Study of the Ancient World, 15 East 84th Street, New York, NY 10028.
Set of Twenty-one Figurines and Thirteen Chairs: Elena-Roxana Munteanu/Neamţ County Museum Complex, Piatra Neamt
The Thinker and Female Figurine from Cernavodă: Marius Amarie/National History Museum of Romania, Bucharest
November 24, 2009
The National Science Foundation has released an online special report on the influence of Charles Darwin on many walks of science. Evolution of Evolution: 150 Years of Darwin's On the Origin of Species features essays, videos, and podcasts from prominent researchers, as well as a timeline of advances in evolution, all beautifully crafted to enchant anyone curious about the history of life. Special topics cover anthropology, biology, astronomy, polar sciences, and geosciences, as well as Darwin.
Image credit: Illustrations by Nicolle Rager Fuller, National Science Foundation (background and center); © 2009 JupiterImages Corp. (top right); NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team (bottom )
November 6, 2009
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
November 4, 2009
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)
November 2, 2009
by Elizabeth Pennisi
Charles Darwin worked hard to figure out how cooperation within a species—self-sacrifice among worker bees, for example—could have evolved. But he was stumped when it came to understanding cooperation between species. In his book, On the Origin of Species, he wrote, “Natural selection cannot possibly produce any modification in a species for the good of another species.” If that could be proved to have happened, “it would annihilate my theory, for such could not have been produced through natural selection.” And he scoffed at supposed examples perpetuated by some natural historians, such as a rattler using its rattle to warn prey. “I would almost as soon believe that the cat curls the end of its tail when preparing to spring, in order to warn the doomed mouse.” Instead, he argued that the rattle was meant to scare off birds and other potential predators.
Nonetheless, countless examples of cooperation between species exist—albeit many perhaps outside Darwin’s knowledge. Many long-standing partnerships are strengthened by specialized structures or traits in one species that benefit the other. Many of these relationships are dynamic, shifting back and forth over evolutionary time between exploitative and mutualistic.
Take the ant plants and their ants (see left). In tropical forests, certain types of trees make a home for ants that inhabit them, providing hollow stems or leaf pouches where the insects can roost and raise young. In return, the ants keep hungry herbivores at bay and sometimes kill off surrounding vegetation, creating a clearing around the trees.
Nineteenth century naturalists fiercely debated whether these ants forced their way into trees as parasites, wounding trees to make their nests, or whether they had a more benign relationship with the plants they lived in. In 1873, botanist Richard Spruce likened the ants to fleas on a dog—a nuisance. But others contended that some plants, acacias in particular, provided hollow thorns and food rewards to keep ants around for protection from herbivores. Many studies have supported this hypothesis over the past 4 decades. It seems the ants bite and poison surrounding vegetation, reducing the competition for space, water, and sunlight.
In the November issue of American Naturalist, David Edwards of the University of Leeds, U.K., and his colleagues describe how sometimes these ants get carried away. “I think most [researchers] believed that ants’ relationship with their host plants had been pretty well defined,” says John Tooker, a chemical ecologist at Pennsylvania State University, University Park. But in 1996, scientists observed a new, peculiar ant behavior. While exploring the jungles of southeastern Peru, a team of ethnobotanists came across a number of "devil's gardens," what many locals call the ant-made clearings around trees. Although they had seen such clearings before, the researchers were surprised by what the natives showed them next: Trees of other species on the outside of the clearing were scarred and swollen (see right) with networks of cavities filled with worker ants, queens, brood, and mealy bugs. "These galls made up a large percentage of the swollen trunk volume," says Edwards. Sometimes the internal excavations were so extensive that the tree had collapsed. The locals blame the scars on forest spirits.
The researchers think the ants are attacking these other trees because there aren’t enough ant plants to house ever-expanding colonies. “It suggests a level of ecosystem engineering [by the ants] not previously recognized,” says Tooker. And at this point, the relationship seems anything but mutual. “I expect this to be an antagonistic relationship because of the range of tree species that are galled by the ants,” Tooker notes. These are trees not typically associated with ants, and so there’s been little opportunity for a partnership to evolve. But if the ants patrol the area and ward off herbivores, then perhaps there is some payback by the ant to the tree, he adds.
The ants involved belong to the genus Myrmelachista, which typically nest in stems. Some species in the genus do not form associations to particular species, says John Longino, an entomologist at Evergreen State College in Olympia, Washington. He suggests that devil’s garden ants coevolved with new queens, gradually evolving a preference for certain plant species as the best nesting spots. Their targets eventually provided housing rather than chance having irregular holes chewed into their stems. Then, “perhaps it doesn’t take much to turn a mild-mannered and inconspicuous stem-nesting ant into a ferocious devil’s gardener. Maybe just the right kind of plant can encourage and manipulate those latent talents,” he says.
These enticements can lead to trouble, however, as Edwards's collaborator, Megan Frederickson of the University of Toronto in Canada, has discovered. Ever in need of more room, the ant Allomerus octoarticulatus takes a devious step to promote its host tree’s growth. It destroys any flower buds that the host produces. When Frederickson measured the growth rates of sterilized and reproductive plants, she found that the ant’s drastic maneuver did encourage more vegetative growth—and more living space for the ants. She reported those findings in the May issue of American Naturalist.
Darwin did not have the benefit of these experiments that show reciprocated benefits and the dynamic balance between giving and taking. But if he had, “he would have found ant-plant symbioses a real hoot,” says Mike Kaspari, an ecologist at the University of Oklahoma, Norman.
Photo credits: (ants) Megan Frederickson; (tree) Douglas Yu
October 23, 2009
by Greg Miller
Cephalopods—octopuses, squid, and their relatives—ruled the seas in the Cambrian era, some 500 million years ago. But their world changed in a big way with the Cambrian Explosion, a rapid diversification of life on Earth that included the origin of fish. Suddenly, cephalopods had new opportunities—delicious fish!—and their first serious competition and potential predators. They had to get smart in a hurry.
So it’s no wonder then that modern cephalopods have the most complex brains of any invertebrates. An octopus brain (lower, right) has 50 to 75 lobes and at least as many neurons (about 100 million) as a mouse brain (lower, left). And that’s not counting the smaller "brains" in each arm and the still smaller "brains" (ganglia, technically) associated with each sucker.
Although the octopus brain rivals the size and complexity of many vertebrate brains, its architecture differs dramatically. “Short of martians showing up and offering themselves up to science, cephalopods are the only example outside of vertebrates of how to build a complex, clever brain,” says neuroscientist Cliff Ragsdale of the University of Chicago in Illinois. For that reason, Ragsdale says, these creatures have much to teach us about brain evolution.
Ragsdale and his postdoctoral fellow Shuichi Shigeno are investigating whether the neural circuits that control movement, memory, and other functions in an octopus brain work the same way as do the analogous circuits in other animals. The British zoologist J. Z. Young did early work on octopuses in the 1960s, mapping out their brain anatomy and ablating individual lobes to investigate their contributions to behavior. But as of yet, Ragsdale says, no one has brought modern molecular methods to bear on these questions.
That’s what Shigeno has begun doing. At the Society for Neuroscience annual meeting in Chicago earlier this week, he presented preliminary findings from a series of experiments that investigated gene expression in the developing brain of Octopus bimaculoides, a small octopus that inhabits mud flats along the southern California coast. Shigeno found that several genes with well-known roles in patterning “lower” brain regions such as the brain stem and spinal cord in mice are expressed in a similar pattern in the developing octopus brain.
Genes involved in the development of “higher” brain regions in mice, on the other hand, showed more diverse patterns in the octopus brain. Genes expressed in the mouse hypothalamus, an area that regulates sleep and appetite, among other functions, also showed up in a lobe of the octopus brain thought to perform analogous tasks. But genes expressed in the mouse hippocampus and cerebral cortex, although also expressed in the octopus brain, had a distribution that bore little resemblance to their distribution in mice. To Shigeno, the findings suggest that lower levels of the octopus brain may be wired much like the analogous circuits in the vertebrate brain, but higher levels may show more divergence from the vertebrate wiring diagram.
Ragsdale agrees, but he cautions that such studies of gene expression tell only part of the story. He and Shigeno already have other experiments in the works to map out neural circuits in the octopus brain more directly and to study the neurochemistry of neurons in areas such as the hypothalamus analog to see if they secrete the same signaling peptides as do hypothalamic neurons in other animals. “We have a lot to learn about these animals,” Ragsdale says.
Photo credits: Cliff Ragsdale and Suichi Shigeno
October 1, 2009
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
September 29, 2009
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