Origins

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

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

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.

All this neural circuitry gives octopuses exquisite control over their bodies, including some nifty tricks for evading predators, and it has even prompted speculation about cephalopod consciousness.

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

 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 John Travis

Creation, the star-studded biopic of Charles Darwin, opens later this week in the United Kingdom, and scientists and science educators have been bemoaning the fact that the film doesn’t yet have a U.S. distributor. Although the production company behind the movie has hinted that a U.S. deal is imminent, some have suggested that the movie, in which fellow naturalist Thomas Huxley joyfully tells Darwin he has “killed God,” is too controversial to sell in America, where disbelief of the theory of evolution remains strong among religious conservatives. Eugenie Scott, executive director of the National Center for Science Education, even sent out a letter encouraging a lobbying effort on the film’s behalf. Noting that she had seen and liked the movie, she wrote: “But I worry (and can only speculate) that the difficulty the producers have had getting a US distributor might reflect corporate nervousness about getting an audience for a topic that deals with evolution. 'Creation' is definitely honest about Darwin's religious skepticism. The big middle part of America that we are aiming at will see a complex character with a lot of reasons to doubt the Christian pieties spouted by the minister character in the movie.”

From a cinematic standpoint, however, it’s not clear that Creation deserves the fervent support of the scientific community. In a nutshell, the movie, based on the book Annie’s Box, depicts a midlife Darwin at home in an idyllic English village dealing with the grief of his daughter Annie’s recent death and trying to write On the Origin of Species, the book that would make him a household name. The film has many historical inaccuracies, but that’s to be expected when filmmakers condense a life into a few hours. Creation’s larger problem stems from the decision to focus on a narrow slice of Darwin’s life, arguably one of the least interesting.

According to the movie’s press material, the film portrays the “powerful story of Charles Darwin and the single most explosive idea in history. … In Creation, the battleground is a man’s heart. Torn between his love for his deeply religious wife and his own growing belief in a world where God has no place, Darwin finds himself caught in a struggle between faith and reason, love and truth.” What this ultimately means is that the movie centers on why Darwin was so slow to publish On the Origin of Species, attributing the delay to his illness, his grief, and his desire not to offend the world, or at least his wife. In other words, instead of dramatizing how Darwin traveled the world and arrived at the most explosive idea in history, Creation is ultimately about the world’s biggest case of writer’s block.

That’s a flawed choice, especially when one has stars as talented as Paul Bettany and Jennifer Connelly playing the Darwins. Married in real-life, the pair bring a natural, loving chemistry to the well-acted roles (Connelly may need to seek out more ambitious and different roles, however; here she plays the beautiful, supportive wife of a tormented genius who sees things, an almost identical role to the one she had in A Beautiful Mind, the story of Nobel prize-winning mathematician John Nash).  And there’s little question that Creation is beautifully and at times inventively filmed. One scene nicely exploits computer-generated graphics to show how the tragedy of death in nature is necessary for life to continue.

The film periodically tries to suggest the scientific methodology Darwin used, although highlighting his grisly preparation of pigeon skeletons may more likely turn some viewers' stomachs than explain his study of natural variations within species. As Scott notes, the film does reveal a more “complex” picture of Charles Darwin, one that may shock those used to the genius stereotype. The film depicts the celebrated naturalist as a young man so ravaged by depression and illness—whether real or imagined remains a matter of debate; a recent book labels Darwin a hypochondriac—that he avails himself of a quack Victorian water remedy. He’s also seen taking unknown medicinal drugs and hallucinating the ghost of Annie, with whom he discusses his doubts and to whom he relates some of his life’s adventures and scientific undertakings. For example, one interlude shows Darwin studying a captured orangutan, an episode that presumably helped lead to his book The Expression of the Emotions in Man and Animals. But given that he’s telling stories to an apparition, it’s hard for viewers to evaluate how these tales allowed Darwin to form his pioneering ideas. And given that the ghost itself is a creation of the filmmakers’ minds, some viewers may wonder if they can trust the veracity of anything in the movie. As for the topic of science and religion, the movie’s approach would please Richard Dawkins in that it doesn’t offer a middle ground in which one can believe in both evolution and God. Such a compromise would ruin the drama of Darwin’s struggle it seems.

What’s missing in Creation is enough insight into what enabled Darwin to bring together disparate information into a powerful story of how nature works. His daughter is bright and insatiably curious, and presumably a proxy for Darwin the researcher, but the father offers little evidence of being a fountain of brilliant insights. After all, in the movie, his theory is already a fait accompli; he just needs to write it up for publication. While much of the movie is about Darwin trying to get past his grief and illness, in the end it’s only the threat of competition—a letter from Alfred Russell Wallace—that forces him to overcome his writer’s block. And then the filmmakers would have you think that Darwin allowed his wife to decide whether the work should be published. One wishes the script had gone through a few more generations of evolution.

Creation trailer:

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.

by Virginia Morell

Birds are noteworthy not only for their wit, charm, and sartorial splendor but also for their great dancing. So, for its contribution to this year’s Darwin celebrations, London’s Rambert Dance Company is putting on a bird-inspired show.

The company has the ideal scientific adviser: Nicola Clayton, an expert on the cognitive talents of jays and crows at the University of Cambridge and a lifelong dancer. Clayton helped the company’s artistic director, Mark Baldwin, come up with a program that she calls a “distillation of Darwinian ideas about evolution, particularly sexual selection.” One dance, for instance, is inspired by the elaborate displays of the six-plumed bird of paradise. In the wild, males inflate “a tutu” of feathers, then vigorously shake their heads and necks while sliding across a stage—all while being critically observed by a gallery of females. “The males are so constrained in their movements by female choice that it’s comical,” says Clayton. Other dances in the program evoke blue manakins and bee hummingbirds.

The show, titled The Comedy of Change, runs 16–19 September at the Theatre Royal in
Plymouth and 3–7 November at Sadler’s Wells in London.

University of Cambridge has produced a video about Clayton's research and the dance.

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