Origins

Scientists use the “molecular clock”—an estimated rate of DNA mutation—to date key events such as migrations and the divergence of species. But just how accurately the clock keeps time has long been debated. A new study of living and ancient Antarctic penguins, like those on Ross Island at left, suggests that DNA mutates six times faster than predicted. That could mean that some species—such as chimps and humans—could have split off from each other much more recently in time than previously thought. The finding should help improve the dating of relatively recent events, including when people domesticated various crops and animals, and when major human migrations occurred.

To use the molecular clock, scientists estimate the rate of mutation in DNA, estimating that the mutations occur in a steady, clocklike manner. For example, if a gene accumulates changes at a rate of five every 1 million years, 25 mutations in a genetic sequence would mean that the sequences had diverged 5 million years ago. The technique has been used to estimate when humans separated from the other great apes, to estimate the arrival of people in the Americas, and to create evolutionary trees for many species. Molecular clocks are usually calibrated by using the age of a known species from the fossil record. But scientists disagree about the speed or rate at which mutations occur and under what circumstances the rate is influenced by natural selection or other factors.

To see just how accurate molecular dating is, David Lambert, an evolutionary biologist at Griffith University in Queensland, Australia, and colleagues looked at Adélie penguins. These Antarctic birds may be the best species yet for building an accurate clock, the team argues, because scientists can study the genetic sequences of both living and ancient members of the species. The penguins generally return each year to the same nesting ground; thus, each rookery can have layers of bones dating far back in time. Indeed, the birds have nested at some rookeries for 44,000 years. "You can take blood samples from the living penguins and then literally collect the bones of their ancestors" in the ground below, says Lambert, because the penguins usually return to their natal colony to mate. Other studies usually can only compare genes from organisms separated in time by millions of years. 

Using modern blood and ancient bone samples, the researchers extracted the entire mitochondrial genome from 12 modern and eight ancient penguins, including two that were dated to 44,000 years ago using radiocarbon methods. They then compared the mitochondrial DNA of the living penguins with the ancient ones to determine the number of mutations that had occurred. Because they had radiocarbon dates for the ages of the ancient penguins, the scientists could accurately measure the bird’s average mutation rate, ultimately calculating that its mitochondrial genome had evolved at a rate two-to-six times faster than previously estimated.

The team's findings, reported in this month’s issue of Trends in Genetics, support similar results for faster clocks in mitochondrial sequences in cattle. But in this new study, the researchers succeeded in calculating the rate of mutation within almost the entire mitochondrial genome, providing “more conclusive evidence,” for a rapidly ticking clock, says Dee Denver, an evolutionary biologist at Oregon State University in Corvallis and one of the paper’s co-authors. They also focused on a region of the genome that is known to not be influenced by natural selection, they write in the paper. Thus, they say that the resulting clock is not merely a reflection of penguin evolutionary history and can be applied to other species.

"It's novel and groundbreaking work," says Mark Hauber, an evolutionary biologist at Hunter College in New York City, who was not affiliated with the study. "It's a significant discovery," adds Elizabeth Matisoo-Smith, a biological anthropologist at Otago School of Medical Sciences in Dunedin, New Zealand, who expects it will help resolve several discrepancies between genetic data and the archaeological record, such as the peopling of the Pacific Islands and the Americas. However, the penguins’ rapid clock "should be confirmed on a wide diversity of species" before being adopted as the new standard, says Robert Wayne, an evolutionary geneticist at the University of California, Los Angeles.

Photo credit: Euan Young

by Elizabeth Culotta

In my essay on the origin of religion earlier this month, I describe new research tackling the question of how belief in unseen deities arose. One leading model from cognitive science suggests that religion is a natural consequence of human social cognition and that we are primed to see the work of another thinking being—an agent—in the natural world and our lives. But a person of faith might give a different kind of answer: Religion arose because divinity exists, and belief in deities represents the human response to it.

Does the cognitive science model conflict with that religious perspective? Some creationists find the research an attack on faith. But the scientists I interviewed said that the question of whether God exists is distinct from their research. For example, Deborah Kelemen of Boston University, whose psychological studies have found that children and adults have a natural penchant for creationist explanations, says that her work “does not speak to the existence of God; it speaks to why and how we might believe. Whether God exists is a separate question, one we can’t scientifically test.” Those who are upset by the idea that human minds are likely to construct gods, or that evolution has shaped religion, “are misreading the message of this work,” she says.
 
Charles Darwin neatly articulated the distinction between studying the mechanism of religious belief and its truth. When considering the origin of religion in The Descent of Man, he wrote: “The question is of course wholly distinct from that higher one, whether there exists a Creator and Ruler of the universe; and this has been answered in the affirmative by some of the highest intellects that have ever existed.” (He did not, however, report how he himself stood on the question of God’s existence.)

Some scientists say that the cognitive model of religion is compatible with belief in God. The science explains why humans are receptive to religion, a notion that theologians of various religions have explored, says Justin Barrett of the University of Oxford in the United Kingdom, who studies the psychology of belief and is an observant Christian. “Embedded in all of us is a receptiveness to the idea of transcendence—an idea you see in many of the world’s religions. From their point of view, we trot out the scientific evidence for this receptiveness, and their response is, ‘Yeah, right, we knew that,’ ” says Barrett.

Barrett and others do sometimes get letters from angry believers, but they also receive letters from irate atheists, who don’t buy the notion of religion as part of human nature. “I’m not seen as a friend of atheists either,” says Jesse Bering of Queen’s University, Belfast. “I’m arguing there are no atheists proper.”

All the same, some scientists do see a potential conflict between the cognitive research and faith, if researchers one day find that belief in God stems from trivial or untrustworthy psychological reasons. “The study of why people believe in God can shed light on whether they do so for a good reason or a bad reason,” says Paul Bloom of Yale University. “If I were religious, this would matter to me a lot.”
 

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

Every human society has had its gods, whether worshiped from Gothic cathedrals or Mayan pyramids. In all cultures, humans pour resources into elaborate religious buildings and rituals. But religion offers no obvious boost to survival and reproduction. So how and why did it arise? In my Origins essay this month, I follow two very different disciplines—archaeology and cognitive psychology—as they attempt to understand this puzzle.

To Charles Darwin himself, the origin of belief in gods was no mystery. “As soon as the important faculties of the imagination, wonder, and curiosity, together with some power of reasoning, had become partially developed, man would … have vaguely speculated on his own existence,” he wrote in The Descent of Man. In the past 15 years, a growing number of researchers have followed Darwin’s lead and explored the hypothesis that religion springs naturally from the normal workings of the human mind. This new field, the cognitive science of religion, draws on psychology, anthropology, and neuroscience to understand the mental building blocks of religious thought. “There are functional properties of our cognitive systems that lean toward a belief in supernatural agents, to something like a god,” says experimental psychologist Justin Barrett of Oxford University.

Barrett and others see the roots of religion in our sophisticated social cognition. Humans, they say, have a tendency to see signs of “agents”—minds like our own—at work in the world. “We have a tremendous capacity to imbue even inanimate things with beliefs, desires, emotions, and consciousness, … and this is at the core of many religious beliefs,” says Yale psychologist Paul Bloom.

Meanwhile, archaeologists seeking signs of ancient religion focus on its inextricable link to another cognitive ability, symbolic behavior. They too stress religion’s social component. “Religion is a particular form of a larger, social symbolic behavior,” says archaeologist Colin Renfrew of the University of Cambridge, U.K. So archaeologists explore early religion by excavating sites that reveal the beginnings of symbolic behavior and of complex society.

These fields are developing chiefly in parallel, and there remains a yawning gap between the material evidence of the archaeological record and the theoretical models of psychologists. Yet there have been some stirrings of interdisciplinary activity, and all agree that the field is experiencing a surge of interest and new evidence, with perhaps the best yet to come.

Illustration credit: Katharine Sutliff/Science

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

Human evolution research is not for the faint-hearted. Hominin fossils are rare and hard to find. And more often than not, no sooner do anthropologists announce a big discovery than other researchers argue that they have it wrong. The next chapter in such a scenario unfolded last week, when scientists attending a meeting* at the Royal Society in London resurrected a debate about a single, crucial hominid specimen: a 3.5-million-year-old cranium named Kenyanthropus platyops—“the flat-faced man of Kenya” (shown at left).

Discovered in 1998 by a team including paleontologists Meave Leakey of the National Museums of Kenya in Nairobi and Fred Spoor of University College London, K. playtops suggests a greater degree of diversity in the human family tree than previously suspected: two species of hominids, not one, in the crucial period between about 4 million and 3 million years ago. That’s the time of Lucy, Australopithecus afarensis, whose lineage is thought by many to have given rise to our own genus, Homo.

But there was one nagging problem: The Kenyanthropus cranium, discovered west of Kenya’s Lake Turkana, was cracked and distorted, making it possible that some features that set it apart from A. afarensis—including its flat face and tall, vertically oriented cheek bones—could be artifacts. Paleoanthropologist Tim White of the University of California, Berkeley, argued in a 2003 Perspectives in Science that K. platyops probably fell within the range of variation among known A. afarensis fossils and might simply represent an “early Kenyan variant” of that species.

In London, Spoor responded to such arguments with a new, detailed study. He concluded from computed tomography scans that the upper jaw, or maxilla, had suffered much less distortion than the rest of the cranium. So he focused on that bone, correcting for the distortion present. He measured distances among several “landmarks” on the maxilla, including the point at which the cheekbone attaches to it, the extent of its forward projection, and the orientation of its tooth sockets. He used the same landmarks on A. afarensis specimens, the roughly 4-million-year-old A. anamensis, later australopithecines, and modern humans, chimps, and gorillas. Then he crunched the measurements in a computer-assisted analysis called principal component analysis to reveal the variability among the specimens. The result: Kenyanthropus fell cleanly outside the range of variation in all the other samples. “Species diversity existed at 3.5 million years ago, and this justifies assigning a new taxon,” Spoor concluded.

But White, who was present and has long argued that there is no evidence for more than one lineage of hominids at this time, wasn’t convinced. When the talk was thrown open for discussion, White took the microphone and began firing questions at Spoor about the degree of variation of the cheekbone position among specimens of A. afarensis and other hominin species. “We took that into account,” Spoor responded, “and I just showed you a graph” about it. “I didn’t ask you whether you took it into account; I asked you what it was,” White said. Spoor, clearly frustrated, told the audience that he had no vested interest in this debate. At that point, the session chair interrupted and invited everyone to break for coffee, but Spoor and White continued to debate between themselves for the next half-hour.

Spoor’s study, like the others presented at the meeting, will be published in the Philosophical Transactions of the Royal Society B: Biological Sciences in Spring 2010. When it is, the debate will no doubt continue.

*The First 4 Million Years of Human Evolution, London, 19-20 October 2009.

Photo credit: F. Spoor, copyright National Museums of Kenya

by Michael Balter

LONDON—When Tim White of the University of California, Berkeley, agreed to speak at a human origins meeting^* at the Royal Society here, he sent no abstract and provided only a one-word title: “Ardipithecus.”

But that one word was enough to earn him a spot on the podium and a prominent role at the meeting. After 15 years of study, White and his colleagues have just published their massive, 108-page report on Ardipithecus ramidus, at 4.4 million years the oldest partial skeleton of a putative human ancestor (see the Science special issue of 2 October, cover at left). The 2-day meeting marked White’s first in-person presentation of Ardipithecus to a roomful of independent researchers; co-author anthropologist C. Owen Lovejoy of Kent State University in Ohio also made the trip. Their emphasis on Ardi’s non-apelike features, however, drew a tart response from some primatologists in the room.

The roughly 50-kilogram female, which the Ardipithecus team concludes walked upright although it also spent time in the trees, has a decidedly un-chimplike anatomy. White and colleagues therefore have asserted that living apes are not good models for understanding the last common ancestor (LCA) of humans and chimpanzees—a claim that has stung many primatologists. “I assumed … chimps might be helpful in tackling the challenges of human evolution,” said chimpanzee expert William McGrew of the University of Cambridge in the United Kingdom. But after Ardi, “all this chasing after chimpanzees was deemed to be irrelevant” to human evolution. McGrew, the first speaker, challenged a statement in one of the papers in Science that “no modern ape is a realistic proxy for characterizing early hominid evolution—whether social or locomotor.”

White, Lovejoy, and their colleagues base this conclusion on many features of Ardi’s postcranial anatomy. Although some researchers had assumed that the LCA had arms adapted for swinging in the trees and walked on its knuckles like chimps, A. ramidus lacks these and many other features possessed by modern apes such as chimps and gorillas. The team argues that Ardi’s anatomy suggests that its behavior and social structure also differed from that of modern chimps. For example, one of the papers, authored by Lovejoy, suggests that A. ramidus males were probably much less aggressive toward each other than chimp males are and that they pair-bonded with females.

McGrew told the attendees that although he agreed that “the LCA was not a chimpanzee,” the behavior of living chimps such as those at left can still inform hypotheses about the LCA’s behavior. McGrew listed the considerable evidence for chimp behaviors that possibly mirror those of extinct and modern humans, such as the use of complex tools, aiming and throwing objects, the construction of sleeping nests or platforms, and evidence for considerable spatial cognition such as the ability to remember the locations of thousands of trees in a forest. At least some of these behaviors, McGrew said, are shared by chimps and modern humans because they have deep evolutionary roots. “So to hypothetically credit the LCA with the ability of [chimps] is not unreasonable,” McGrew concluded. 

At the end of the day, when the meeting was thrown open for discussion among the roughly 200 attendees, White countered McGrew’s argument, pointing to what he saw as the dangers of using a chimp model for the LCA’s behavior. “If we try to model the LCA or even the earliest hominids based on living chimps, which have these adaptations to [swinging in the trees], to moving through that canopy so well and so quickly that they can take down a red colobus monkey, we could be very misled. Ardipithecus probably couldn’t do that, and the LCA probably couldn’t do that.” 

Yet White says he’s not trying to toss out all chimp research. “The fact that a few highly derived descendants managed to survive until today obviously enhances our appreciation of their evolution,” he told Science. “It also provides perspective on ours. The study and conservation of chimpanzees and bonobos are surely justifiable on their own merits, even though [early] hominid skeletal anatomy, behavior, and ecology do not match those seen now in these specialized persistent ape lineages.”

And Carol Ward, a paleoanthropologist from the University of Missouri School of Medicine in Columbia, points out that White and Lovejoy “aren’t saying that [studies of] chimps aren’t useful but that we didn’t evolve from chimps, so they are useful as referential models rather than actual representatives of what our ancestors were like.” Chris Stringer of the Natural History Museum in London, who co-organized the meeting with Alan Walker of Pennsylvania State University, University Park, also sees a role for chimp work in evolutionary studies. “There is such a lot of excellent and important data on ape behavior,”  Stringer told Science, “that we would be foolish to throw it out as providing potential models for the behavior of early hominins.”

^*The First 4 Million Years of Human Evolution, London, 19-20 October 2009.

Photo credits (top to bottom): Cover; Jupiterimages

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

Reptiles look old school, and they have old school B cells that retain an ancient ability our B cells have lost, says a new study published today. Our B cells cannot engulf invading bacteria, but a turtle's can. The results help narrow down when the immune system's antibody factories stopped dining out.

The mammalian immune system divvies up the pathogen-fighting duties. Macrophages and similar cells perform phagocytosis, eating and destroying bacteria and other invaders. Instead of tangling with pathogens, B cells counterattack by pumping out antibodies that home in on intruders. According to immunologists, mammalian B cells aren't capable of phagocytosis.

Researchers infer that phagocytosis came first—single-celled organisms such as amoebas use the maneuver to capture food—and that B cells evolved from phagocytic cells (see the Origins essay on the evolution of the immune system). A 2006 study bolstered that hypothesis, showing that cells from fish and frogs have both abilities.

The question is when in vertebrate evolution some B cells lost their appetite for pathogens. Nobody had run a taste test on reptile cells, so a team from Illinois State University in Normal offered fluorescent beads to B cells from red-eared sliders, a kind of turtle (above). Some of the cells snarfed up the beads, indicating that they were capable of phagocytosis, report Laura Zimmerman and colleagues in Biology Letters.

These dining habits suggest that the B cells of mammals didn’t give up phagocytosis until after the group parted from reptiles. The researchers propose that B cells' double duty reinforces immunity in reptiles, whose antibodies aren't as potent or produced as quickly as those of mammals. To sharpen their picture of B cell evolution, researchers now need to determine whether bird B cells also abstain from phagocytosis.

Photo credit: Trisha M. Sears