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November 2009 Archives

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.

OldEurope.18. Set of twenty one

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.

OldEurope.8. the_thinker_hi 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.

PHOTO CREDITS:

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

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 23, 2009

A Plethora of Hobbit Papers

by Elizabeth Culotta

Fans of Homo floresiensis will be happy this month, as the Journal of Human Evolution (JHE) has a special issue devoted to these diminutive hominins whose fossils were found on the Indonesian island of Flores. There’s also a new paper out in Significance, the Royal Statistical Society journal, in which William Jungers and Karen Baab add more analyses to back up the contention that the little people from Liang Bua cave are a new kind of hominin rather than diseased modern humans.

539px-Homo_floresiensis.fromwiki The JHE special issue covers every aspect of hobbit lore, including limbs, teeth, skull, geology, and stone tools. The papers have been posted online as they became available, and some of the work has been presented at meetings, so some findings have been in the news already. For example, at Science, we have recently covered the surprising similarity in stone tools from the H. floresiensis and H. sapiens levels, the hobbit’s unusual shoulder, and her primitive and strange feet. The special issue gathers an impressive amount of description and analysis in one place and includes a preface by co-discoverer Mike Morwood of the University of Wollongong and the University of New England, Armidale, and his colleagues.

Photo credit: Ryan Somma


by Virginia Morell

 penguin3

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

Tree_of_life_by_Haeckel 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 5, 2009

On the Origin of Religion

by Elizabeth Culotta

1106N_IntroArt 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 thendarwin 16-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.

213027001_16ec6219d5Stickleback 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.

blog_gall.ants 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 acrossblog_gall.tree 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