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December 28, 2009

The End of Origins

image This year, the worldwide community of science has marked the bicentennial of Charles Darwin’s birth—and the 150th anniversary of the publication of On the Origin of Species—with dozens of evolutionary-themed meetings, books, review papers, and Science’s own monthly Origins series. In this blog, we’ve both joined in and reported on these celebrations, covering the meetings, expanding on the essays, and highlighting the most current research on evolution in all its many forms. Now the blog, like the year itself, draws to a close; this will be our final entry. We hope you have found it both diverting and useful.

Of course, Science’s interest in origins and all things evolutionary continues. For although 2009’s evolutionary parties are ending, the science behind them continues to serve as the firm foundation of modern biology as well as a rich source of new research. You can see all our Year of Darwin coverage in one place here, and you can continue to find the latest on evolution in online news at ScienceNOW and in the news and research in the magazine itself. Thanks for reading!

The Origins Blog Editors: Elizabeth Culotta, Elizabeth Pennisi, John Travis

December 3, 2009

On the Origin of Tomorrow

by Elizabeth Pennisi

image More than ever before, the future is in our hands. We are shaping not just our own destiny but also the destinies of much of life on this planet. That is the take-home message of the final essay, On the Origin of Tomorrow, in Science's Origins series.

As Carl Zimmer points out in this essay, Charles Darwin gave a nod to the future, finishing On the Origin of Species with a paragraph that talked about continuity: "... endless forms most beautiful and most wonderful have been, and are being, evolved.” He recognized that as long as the ingredients for the evolutionary process still exist, life has the potential to change. He didn’t believe it was possible to forecast evolution’s course, but he did expect humans would have a big effect—they had demonstrated this power already by domesticating plants and animals and driving some species to extinction. Darwin also expected that our own species would change.

As the world celebrates the 150th anniversary of the publication of On the Origin of Species this year, scientists continue to think deeply about what lies ahead. Some feel a new sense of urgency about understanding what might happen. Since Darwin’s day, humans have gained an unprecedented influence over our own evolution. At the same time, our actions, be it causing climate change, modifying the genomes of other organisms, or introducing invasive species, are creating new sources of natural selection on the flora and fauna around us. “The decisions we and our children make are going to have much more influence over the shape of evolution in the foreseeable future than physical events,” says Andrew Knoll, a paleontologist at Harvard University.

In this essay, Zimmer examines Darwin's perspective on the future and discusses how humans have helped to alter the course of their own evolution. He describes the ways humans have shaped the world around them—through global change, for example—and thereby affected the futures of countless other organisms and ecosystems. Finally, he ends with the question of whether humans will ultimately be smart enough to prolong the life of the planet.

Image: Katharine Sutliff

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.”

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 Michael Balter

blog_newskull 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 Carl Zimmer

As I was working on my essay on the evolution of eukaryotes, I spoke a lot to Nick Lane. Lane is trained as a biochemist, but he's also a prolific author (most recently of the book Life Ascending). As a result, Lane is that particularly rare breed: a scientist who can not only offer a bird's-eye view of an entire field but also tell you about his own very interesting ideas. Now Lane has just won a prize to spend the next 3 years further exploring some of those ideas.

Lane is the first winner of the £150,000 Provost's Venture Research Prize, awarded by the University College London, where Lane has been an honorary reader since 2006. According to UCL, "the Provost's Venture Research Prize will go to UCL researchers whose ideas challenge the norm and have the potential to substantially change the way we think about an important subject."

Lane won the award for his proposal to tackle a few simple but profound questions:

Why have complex cells evolved only once in 4 billion years? Why do they share many unexpected traits like sex and senescence? If these traits offer a selective advantage, why do bacteria not take advantage? On current thinking, the answers to these questions should arise from genetics, but a narrowly genetic perspective suggests that complex life should evolve repeatedly.

Lane plans to flesh out a hypothesis I described in my essay: He suspects that a rare merging of two species made this complexity possible. Only after our single-celled ancestors engulfed bacteria (that are now mitochondria) did they get enough energy to build and run a complex cell.

"It will start out mostly theoretical," Lane wrote me in an e-mail. "I want to piece together a broad framework from the full breadth of the literature." Lane will then launch a series of experiments to test his idea—"through collaborations with labs who know what they're doing."

 by Elizabeth Pennisi


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

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

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

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

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

Image: Katharine Sutliff

September 3, 2009

On the Origin of Cooperation

90904N_IntroSketch 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

Taforalttout.nassarius Anatomically modern humans evolved in Africa nearly 200,000 years ago, but researchers have long debated why there seems to be a gap between when hominins started looking modern and when they began acting modern. Some of the most important indications of modernity, such as cave art and certain types of advanced tools, don’t show up in the archaeological record until about 40,000 years ago, mostly in Europe. That has led some scientists, notably archaeologist Richard Klein of Stanford University in Palo Alto, California, to argue that modern human cognition, including language and other complex symbolic behavior, needed the additional kick-start of a genetic mutation about 50,000 years ago.

Yet an increasing number of researchers have come to think that Homo sapiens was capable of modern behavior from the very beginning of its history. Whether those behaviors show up in the archaeological record, these researchers say, depends on a variety of factors unrelated to genetics, such as how big and widespread early human populations were and what environmental challenges they faced. A team led by archaeologist Francesco d’Errico of the University of Bordeaux in France will soon publish what it considers yet more evidence for this viewpoint online in the Proceedings of the National Academy of Sciences (PNAS). Although the paper is still unpublished, PNAS has released the embargo on it, which will be available here when published. D’Errico and colleagues describe 25 shell beads, including those shown above, claimed to have been used as personal ornaments and found in four sites in Morocco dated between 85,000 and 70,000 years ago.

If this sounds familiar, that’s probably because d’Errico and others have recently published numerous sightings and analyses of shell beads from sites in Morocco, Algeria, South Africa, and Israel as old as 100,000 years ago. Nearly all researchers, including Klein, agree that personal ornaments are solid indications of modern behavior. Wearing jewelry is a form of symbolic signaling of personal identity to other hominins. And the use of symbols, scientists also agree, is a hallmark of modern human behavior—even if there are indications that earlier hominins might also have ventured into this cognitive realm.

Yet Klein has questioned many of the claims made by d’Errico and others, arguing most recently in a 2008 review in Evolutionary Anthropology that the holes found in the shells, which presumably allowed them to be strung as beads, were the result of natural abrasion from the action of the sea. He also points out that there are very few such examples in Africa. Given the near total absence of shell beads in Africa between 70,000 and 40,000 years ago, Klein suggests that the relatively infrequent earlier sightings do not represent a real symbolic tradition that endured over time. The new PNAS paper cites Klein’s Evolutionary Anthropology critique and counters with a detailed analysis of the newly discovered shell beads from the four Moroccan sites: Taforalt, Rhafas, Ifri n’Ammar, and Contrebandiers, which are dated by various techniques, including optically stimulated luminescence, thermoluminescence, and Uranium-series isotopic measurements.

Nearly all of the shells, the team writes, are from the genus Nassarius, a sea snail that shows up in archaeological sites all over Africa, Asia, and Europe. Moreover, three of the four sites are located about 50 kilometers from a coast, reinforcing the suggestion that the shells were deliberately transported inland and used for symbolic purposes, the team says. The team also notes that fragments of gravel inside shells and signs of mechanical erosion from lying on the seabed suggest that many snails were dead before they were collected. Thus they weren’t transported inland to be eaten. Finally, at some sites, the team found signs of ochre pigment clinging to the outside of the shells, which many archaeologists consider evidence of symbolic behavior.

But if hominins could create personal ornaments as early as 100,000 years ago, why have researchers found so few of them between 70,000 and 40,000 years ago in Africa and the Near East? The team points out that after 70,000 years ago, the climate turned markedly colder in both the Northern and the Southern hemispheres. When the temperature was warmer, the team writes, modern human populations were growing and “marine shell beads may have been instrumental in creating and maintaining exchange networks between coastal and inland areas. …” In other words, ornaments were a means for hominin groups to communicate their identities to each other. But the arrival of harsher conditions, and the possible resulting population crashes, “may have disrupted these networks through the depopulation of some areas, thereby isolating hunter-gatherer populations to the extent that such social and exchange networks became untenable.”

The article is part of a PNAS Special Feature series on “Out of Africa,” edited by none other than Richard Klein himself, who told Science that the d’Errico et al. paper adds “balance” to the issue. Some papers are being published online ahead of time; the entire Special Feature is tentatively scheduled for publication in late September, according to the PNAS press office.

—Michael Balter

CREDIT: Copyright d'Errico/Vanhaeren

90807IntroArtToadstools, people, plants, and amoebae have strikingly similar cells. All these organisms keep their DNA coiled up in a nucleus. Their genes are interspersed with chunks of DNA that cells have to edit out to make proteins. Those proteins are shuttled through a maze of membranes before they can float out into the cell. And these cells all manufacture fuel in compartments called mitochondria.

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

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

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

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

—Elizabeth Pennisi

Image: Katharine Sutliff