Origins

Long before humans painted caves or made colorful necklaces out of snail shells, they manufactured beautifully symmetrical, teardrop-shaped stone tools that archaeologists call hand axes, such as the ones shown at left from Atapuerca, Spain. At least, hand axes seem beautiful to us today, even if their exact function and meaning are a matter of debate. Most archaeologists think that hand axes, which begin showing up at archaeological sites about 1.7 million years ago, were used to cut plants and butcher animals. And many assume that making such a symmetrical object required a mental template and the ability to impose a predetermined form on a piece of stone. As I discuss in this month’s Origins essay in Science, these talents could be considered proxies for symbolic capacities. And some researchers—as I discuss in a Random Sample in this week’s issue of Science—have suggested that hand axes were also the result of Darwinian “sexual selection.” According to this controversial idea, a well-made hand ax was a sign that its maker, presumed to be a guy, had good genes and would be a suitable mate for any gal lucky enough to have him.

So hand axes have been considered to be handy tools, courting devices, and signs of symbolic smarts. But what if they were none of these things? Since the early 1990s, one archaeologist has argued that there is no evidence early humans actually intended to make hand axes. Iain Davidson, now a professor emeritus at the University of New England (UNE) in Armidale, Australia, contends that the hand ax might have been what was left over when toolmakers were done striking sharp flakes from a stone core.

Davidson first argued for what he calls the finished-artifact fallacy in 1993, together with UNE psychologist William Noble, and he has elaborated on the idea in more recent publications. I caught up with him late last year at Harvard University, where he is currently a visiting professor. Over a long and pleasant lunch in Harvard Square, he made it clear that he has not changed his mind on the issue.

For one thing, Davidson says, archaeologists tend to focus their studies on the most symmetrical hand axes, thus introducing a bias into their analyses. They see more patterning than really exists on average and then interpret that patterning as evidence that early humans intended to create tools that look that way. And because hand axes were probably made by striking flakes from a core with a second stone—indeed, the marks where the flakes were taken off are clearly visible on the hand ax—archaeologists are making unproven assumptions when they conclude that the hand ax rather than the flakes were the most important product, Davidson contends. At the 500,000-year-old site of Boxgrove in England, for example, where hundreds of hand axes have been found, there are also signs that the flakes taken from them were used as tools by early humans.

“I can imagine a situation at Boxgrove where [early humans] were walking around with a core, striking off flakes when they needed them, and then abandoning the core when it was no longer useful,” Davidson told me. As for why the core would have that characteristic teardrop shape, Davidson explained that it would be easier to hold in the hand if you only took flakes off of one end.

Davidson’s view is definitely a minority one. “The form of [hand axes] clearly reflects the intention of the toolmakers,” says archaeologist Dietrich Stout of University College London. But few archaeologists argue that the flakes could not also have been used as tools, and Davidson’s idea does appeal to some. Anthropologist April Nowell of the University of Victoria in Canada, who challenges the sexual-selection hypothesis, told me that she is “sympathetic” to Davidson’s notion. “People get hung up on the symmetrical form that some [hand axes] have,” Nowell said. “We have exaggerated what a typical hand ax looks like, and we don’t think about the less refined ones. There is a variation from tools that just look like cores to those that look like hand axes.”

—Michael Balter

About Iain Davidson

Excavations at Boxgrove

PHOTO CREDIT: José-Manuel Benito Álvarez

When the Chauvet Cave in southern France was discovered in 1994, it rocked the archaeological world, in part because its paintings of lions, horses, and rhinos were spectacularly sophisticated—and also because radiocarbon dating suggested that these artworks had been executed as early as 32,000 years ago, making them the oldest known cave paintings. (Because there is no agreed radiocarbon calibration curve for dates earlier than 26,000 years ago, all dates are given in uncalibrated "radiocarbon" years; actual calendar dates are probably several thousand years earlier. See Science, 15 September 2006, p. 1560.)

Yet while Chauvet's paintings are unparalleled for their age in skill and technique, they did not stand entirely alone in the prehistoric art world. Indeed, many prehistorians were not completely surprised at their discovery, because there were already numerous indications that modern humans in Europe were making art that early; since Chauvet's discovery, a number of subsequent finds have confirmed that conclusion.

Chauvet may shelter the earliest cave paintings (but see below), yet previous excavations in Europe had found sculptures at least as old. Beginning in the 1930s and continuing until quite recently, archaeologists working in the Swabian Jura region of Germany have uncovered more than 20 figurines skillfully carved from mammoth ivory, including a superb half-lion, half-man sculpture from Hohlenstein-Stadel (see photo at left). Once radiocarbon dating became available after the 1950s, researchers found that these figurines were between 30,000 and 36,000 years old. The most recent objects, including a carved bird and a horse, were found in Hohle Fels Cave and reported by Nicholas Conard of the University of Tübingen in 2003. They too are at least 30,000 years old.

Did Neandertals use symbols and create art? This is the subject of one of the biggest, longest, and most contentious debates in the history of archaeology. Today, most researchers would agree that there is not a simple "yes" or "no" answer. But they might not agree on much else—just one more reason why Neandertals, whose genome sequence was announced today, are so intriguing.

Clearly identifiable Neandertal bones (like the front skeleton at left) appear no later than 130,000 years ago, often together with relatively sophisticated stone tools. But for about 90,000 years after that, there is little evidence that Neandertals produced anything that might be called art. There is certainly no indication that they ever painted caves, such as the spectacularly decorated Chauvet and Lascaux caves in France or Altamira in Spain, although one never knows what discoveries the future might hold—and one maverick archaeologist, Robert Bednarik (whom we featured last week) argues that Chauvet might have been painted by Neandertals, a decidedly minority view.

On the other hand, some researchers have complained bitterly that many colleagues are too quick to use the apparent absence of evidence for Neandertal symbolism to deny them their full humanity. John Speth, an anthropologist at the University of Michigan, Ann Arbor, expressed this view in the ironic title he gave to a 2004 paper in the journal World Archaeology: "News flash: negative evidence convicts Neandertals of gross mental incompetence."

I want to be the rap version of Richard Dawkins.

—Baba Brinkman lyric

What’s a fan of evolution to do this week when confronted with so many events celebrating Darwin’s 200th birthday? On Monday, for example, one could have been in London for a debate, hosted by our friendly rival Nature, on whether humans are still evolving. What about a London reading of Darwin-related poems by one of his relatives? It would fit with the art theme of this month’s Origins essay, but it wasn’t quite compelling enough, especially when an even more provocative event was taking place here in Cambridge, where Darwin studied. Welcome to the “Devil in Dover and the Rap Guide to Evolution,” a traveling road show sponsored by the British Council and organized by microbiologist Mark Pallen, the author of The Rough Guide to Evolution (and its related blog).

The rain and sleet, and lack of publicity, meant that only a few dozen people filled the cavernous Cambridge University lecture hall. The opening act featured American journalist Lauri Lebo, who covered the 2005 trial in Dover, Pennsylvania, in which parents sued to prevent the school board from forcing the teaching of intelligent design in science classes. Lebo has written a book about the trial, The Devil in Dover, and she and plaintiff Cyndi Sneath discussed how the case ignited a civil war within the small town, with some of the parents even being called atheists by neighbors despite being regular churchgoers. Perhaps Lebo’s most powerful reminiscences concerned how she tried throughout the trial to convince her father, a religious fundamentalist, that the school board was acting dishonorably.

No one had started clapping rhythmically yet, but it was still time to bring on the headline act: Baba Brinkman, a former English literature student and Canadian hip-hop artist whose major claim to fame is his rap take on The Canterbury Tales—hence the boast on his MySpace page that he’s the Geoffrey Chaucer of hip-hop. Lebo herself was anxious to hear the so-called lit-hop artist, noting, “Anyone who can work Australopithecus afarensis into a rap impresses me.”

Science writer and author of Microcosm: E. coli and the New Science of Life Carl Zimmer wrote the "On the Origin of Life on Earth"  last month. Today he discusses evolution on other worlds.

Imagine you spent your whole life on a tiny island, with only some tortoises and snails to give you a clue to what life was like. You'd be forgiven for failing to imagine a Venus flytrap or an armadillo. Evolutionary biologists are in much the same bind. They are, for the time being, stuck on a planetary island, only able to study life on Earth. While life on Earth takes many forms, every living thing is nevertheless a variation on the common theme of DNA, RNA, and protein. What kind of life, if any—exists on other planetary islands we don't know?

If we do discover life someday on another planet, evolutionary biology would leap to a new level. Biologists would be able to compare how evolution played out on two separate planets. If life began independently on another world and ended up a lot like life on Earth, that might mean that evolution must follow certain rules no matter where on the universe it plays out. Or perhaps evolution has the potential to be a lot weirder than we know, because we're stuck here on our little island of life. The closest place where it makes sense to look for life is Mars. Its surface may have been warm and wet in the past, and puffs of methane discovered in recent years just might be a sign that microbes are still thriving deep under the surface. The best way to see if that's the case is to drill into the Martian soil and find them.

But Chris McKay of NASA warns in this week's Science that in our search for a second biosphere, we may contaminate it with our own. As McKay points out, space scientists were already concerned about contaminating other planets in the 1960s. NASA completely sterilized the Viking Probe that landed on Mars in 1976, but the results of that mission suggested that the Red Planet was so harsh that no life could survive and so fewer protections were necessary. The Mars rovers that we've all watched wandering across the Martian landscape probably brought hundreds of thousands of bacteria with them.

Yet, over the years, scientists have grown more concerned again. The surface of Mars is clearly an awful place for even the hardiest microbe. But if we start drilling down into the ground, we might well be injecting microbes from Earth down into a Martian ecosystem. We unfortunately know all too well what happens when we accidentally introduce species to new places. At worst, the new species becomes invasive and drives native animals and plants extinct. At best, native ecosytems are dramatically altered. Do we have an ethical obligation to protect what McKay called "indigenous biospheres"?

Later this year, a meeting will be held to consider just this question. We do need to take responsibility for our actions, but we also should not forget another lesson of evolution here on Earth: Invasive species don't always need people to deliver them to a new home. Darwin himself first recognized that seeds and eggs can been carried to distant islands on the feet of birds. In space, meteorites may act as interplanetary birds, bringing microbes from Earth to Mars—or perhaps the other way as well. Even if we take every possible precaution, the life we find on Mars may turn out to be invasive after all. It just invaded Mars a billion years ago.

—Carl Zimmer

The origin of art ignites strong passion among the people who study it. Michael Balter, who wrote an essay on the origin of art and symbolic behavior for this week’s issue of Science, offers additional insight into one controversial figure of the paleoart world.

How old is the oldest art? As discussed in my essay, many researchers have given up on chasing after ever-earlier objets d’art in the archaeological record, preferring instead to look for early signs of symbolic behavior—of which art is simply one manifestation.

But one archaeologist who has not given up is Australia-based independent researcher Robert Bednarik.

Credit: F. D'Errico and A. Nowell