Friday, January 16, 2009

Archeogenetics - Our Past Within Us

The cross-disciplinary trend in the sciences is very cool. The more we see that things are interconnected, the better we will understand our world and our place in it. The new field of archeogenetics brings us one step closer.

Our Past Within Us

The new field known as archeogenetics is illuminating prehistory.

By Mark Williams

Prehistory: The Making of the Human Mind
By Colin Renfrew
Modern Library, 2008, $23.00

How did we become the thinking animals that we are? That's the question at the heart of the study of human prehistory--and the one that Colin Renfrew has been asking since the summer of 1962, when he travelled to Milos, one of the Cycladic Islands in the Aegean Sea, a source of the black obsidian that was the earliest commodity traded by humans.

Renfrew--Lord Renfrew of ­Kaimsthorn since he was made a British life peer in 1991 to honor his many contributions to archaeology--was then a graduate student at Cambridge. As an undergradu­ate, he'd first studied natural sciences before moving on to archaeology; thus, seeking a means to determine the provenance of the obsidian that prehistoric ­peoples favored for toolmaking, he tried the novel tactic of using optical emission spectroscopy to analyze its trace elements.

"We really hit lucky," Renfrew told me recently. "Obsidian makes much thinner, sharper blades than flint and so was a preferred substance found at almost all the early Neolithic sites in Greece. In fact, we learned it was already traded during the Upper Paleolithic." Yet the principal quarries for obsidian in the Aegean were on Milos. "So the material documents the earliest known seafaring," Renfrew says. "We needed nevertheless to be sure where it was coming from. Trace-element analysis let us characterize each different obsidian source, since they're created by relatively recent volcanoes and tend to be consistently distinguishable." Renfrew found that he could clearly graph how far the material had traveled: obsidian from a site in Anatolia (modern Turkey), in one instance, had been transported approximately 500 miles to Palestine. Overall, the picture that emerged suggested a world where most people never traveled more than a few miles from where they were born, but a few went everywhere. "It's an interesting picture," Renfrew says. "It was the seafarers who traveled distances, getting around the Aegean Islands quite widely and clearly doing that before the origins of farming."

Next, Renfrew turned his attention to what had been a cherished assumption in archaeology: that prehistoric cultural innovation originated in the Near East and diffused to Europe. "Just in archaeological terms, I didn't think that argument was very good," he says. "In Bulgaria and Romania, I'd been struck by the early metallurgy at some sites. So when radiocarbon dating arrived--particularly when tree-ring calibration came through in the late 1960s--the penny dropped." The new technological methods proved that, indeed, certain artifacts in Central and Western Europe were older than their supposed Near Eastern forerunners. Renfrew wrote a book, Before Civilization: The ­Radiocarbon Revolution and Prehistoric Europe (1973), pointing out that "the previous diffusionist chronology collapsed at several points."

Over the decades, Renfrew has remained at his field's cutting edge; he was among the earliest advocates of technologies like computer modeling and positron emission tomography (PET), the latter to examine contemporary subjects' brain activities as they replicated the toolmaking of Lower Paleolithic hominids. In his latest book, Prehistory: The Making of the Human Mind, Renfrew has not only produced a summary of by far the vaster part of human history but also provided an account of archaeology's advance since European scholars realized some 150 years ago that the human past extended many millennia further back than 4004 b.c.e. (the 17th-century theologian Bishop Ussher's estimate of when God had created the world). Given its vast subject and its strictures of length, probably the only real criticism one can make of the book is that in its index, under the letter R, the author is missing. It's a significant omission: Renfrew has informed today's understanding of human prehistory much as he says Gordon Childe--who is responsible for the concepts of the Neolithic and urban revolutions--shaped thinking during the first half of the 20th century. Like Childe, he has been one of the great archaeological synthesizers, working to construct a theory of global human development. For Renfrew, all archaeology ultimately leads to cognitive archaeology--the branch that investigates the development of human cognition.

In particular, Renfrew has been preoccupied by what he has dubbed the "sapient paradox": the immense time lag between the emergence of anatomically modern human beings and the advent of the cultural be­haviors that we take to define humanity.

Prehistory is defined as that period of human history during which people either hadn't yet achieved literacy--our basic ­information storage technology--or left behind no written records. Thus, in Egypt, prehistory ended around 3000 b.c.e., in the Early Dynastic Period, when hieroglyph-inscribed monuments, clay tablets, and papyrus appeared; in Papua New Guinea, conversely, it ended as recently as the end of the last century. Archaeologists and anthropologists accept this region-by-region definition of prehistory's conclusion, but they agree less about its beginning. A few have seen prehistory as commencing as recently as around 40,000 b.c.e., with the emergence of Cro-Magnon man, who as Homo sapiens sapiens was almost indistinguishable from us (although Cro-Magnons, on average, had larger brains and more robust physiologies). However, most experts would probably say that prehistory began in the Middle Pleistocene, as many as 200,000 years ago--when Homo neanderthalensis (sometimes classified as Homo sapiens neanderthalensis) and archaic Homo sapiens emerged. Either way, it's assumed that the appearance of Homo sapiens sapiens triggered "a new pace of change ... that set cultural development upon [an] ... accelerating path of development," as Renfrew writes in Prehistory. But Renfrew thinks that this acceleration must have been due to something else.

"The evidence that Homo sapiens' arrival equates with full linguistic abilities, the human behavioral revolution, and so on is very limited," Renfrew told me, adding that he sees nothing clearly separating the flint tools of the Neanderthals from those associated with Homo sapiens. As for the cave paintings at Altamira, Lascaux, and other Southern European sites, which are 15,000 to 17,000 years old: "They're amazing, but stylistically singular and very restricted in their distribution. They mightn't be characteristic of early Homo sapiens." Overall, Renfrew thinks, if aliens from space had compared Homo sapiens hunter-gatherers with their earlier counterparts, they probably wouldn't have seen much difference.

Two and a half million years ago, the first protohumans, Homo habilis, shaped stones to take the place of the claws and fangs they lacked, using them to kill small animals and scavenge the remains of larger ones. The payoff was immense: whereas metabolic needs like food processing constrain brain size for most mammals, eating meat enabled habilis to start evolving a smaller gut, freeing that metabolic energy for the brain's use. After a few hundred thousand years, later hominids like erectus and ergaster had developed straightened finger bones, stronger thumbs, and longer legs. The expansion of hominid brains--they were twice as big within a million years, three times by the Middle Paleolithic--enabled symbolic communication and abstract thought. By 50,000 b.c.e., our ancestors had spread from Africa through Asia, Europe, and Australia.

Archaeogenetics Emerges
The paradox, or puzzle, is this: if archaic Homo sapiens emerged as long as 200,000 years ago, why did our species need so many millennia before its transition, 12,000 to 10,000 years ago, from the hunter-­gatherer nomadism that characterized all previous hominids to permanent, year-round settle­ment, which then allowed the elabo­ration of humankind's cultural efforts? To answer this question, Renfrew calls for a grand synthesis of three approaches: scientific archaeology, which collects hard data through radiocarbon dating and similar technologies; linguistic study aimed at constructing clear histories of the world's languages; and molecular genetic analysis.
Read the rest of this article.

No comments: