Saturday, May 05, 2012

Lone Survivors: How We Came To Be The Only Humans On Earth
By Chris Stringer
Times Books

There’s an illustration I recall from an old schoolbook that still defines the popular conception of human evolution (at least for those who believe in it at all.) It depicted a progression of primates, hairy apes becoming slightly less hairy and more two-legged until the crouching Neanderthals become the modern human, upright and standing tall, poised to invent subprime mortgages. It’s a tale of destiny and inevitable progress, and it’s pretty much wrong.

Chris Stringer is a prominent paleoanthropologist affiliated with the Natural History Museum in London. In this book he attempts a comprehensive survey of the still-changing picture of human species development. He begins with the state of knowledge in the 1970s, when he started his professional work, and he describes in some detail the factors involved in how that picture has changed. He explores fast-moving advances in contributing fields: not only in new techniques for locating and unearthing fossils, but in dating them with exotic new technologies (like the synchrotron, of which a very big example is the Large Hadron Collider.)

  Genetics now contributes in various ways, advancing with stunning speed. The human genome was essentially sequenced just 20 years ago. Now there’s a sequenced Neanderthal genome. Stringer also considers cultural questions based on artifacts such as tools, paints and musical instruments.   I found a lot of this interesting but also frustrating.  Paul Shepard shows--and evidence from contemporary Indigenous peoples as well as their traditions demonstrate--that humans learned a lot by imitating nature and other animals, as well as through their interactions with animals (in the hunt, for example, which Shepard suggests influenced the intelligence of both hunter and prey.)  Some cultural aspects Stringer finds mysterious may become less so if these factors are fully considered. 

Stringer writes a lot about how information was developed, so the big picture emerges in fragments. While all the new data answers some questions, basically it seems to have complicated the story. It’s now considered likely that several of many human species (an earlier book counted 22) coexisted in the same time, maybe in the same place. Modern humans carry some Neanderthal DNA (and before the caveman jokes start, Neanderthals males and females may have been more equal physically and culturally than are modern humans.)

New early humans have been discovered, notably a species called homo floresiensis discovered in 2004. Because of its small size, it was quickly dubbed “the Hobbit.” This species seems to have existed only on a single island near Java, and remains mysterious and very provocative in what it suggests about the vagaries of evolution. These humans existed—and died off--apparently in isolation perhaps just 18,000 years ago.  This suggests the fragility of a species' survival.  But then, for one reason or another, our own existence outside the Africa whence we came may be owed to only a few hundred surviving travelers.

    So how did we become the only humans on earth? Did modern humans develop traits that gave it competitive advantage through natural selection? In some ways that's likely, but traits that survived for no discernable reason (genetic drift) also helped. I’ve noticed that in recent years, historians are taking role of climate more seriously as a causal factor in the rise and fall of civilizations. Similarly, this book describes climate changes as crucial elements in the prehistoric story of human species. It may well be that one reason our species survived is that while other human species battled with extreme and disastrous effects of climate change, our forebearers were in southern Africa, with relatively stable climate.  Ironic perhaps in that this area is now being hit hard by today's climate crisis.

There are still plenty of puzzles, but Stringer concludes that we’re here at least partly by accident, by luck. “Sometimes the difference between success and failure in evolution is a narrow one,” he concludes, and notes that we’ve now got “an overpopulated planet and the prospect of global climate change on a scale that humans have never faced before. Let’s hope our species is up to the challenge.”

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