Thursday, July 12, 2012

What We're Reading: New Science Books

Lone Survivors: How We Came To be the Only Humans on Earth, by Chris Stringer

A few weeks ago we reviewed in this blog another book recently published on the search for the origins of our species, Ian Tattersall’s Masters of the Planet: The Search for Our Human Origins. Tattersall’s account was written for a popular audience, summarized the most recent developments in the field, and outlined areas of majority consensus on controversial and long-disputed issues among those intimately involved in the search for human origins. Tattersall summarized general ideas and trends without very detailed reference to research or the views of particular paleoanthropologists. By contrast, Chris Stringer’s book will appeal to those who, after reading Tattersall’s book, might be left with a desire to know more and understand the foundation of many of the ideas and conclusions expressed in a comparatively cursory fashion in that book. Stringer presents a much more detailed and thorough overview of most of the same material, one that is ultimately more satisfying, and, although it is a bit more difficult than Tattersall’s account, is nevertheless quite accessible to the general reader thanks to Stringer’s lucid expository style. What also makes Stringer’s account especially engaging is the story he tells us of his evolving views as a scientist studying in this field. He relates those to the major shifts in understanding that have occurred as a result of new research and discoveries since the middle of the last century. His personal engagement, thinking, and revisions in understanding, his journey as a major figure in the field, give his present conclusions an authority that we might not as readily accord to those of more distanced observers.

In the 1980s and 1990s Stringer was an important figure in the major shift that occurred in the modern history of paleoanthropology, the replacement of the multiregional model of the origin of our species, Homo sapiens. That model argued that Homo sapiens emerged regionally around the globe as an evolutionary development from more "primitive" species of humans, either Homo erectus or Homo heidelbergensis. Variations in species interbreeding were thought to have given rise to different racial origins. In the 1980s and 1990s, developments in molecular anthropology and more rigorous morphometric studies of old and newly discovered fossils became the foundation for the African Genesis or ROA (Recently Out of Africa) model of the development of Homo sapiens, the model that largely prevails in the field today. Recent discoveries in Africa, particularly early archeological sites that seem to suggest nascent modern cultural and cognitive developments of pre-Homo sapiens on the continent, reconsideration of early human fossil evidence from Africa, and discoveries of some "ancient" DNA in the human genome, have caused Stringer to somewhat modify his views.

Stringer now believes that Homo sapiens, modern man, was actually a development of a sort of multiregionalism on the African continent itself that occurred before Homo sapiens left Africa and eventually replaced older human species throughout the world. Stringer writes,
"Modernity was not a package that had a unique African origin in one time, place, and population, but was a composite whose elements appeared at different times and places and were then gradually assembled to assume the form we recognize today."
It should be noted that this is a more gradualist picture of human evolution than the model that Ian Tattersall champions, one that posits a "punctuated" view of evolution when it comes to Homo sapiens, the view of archaeologist Richard Klein who believes that there were episodic mutations in Africa in early modern humans that enhanced brain functions and produced significant changes in cognition and language. Tattersall believes that these behavioral changes followed a similar mutational event which had produced the distinctive Homo sapiens morphological and skeletal changes. So while Tattersal and Stringer basically seem to agree on the broad outlines of human evolution prior to the emergence of Homo sapiens, their views on the evolutionary events and processes surrounding the emergence of species differ significantly and serve to illuminate what are perhaps the major contending issues in the understanding of human origins that exist at this time, issues that compose a framework that will either accommodate future discoveries or will be elaborated and amended as this fascinating story continues to unfold. Besides being an excellent overview of the subject, Stringer’s book provides the reader with an understanding of how scientific inquiry works, tracing the dead ends, the visions and revisions involved in of how we come to know what we know.

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