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Human evolution in search of an explanation. (Book Review).

The Riddled Chain: Chance. Coincidence, and Chaos in Human Evolution, Jeffrey K. McKee. x + 280 pp. Brunswick: Rutgers University Press, 2000. $27.00.

About 5 million years ago a divergence in primate evolution gave rise to the great ape lineage on the one hand and hominids including modern humans on the other. The fossilized common ancestor to these two lineages has yet to be found. We know that by at least 4 million years ago animals in the hominid lineage had taken to walking upright. At about 2.5 million years ago the hominid lineage diverged to produce robust, thick-jawed vegetable-eating animals and a line of more gracile hominids which included meat in their diet and made stone tools. The meat-eating toolmakers ultimately gave rise to extant tofu-eating internet users; whereas, the robust vegetarians became extinct.

Why, asks McKee, did early hominids become bipedal in the first place? And why did our gracile ancestors survive while the robust branch of the hominid line disappeared? Mckee's answer to these "why" questions is that there is no answer at all. He discards the view that natural selection triggered by climatic changes is an adequate explanation for human evolution. Instead, he maintains that the major events in human evolution were triggered by chance, coincidence and chaos.

If chance and other vagaries resulted in bipedalism, then our large brains, manual dexterity, and ability for spoken language are still in need of an explanation. In fact, McKee writes, " there really more to human evolution than our theories have captured so far? Despite our faults, humans are in need of an explanation... The explanation is autocatalysis (my italics)."

Descriptions, explanations, and examples of what is meant by chance, chaos, coincidence, and autocatalysis in human evolution occupy the major part of the book, and these all deserve comment and some criticism. But first it seems right to state that this is not just a book about human evolution. It is also a highly personal account of the scientific process. McKee is a practiced physical anthropologist/theoretical evolutionary biologist now at The Ohio State University who states at the outset that he believes science is fun. He communicates this enthusiastically and contagiously on virtually every page using down-to-earth language and engaging stories. His personal accounts of what life is like for a field anthropologist camping out in South Africa make science fun for the reader as well.

That science is not a collection of observations or "facts" but rather a non-dogmatic, If-correcting process by which we endeavor to understand the world and our place in it is also communicated very well in this book. The story of human evolution as a scientific discipline is littered with discarded and disproven hypotheses. McKee describes several of these and how each was an exciting and promising explanation for the data on hand at the time of its formulation. How new data produces new hypotheses and ultimately theories is clearly shown by McKee's examples. The relevance of these anthropological examples to other domains of science should be easy to recognize by most readers. Thus, non-scientists who often become frustrated with the apparent qualified or tentative nature of 'scientific facts" eggs are bad for you, no they are good; alcohol is bad for you, except in red wine; breast self-examinations save lives, no they don't; supplementary vitamin C prevents cancer, no sorry it causes it - should gain som e tolerance and understanding for the changing views of science by reading this book.

Now, back to chance, coincidence and chaos, "three ubiquitous and mischievous forces" claimed by McKee to be major players in producing all life forms on Earth. Three to 7 pages in Chapter 1 are devoted to describing each "force."

Chance is what makes the existence of every living individual highly unlikely. McKee tells us that the chance of his mother and father being horn female and male and of himself being born the last of four sons had less than a 1.6% probability. Multiply this by the likelihood that a particular egg and sperm would have united to produce the zygote that became Dr. McKee and you begin to get his drift.

Coincidence acquires an ambiguous meaning in McKee's hands. At first it appears to come in two varieties, that due to common cause and that not explicable by a common cause: "Coincidence, be it by cause or caprice, is part of all lives" (p. 9). But later on the same page, in a discussion of cause and effect in evolution, it is stated that "discerning the difference between mere coincidence and important causation is not only difficult but is severely hampered by the fragmentary nature of the fossil record." For example, McKee shows in Chapter 4 that peaks of first appearance of certain mammals in the fossil record need not have been caused by coincident changes in climate, but could be due simply to chances of fossilization and discovery. Although coincidence is never defined in the book, I will call it the occurring of nvo or more events at virtually the same time or place when no apparent cause for such occurrence can be discerned. This is consistent with dictionary definitions, and also I believe it is fa ir to the author's most frequent use of the term.

Chaos is defined. It "represents unpredictability based on sensitivity to initial conditions" (p. 13). Examples cited include versions of the famous "butterfly effect" (p. 14) whereby the beating of a butterfly's wings in Florence, Italy, may result in a hurricane making landfall in New Orleans six weeks later. The extreme sensitivity of chaotic systems to initial conditions makes them unpredictable and thereby results in the appearance of chance. Not only weather, but also evolution, is subject to chaos theory according to McKee: "Chaos develops when the various forces of evolution combine" (p. 16). This makes it impossible for our limited analyses of past climates, geographies, ecosystem compositions, hominid morphologies, etc. to yield an airtight, causative explanation for human evolution.

The first seven chapters of the book are devoted to explaining how chance, coincidence and chaos may have been more important in human evolution than the forces of environmental change acting through natural selection. This prepares us for Chapter 8 which presents the centerpiece of the book, autocatalysis.

"...autocatalytic evolution is a concept so simple, so basic, that it is actually difficult to explain, writes McKee (p. 204). But earlier it is described quite clearly: "Autocatalytic evolution simply means this: evolution is caused (catalyzed) by itself (auto). It is self-propelled by feedback loops' (p. 202).

Autocatalysis in human evolution refers to the interplay between bipedalism, brain elaboration, manual dexterity, dietary niche, language and material culture - each of these reinforcing the others through positive natural selection. It is suggested that the chance occurrence of bipedalism among our forest-dwelling primate ancestors along with the coincidental by-product of free hands (p. 205) set all of this into motion. (Note that this use of the word "coincidental" includes causation and therefore does not jibe with earlier descriptions of the term.) Later the adaptability allowed by an expanded neocortex in our larger brained, gracile hominid ancestors proved more successful than the adaptation of a massive skull and jaw for chewing vegetables acquired by the robust lineage of hominids.

These ideas are not new. McKee acknowledges that even Charles Darwin and Thomas Huxley had thought of the positive reinforcement that bipedalism, brain size, and tool use might have on each other. Edward O. Wilson discusses autocatalysis extensively in his book Sociobiology (Belknap Press of Harvard University Press. Cambridge, MA, 1977), although the term is absent from the glossary and index of the 2nd edition of Mark Ridley's widely used text, Evolution (Blackwell Science, Inc., Cambridge, MA).

McKee claims that autocatalytic evolution "holds a lot of explanatory power lacking from the neo-Darwinian synthesis of evolutionary theory (p. 202).. .and that the theory behind it should be more thoroughly investigated, for a lot of mammalian evolution, perhaps most of evolution, may be a product of autocatalysis" (p. 203). No examples of possible autocatalysis playing a role in the evolution of non-human organisms are given, although this is forgivable since the book is about human evolution. One would hope that data or a book would be forthcoming though to back up the suggestion of such great importance for autocatalysis in all of evolution.

The emphasis on the three "c" words seems a bit concocted to me. From what is written, chance is only an illusion created by chaos, and the unpredictability of chaos is simply due to our incomplete knowledge about initial conditions. From this doesn't it follow that nothing is really coincidental at all, at least in the sense of lacking causal connections to everything else? Although I suspect that the book is less ground-breaking than some of its passages imply, it is a "good read" for biologists and non-biologists alike, Non-scientists will gain an appreciation for the process of science, and every reader will have her imagination and interest tweaked by the discussions of how we came to be human.
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Title Annotation:'The Riddled Chain: Chance. Coincidence, and Chaos in Human Evolution'
Author:Bradley, James T.
Publication:Journal of the Alabama Academy of Science
Article Type:Book Review
Date:Oct 1, 2001
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