Great Chain of Beings

It doesn't take a brilliant mind to discern that there are extensive and orderly relationships among the creatures on this Earth. But it has taken a number of brilliant minds to try to explain why that is. Charles Darwin and Alfred Wallace were the first to articulate clearly the basics of what is still the prevailing view, that natural selection is responsible for the diversity and connectedness of life as we know it, giving a new kind of meaning to the order of life classically developed by Aristotle. We use these thinkers as representative of many others, whose work also contributed to our evolving modern understanding. However, their explanation didn't satisfy everyone—many naturalists thought it was incomplete and it challenged the fundamental world-view (not to mention long-held pronouncements) of many others. Beginning almost immediately after the publication of the first edition of Origin of Species, there has been a steady stream of resistance to the idea of natural selection, and many of the same arguments are still raised by skeptics nearly 150 years later. There are still religious and political agendas that lead to some opposition, but some unease continues within professional biology as well, and the basic problem has not really been resolved.

To biologists satisfied with the classical darwinian explanations, a blanket invocation of evolution by a persistent, consistent directive force of selection seems to suffice, though the long geologic time scale means this must generally be surmised rather than observed directly. To those who are not satisfied with so generic an assumption, the major problem is to understand more specifically how a simple process like blind (not teleological) natural selection could bring the diversity and apparent high degree of specificity of complex adaptations about, especially in terms of the genetic mechanisms that are responsible.

Here, we will try to present an integrated summary and overview of the major points of this book, much of which deals with this basic question. A modest number of basically simple general principles show how evolutionary processes can indeed have achieved what we see. Some of the generalizations are the classics that go back to Darwin and before. Others are not usually thought of as general evolutionary principles, although we believe they deserve that status and have tremendous

Genetics and the Logic of Evolution, by Kenneth M. Weiss and Anne V. Buchanan. ISBN 0-471-23805-8 Copyright © 2004 John Wiley & Sons, Inc.

Figure 17-1. (A) Aristotle; (B) young Darwin; (C) young Wallace. (A) Statue in Vienna art museum, copied from (Bowder 1982), (B) 1840 painting by George Richmond.

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