In his book Wonderful Life (1989), Stephen Jay Gould argued that evolutionary history exhibits contingency: If you could rewind the tape of life and play it back again, you would observe different evolutionary outcomes each time. Simon Conway Morris, a paleontologist whose work on marine invertebrates of the Cambrian period inspired Gould, defends a view of evolution that is just the opposite of Gould’s. In Life’s Solution: Inevitable Humans in a Lonely Universe(2003), Conway Morris argued that convergence, rather than contingency, is the hallmark of evolutionary history. Evolutionary convergence is the development of a particular trait in independent lineages: for example, the evolution of wings (in bats, birds, insects, and pterosaurs) and the camera eye (in mollusks and vertebrates). Most biologists think that convergence occurs when natural selection adapts different lineages to similar environmental conditions. The real question is whether convergence is more than incidental. Might it be “a straw in the wind, pointing to a deeper pattern of biological organization” (p ix)? Does convergence suggest a deeper purposiveness in evolution? This debate about the relative significance of contingency versus convergence represents a new development in evolutionary science as well as in the discussion of the relation between science and religion.
This volume offers twelve contributions of mixed quality by scientists, philosophers, and theologians, including one paper by Conway Morris. Especially noteworthy is the paper by Richard Lenski, whose research team at Michigan State University has done experiments that replay the tape of evolution using populations of E coli bacteria in the lab. Following Lenski’s piece, paleontologist and theoretical morphologist George McGhee offers some intriguing speculations about the possibility of developing a “periodic table of life”. McGhee’s paper comes closest to making good on the promise of the title of this book, which is that evolutionary convergence has something to do with the “deep structure” of biology.
The middle part of the book consists of a cluster of scientific papers that explore the evolution of intelligence in plants, social insects, primates, and crows. There is also a fascinating paper by Hal Whitehead on convergent social structures in elephants and sperm whales. These papers illustrate the tricky problem of defining “intelligence”. The idea of plant intelligence seems baffling, until plant biologist Anthony Trewavas reveals that ‘intelligence’ is to be defined in very broad terms, as “adaptively variable behavior”. Don’t all living things exhibit adaptively variable behavior? This points toward a general problem that philosopher of biology Kim Sterelny (2005) identified in a review of Conway Morris’s earlier book: Whether the same trait evolves in two different lineages depends on how broadly or how narrowly you define the trait. If you define “intelligence” broadly enough, that virtually guarantees that intelligence will occur in many lineages.
The last third of the book shifts to talk of purpose in nature. Does evolutionary history have any aim or destination? Michael Ruse provides the clearest and most helpful discussion of purpose in Darwinian science. The functional role of adaptations naturally leads us to see purpose in evolution, but, Ruse and others warn, we must be careful not to conflate adaptational purpose with the idea that evolutionary history has an overarching purpose. The book then takes an abrupt theological turn with essays by Celia Dean-Drummond and John Haught. These authors do not engage much with the scientific details. Instead, they argue that a convergentist evolutionary biology can easily be combined with certain theological views, a claim that most scientists and philosophers would see as unproblematic. Perhaps a more interesting question is whether a convergentist evolutionary biology would lend support to those theological views. None of the contributors to this volume go quite so far as to defend an affirmative answer this last question.
In both his introduction and his contributed paper, Conway Morris himself seems a little reluctant to lay his cards on the table and say what exactly he thinks about the connection between evolutionary convergence and larger metaphysical and theological questions. In other contexts, however, he has been more forthright. In 2005, he delivered the annual Boyle Lecture at Cambridge University, entitled, “Darwin’s compass: How evolution discovers the song of creation” (published as Conway Morris 2006). The lecture provides a stronger taste of his thoughts on science and religion than he offers here. There he writes of a desperate need “to re-examine how science and religion not only must co-exist ... but far more importantly how science reveals unexpected depths to Creation while religion informs us of what on earth (literally) we are going to do about it” (2005: 3). He rejects Stephen Jay Gould’s “reckless canard of science and religion defining independent magisteria of influence” (2005: 3). That, in turn, suggests that he does think that evolutionary convergence has some theological significance. It’s just not entirely clear what the significance is supposed to be.
Gould, it seems, is the real nemesis here. Although the contributors to this volume represent a diversity of perspectives, no one speaks up for Gould’s claim that history is contingent. As many of the selections point out, contingency is the antithesis of convergence. It would have enriched the debate to include some discussion of why Gould thought that the case for contingency is so strong.
And why not expand the discussion of convergence beyond evolutionary biology? What convergence might mean for cultural evolution and the history of science would make for fascinating reading — think of Darwin’s and Wallace’s “convergent” discoveries of natural selection.
Overall, the science makes the book worthwhile. When the book moves beyond the empirical study of evolutionary convergence, things get a little murkier. The papers on crows and ants, elephants and plants, do leave one with the sense that convergence is an important phenomenon. This book provides an accessible, if one-sided, introduction to the discussion of contingency and convergence in evolution.