The Extended Phenotype: The Long Reach of the Gene (Popular Science) Read Free

better for it. The extended phenotype may not constitute a testable hypothesis in itself, but it so far changes the way we see animals and plants that it may cause us to think of testable hypotheses that we would otherwise never have dreamed of.
    Lorenz’s (1937) discovery that a behaviour pattern can be treated like an anatomical organ was not a discovery in the ordinary sense. No experimental results were adduced in its support. It was simply a new way of seeing facts that were already commonplace, yet it dominates modern ethology (Tinbergen 1963), and it seems to us today so obvious that it is hard to understand that it ever needed ‘discovering’. Similarly, D’Arcy Thompson’s (1917) celebrated chapter ‘On the theory of transformations …’ is widely regarded as a work of importance although it does not advance or test a hypothesis. In a sense it is obviously necessarily true that any animal form can be turned into a related form by a mathematical transformation, although it is not obvious that the transformation will be a simple one. In actually doing it for a number of specific examples, D’Arcy Thompson invited a ‘so what?’ reaction from anyone fastidious enough to insist that science proceeds only by the falsifying of specific hypotheses. If we read D’Arcy Thompson’s chapter and then ask ourselves what we now know that we did not know before, the answer may well be not much. But our imagination is fired. We go back and look at animals in a new way; and we think about theoretical problems, in this case those of embryology and phylogeny and their interrelations, in a new way. I am, of course, not so presumptuous as to compare the present modest work with the masterpiece of a great biologist. I use the example simply to demonstrate that it is
possible
for a theoretical book to be worth reading even if it does not advance testable hypotheses but seeks, instead, to change the way we see.
    Another great biologist once recommended that to understand the actual we must contemplate the possible: ‘No practical biologist interested in sexual reproduction would be led to work out the detailed consequences experienced by organisms having three or more sexes; yet what else should he do if he wishes to understand why the sexes are, in fact, always two?’ (Fisher 1930a, p. ix). Williams (1975), Maynard Smith (1978a) and others have taught us that one of the commonest, most universal features of life on Earth, sexuality itself, should not be accepted without question. Indeed, itsexistence turns out to be positively surprising when set against the imagined possibility of asexual reproduction. To imagine asexual reproduction as a hypothetical possibility is not difficult, since we know it is a reality in some animals and plants. But are there other cases where our imagination receives no such prompting? Are there important facts about life that we hardly notice simply because we lack the imagination to visualise alternatives which, like Fisher’s three sexes, might have existed in some possible world? I shall try to show that the answer is yes.
    Playing with an imaginary world, in order to increase our understanding of the actual world, is the technique of ‘thought experiment’. It is much used by philosophers. For instance in a collection of essays on
The Philosophy of Mind
(ed. Glover 1976), various authors imagine surgical operations in which one person’s brain is transplanted into another person’s body, and they use the thought experiment to clarify the meaning of ‘personal identity’. At times philosophers’ thought experiments are purely imaginary and wildly improbable, but this doesn’t matter given the purpose for which they are made. At other times they are informed, to a greater or lesser extent, by facts from the real world, for instance the facts of split-brain experiments.
    Consider another thought experiment, this time from evolutionary biology. When I was an undergraduate obliged to write