Sex has long been a difficult problem for Darwinian theory. “The existence of sexual reproduction poses a big theoretical puzzle to Darwinians.” (Dawkins 1986, p. 268). Although in some species, such as our own, sex is necessary for reproduction, that is not its adaptive function. Many lower organisms reproduce asexually (cloning). In many of these species, organisms switch to sexual reproduction at some stage in their life cycle. There are species, such as dandelions, that have even reverted from sexual reproduction to asexual. If reproduction was the function of sex, cloning would be far simpler, more efficient and wouldn’t require males. Moreover, even in species in which reproduction is tied to sex, reproduction itself doesn’t explain the genetic manipulations that accompany sex, including the intricate molecular processes involved in meiosis and crossing-over. Furthermore, conjugation, which like sex involves genetic manipulations in the transfer of DNA, occurs separate from reproduction.
That sex is a puzzle should be embarrassing for evolutionary biology. Sex must be extremely important. Most organisms reproduce sexually at some point in their life cycle. Sexual reproduction is present in all taxa and most species. No known “higher” organisms have evolved through cloning. All either reproduce sexually (at least periodically) or evolved from ancestors that did. (Bell 1982, p. 437; Maynard Smith and Szathmary 1995, pp. 164-66). As research of microorganisms has progressed, it is no longer even clear that any lower organisms have evolved by cloning since they engage in conjugation.
Not only should it be embarrassing, that sex remains a puzzle should be a clue that something fundamental is wrong with the whole neo-Darwinian framework. A leading theorist on the subject, John Maynard Smith, once remarked that “[o]ne is left with feeling that some essential feature of the situation is being overlooked.” (Ridley 1993, pp. 40-41, quoting Smith). The essential feature that has been overlooked, which Maynard Smith did not consider, is that population genetics and the concept of chance mutation are wrong. After describing sex as inconsistent with evolutionary theory, Williams stated that his “purpose is to propose minimal modifications of the theory to account for the persistence of so seemingly a maladaptive character.” (Williams 1975, Preface, v). The argument that follows is that sex can’t be solved with minimal modifications to neo-Darwinism; neo-Darwinian theory needs radical surgery, including removal of the concepts at its core.
The hypothesis set forth in this book is that genetic rearrangements are not due to “mutations” in the sense of random errors. Rather, they are produced by experimental genetic tinkering. This is the adaptive function of sex in higher organisms. It is the adaptive function of conjugation in lower organisms.
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