Appendix 1
165
Muller’s Ratchet
Muller, H.J. 1964. The relation of recombination to mutational advance. Mutation Research 1:2-9. “There comes a level of advantage, however, that is too small to be effectively seized upon by selection, its voice being lost in the noise, so to speak. This level would necessarily differ greatly under different circumstances (genetic, ecological, etc.), but this is a subject which has as yet been subjected to little analysis … although deserving of it.” Muller anticipated the problem of near-neutral mutations, but failed to see the profound problems they create for evolutionary theory. He did realize that many diverse circumstances (not just population size) would amplify this problem. “It might appear as though a species without recombination would be … subject to genetic degeneration… This might be thought to be the case … However, this conclusion, which was misleadingly stated by the present author in a recent abstract, is only valid for the artificial conceptualization…nevertheless …an asexual population incorporates a kind of ratchet mechanism, such that … lines become more heavily loaded with mutation.” How extremely reticent Muller was, to acknowledge the very problem which soon came to bear his name! Throughout his career, Muller had a deep concern for radiation-induced mutation and human genetic degeneration, and was a leading advocate of eugenics. However, even as he wanted to warn the public of the problem of genetic deterioration, he appeared to be extremely careful not to make any statements which might detract from the “certainty” of evolutionary theory (apparently this reflected where he placed his highest loyalty). His statements above, about the problem of genetic degeneration within asexual species (for which he became famous - Muller’s ratchet), are so cautiously worded, that one can hardly discern his message. Muller argued that his “ratchet” was of only limited relevance - because he thought mutations were extremely rare. Therefore, he thought each mutation could be dealt with as a discrete and distinctly-selectable