rising@zoo.toronto.edu (Jim Rising) (11/17/90)
Since I posted some definitions a while back, I've received some email questioning Darwin's equation of Sexual & Natural Selection. I thought that I remembered a specific quote in his 1871 work, but confess that I don't find it--so I withdraw that statement. Doug Hemken sent me an interesting note that I'm certain he would not mind my posting, so here it is: Subject: Re: Sexual & Natural Selection To: rising@zoo.utoronto.ca X-Original-To: rising@zoo.utoronto.ca, doug.hemken@bbs.acs.unc.edu, HEMKEN It's tough going to Darwin for definitions. Many of the terms Darwin coined and used have not only long since been subtly reinterpreted, but also the theoretical framework in which they originally made sense has changed. For instance, Darwin's "pangenesis" model of inheritance has no place in contemporary thought. And the term 'natural selection' now has a broader meaning than I think Darwin himself gave to it. Darwin thought of natural selection and sexual selection as two distinct phenomena. "Sexual Selection acts in a less rigorous manner than Natural Selection. The latter produces its effects by the life or death at all ages of the more or less successful individuals" ([1877]:[226]). In other words, Darwin's 'natural selection' is equivalent to survivability. Darwin understood that both survival and finding a suitable mate produced more offspring, but he viewed these as two distinct selection mechanisms, and hence as two distinct mechanisms of evolution. In contrast, today we think of sexual selection as just one more type of natural selection. Where Rising quotes Darwin as saying that in most cases "it is scarcely possible to distinguish between the effects of natural and sexual selection" ([1877]:[210]), Darwin was actually trying to make the point that the phenotypic characteristics ('phenotype' being a post-Darwin concept) resulting from these two selection mechanisms are hard to sort out. I.e., given a characteristic distinguishing the male and the female of a species, it may be difficult to determine whether that characteristic is the result of natural or sexual selection. Darwin was not claiming that natural and sexual selection are nearly indistinguishable *as selection mechanisms*, but that their *results* might often be nearly indistinguishable. Because we today are the intellectual heirs of both the Mendelian model of inheritance and the Evolutionary synthesis, it is difficult to read Darwin casually without finding meanings Darwin probably did not intend. (First there were the Darwinians, then the Mendelians proved the Darwinians wrong! and then the Synthesis proved them both compatible. What a convoluted intellectual history!) That doesn't mean we shouldn't read Darwin, or that we can't still learn from him. But it does make him of limited use as a *contemporary* authority. Darwin used the term sexual selection in his 1859 _Origin of Species_, but he felt that the effect of sexual selection *on speciation* was insignificant, and that natural selection played the major explanatory role in 'the species question.' In _Descent of Man, and Selection in Relation to Sex_ (originally two separate books), Darwin attributes the term 'secondary sexual characters' to someone named Hunter, someone apparently well enough known no to require a footnote. ---------------------------------------------------------------- Darwin, Charles [1877] 1989 _The Descent of Man, and Selection in Relation to Sex_ (second edition), vols. 21 & 22 of _The Works of Charles Darwin_, Paul H. Barrett and R.B. Freeman, editors, London: William Pickering -- Name: Jim Rising Mail: Dept. Zoology, Univ. Toronto, Toronto, Ontario, Canada M5S 1A1 UUCP: uunet!attcan!utzoo!rising BITNET: rising@zoo.utoronto.ca