Newsgroups: sci.bio
Path: utzoo!rising
From: rising@zoo.toronto.edu (Jim Rising)
Subject: Sexual & Natural Selection
Message-ID: <1990Nov7.162026.14977@zoo.toronto.edu>
Organization: U of Toronto Zoology
Date: Wed, 7 Nov 90 16:20:26 GMT

Darwin was, I believe, the first person to use the term "sexual
selection" in "The Descent of Man, and Selection in Relation to
Sex" (1871).  Darwin saw sexual selection as a part of natural
selection, and notes (p. 257) that "...in most cases it is scarcely 
possible to distinguish between the effects of natural and sexual
selection."  About sexual selection, he writes:
 "[Sexual selection]...depends on the advantage which certain 
individuals have over other individuals of the same sex and species,
in exclusive relation to reproduction (p. 256)", and further:
  "There are many ... structures and instincts which must have been
developed through sexual selection--such as the weapons of offence and
the means of defence possessed by the males for fighting with and 
driving away their rivals--their courage and pugnacity--their ornaments
of many kinds--their organs for producing vocal or instrumental music--
and their glands for emitting odours; most of these latter structures
serving only to allure or excite the female.  That these characters
are the result of sexual and not of ordinary selection is clear, as
unarmed, unornamanted, or unattractive males would succeed equally 
well in the battle for life and in leaving a numerous progeny, if 
better endowed males were not present. (p 257-8)"  

Of course, we are under no obligation to follow Darwin's definition,
but it is clear that he reserved the use of "sexual selection" to explain
the evolution of structures or characteristics that otherwise were 
irrelevant to fitness, and perhaps (usually?) actually decreased
survival fitness.  

I don't know what Gould says, but John Alcock in a recent text
(Animal Behavior, Sinauer Assoc., 1989) defines Sexual Selection as:
  "A form of natural selection that occurs when individuals vary 
  in their ability to compete with others for mates or to attract
  members of the opposite sex.  As with natural selection, when the
  variation among individuals is correlated with genetic differences,
  sexual selection leads to genetic changes in the population."

This seems consistent with Darwin's usage.
-- 
Name:     Jim Rising
Mail:     Dept. Zoology, Univ. Toronto, Toronto, Ontario, Canada    M5S 1A1
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