Darwin’s Sexy Sons May Not Be Sexy Enough
He who admits the principle of sexual selection will be led to the remarkable conclusion that the nervous system not only regulates most of the existing functions of the body, but has indirectly influenced the progressive development of various bodily structures and of certain mental qualities. Courage, pugnacity, perseverance, strength and size of body, weapons of all kinds, musical organs, both vocal and instrumental, bright colours and ornamental appendages, have all been indirectly gained by the one sex or the other, through the exertion of choice, the influence of love and jealousy, and the appreciation of the beautiful in sound, colour or form; and these powers of the mind manifestly depend on the development of the brain.
And that is Darwin’s female aesthetic doing a lot of the work of driving evolution.
But we are still left with the problem of the sensible female. A female aesthetic that drove males to evolve deleterious traits beyond a certain point would be absurd, and in fact, evolutionary biologists have coined the term for when and if this happens “Runaway Sexual Selection.” If you are a reader of S.J. Gould you could not have missed the story of the Irish Elk, for instance. Female choice for larger and larger antlers drove the elk to have such large antlers that when climate changed a bit and the environment got more woody, they got all tangled up and went extinct (the actual story is somewhat different than this).
The mystery of how sexual selection does not get selected against is usually solved with what is called the “Sexy Son Hypothesis.” This was first proposed in 1979 by Patrick J. Weatherhead and Raleigh J. Robertson of Queen’s University. The idea is that females are selecting males that will provide traits to their (the female’s) sons that will get them selected by other (future) females as mates.
So the idea would not be an innate pre-existing (though subject to selection) aesthetic, but rather, a continuously refined and evolved trait of maximizing the mate-ability of one’s sons. Which makes more sense.
But still isn’t entirely right.
Source: Darwin, C. R. 1882. The descent of man, and selection in relation to sex. London: John Murray. 2nd edition, fifteenth thousand.