Are you born with talent or do you adapt it over time? (Split from TOGS' thread)

[solecistic]

Think, I think it's important to note that a sexual ornament doesn't have to have any other purpose. There are certainly examples of traits that are both sexually ornamental and genetically beneficial in other ways, as you've clearly shown - and in those cases, it certainly makes sense for females to select for those traits. But many times - if not most times, sexual ornaments are just sexual ornaments. Instead of one trait (a large jaw) being about a very specific underlying other trait (high testosterone), a sexual ornament can exist as a window into the genome of another organism. A peacock's tail has absolutely no value except as a sexual ornament, but the fact that the peacock has a high enough energy budget to grow a magnificent tail shows that as an organism, he is genetically fit. The tail has no other use, no other purpose, and no specific underlying trait. It exists only to attract mates. The reason it works as a fitness indicator is that a very beautiful tail costs a lot of energy to grow, due to its complexity and size. A peahen who chooses a beautifully-tailed peacock as a mate is more likely to produce offspring of better quality in larger quantity, thus ensuring that her own genes will continue on for more generations.

[Think]

The tail has no other use, no other purpose, and no specific underlying trait.

I'm afraid I'm going to have to stop you there. No one knows why yet, but peacocks with superior tails are far less likely to be eaten by predators (research study by Petrie in 1992). It's not conclusive, sure, but it suggests to me it's another flag ornament, that there's a heritable trait accompanying it.

The reason it works as a fitness indicator is that a very beautiful tail costs a lot of energy to grow, due to its complexity and size.

Ok, yeah, following you here. The handicap principle. I totally agree that this can be a large part of sexual ornamentation.

Now, here's my position: I can totally see where you're coming from, but I feel that for a phenotype to be attractive within a population, it needs to have some sort of utility, at least to start with. I would agree that sexual ornaments can just be sexual ornaments, but I would argue that they originated for a reason. The structure of the male face, preference for an hourglass figure in females, preference for childlike features in female faces, preference for averagely proportioned faces - all of these desirable physical features have some sort of original practical purpose, even if they're mostly just ornaments now.

EDIT: it's funny, the only thing we're really not in accord about is the bit completely glossed over in the quote from the book you provided: "(It doesn't matter why they evolve this preference -- perhaps there was a mutation affecting their sexual preferences, or their vision happened to respond more positively to large than to small objects.)"