Posted: Mar 23, 2011 7:24 pm
Gallstones wrote:The upsuck hypothesis doesn't work.
The semen has to be there before the orgasm (in the female) but if the semen is already there the male is done and there will not be any more stimulation for the female--which she will need in order to have an orgasm.
Not necessarily as the female can still reach orgasm by rubbing against the male. Or masturbation.
And it is meant to work if she orgasms from one minute before the male (and up to 45 minutes after).
But I agree that it isn't very convincing.
Then again, if a male is holding on waiting for the female and she orgasms and he obviousy knows it then he is not likely to be taking much longer himself so a minute could be plenty of time for him.
Gallstones wrote:It could work if simultaneous orgasm was the norm.
It's really too bad too, because if upsuck increased the facilitation of fertilization, easier orgasm during coitus would be present in females.
Only if the male is 'good quality' and the female is in the peri-ovulatory period. Otherwise with the former the female would be better to avoid orgasm and in the latter there would be no egg to fertlize.
Gallstones wrote:Antlers could have been sex linked at the outset, just as calico and tortoiseshell color is in cats.
They appear to be sex-limited in that the expression of the genes for antler growth are regulated by tesoterone so are autosomal genes carried by both sexes ie not on the 'X' chromosome.
'Sex-linked' is when it is the female having two 'X' chromosome genes because she has two 'X's, and the male only one gene on his single 'X' as with the cat colours.
It is considered that when a novel trait arises on autosomal genes that both sexes can express that trait initially before the different selection pressures act for or against the trait depending on sex. Sex hormones are the usual mechanism.
Something different has evolved in the caribou and the antlers grow soon after birth,at least parltly because they don't grow from androgen-dependent pedicles.
The ovaries do produce an oestradiol hormone which acts like testosterone and is connected to the casting of the antlers.
Caribou only diverged about 2million years ago.
It is interesting considering how traits that are sexually dimorphic arise and sex-limiting mechanisms come into play.
In peafowl females removing the ovaries causes the development of the showy male plumage.