The essential difference is that if a female gamete is very expensive, male gametes are really rather cheap. Consequently, a female will not benefit by mating lots of times, because her fecundity is limited by how many eggs she can produce. A male will benefit by mating with lots of females, because his fecundity is not limited by his ability to produce gametes. And in the beast that I worked with, Drosophila subobscura, it was very striking, that the female mated once in her life, a male could mate five times a day. And their attitudes, if I can put it that way, towards mating, were very different. The male... female is extremely choosy and selective, not only would she only mate with members of her own species, but they had to be the right age, they had to be fit and healthy, and she had methods of discovering whether they were fit and healthy though the courtship dance. The males were... you could get a male to attempt to mate with a blob of wax on the end of a bristle that you moved in the right way, he'd dance with it, and when you held it still, he'd try and mount it. I mean, he just wasn't a very discriminating organism. I'm afraid, it's what's to be expected. But once you get the formation of a pair bond, and... which lasts through a breeding season, or through life, and you get both parents investing in the offspring, then, of course, it is as important to the male as the female to select an appropriate mate. And you get these very elaborate mutual courtships in many birds, for example, where both parents are feeding the young and making equivalent contributions; except, always, of course, the female has to lay the eggs, but otherwise the male may be doing as much, to make the nest, to look after the kids. Going back to the very early ethology that Julian Huxley did on grebes, for example, where you can't tell the male and female apart by looking at them, and they have this extremely elaborate courtship in which they're both having to perform to convince the other. So it really does depend how much investment you put into your kids.