Jen

I have a couple of quibbles with this post, as someone who studies sexual selection in living dinosaurs. I think your post is a little too complicit with the distorted “Mad Men” idea of sexual selection that is so popular in the. . . popular literature. It’s kind of a pet peeve of mine.

First, as can be seen in the paper in PLOS 1 (thanks for the link!), the authors only found the skulls. So, no one actually knows which sex these crazy skulls belonged to. They could have been female. There are, in fact, many species of birds in which the female is larger, more ornate, and more promiscuous. There are even more cases of “reverse” sexual dimorphism in fish, insects, and reptiles. So many, in fact, that if we weren’t mammals (in which all females pay an extraordinarily high gestation cost), we probably wouldn’t call it “reverse” dimorphism at all.

Second, the idea that sperm is cheap and eggs are expensive is not really accurate. It’s not fair to compare one sperm to one egg. Really, one should compare the two sexes’ investments over the reproductive bout. It is true that many females invest more in reproduction than males, but that is probably because they control the site of fertilization, and thus are more certain that the offspring they are caring for are their own. In species where one sex is promiscuous, it is inevitably the one that has less certainty about paternity, regardless of whether or not their gametes have flagella. George Williams has a section on this in his classic book “Adaptation and Natural Selection”. It would be tiresome to cite too many examples, so I’ll just mention two factoids: in some Drosophila species, the male ejaculate contains a single, meter-or-more-long sperm; and in Syngnathid fish (seahorses et al.), fertilization occurs in the male’s pouch, and females are larger, showier, more aggressive, and more promiscuous.

Quibbles or rant? You decide.