Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [57]
Why should the female reproductive tract be such an unwelcoming environment for sperm? Holman and Snook speculate that one possibility is that females are using their own reproductive organs as a screening device, making the sperm from various males run (or swim) a gauntlet of tests before being allowed to fertilize the eggs. In other words, cryptic female choice could explain the evolution of a seemingly nonfunctional cell type. The criteria that the females might use to distinguish among suitors are not well understood. It may be that, as with the exceptionally long tails of the giant sperm in D. bifurca, parasperm are a kind of secondary sexual trait, like the peacock tail.
An answer to the question of why sperm are so variable, as well as how likely it is for females to sort through sperm in their reproductive tracts and the function of all those chemicals in the semen, will likely require examining the situation from the sides of both males and females. The fierce activity that occurs inside a female after copulation does, however, provide a possible insight into that sex difference in postcoital behavior. With all that commotion going on in there, who could sleep?
Chapter 6
So Two Fruit Flies Go into a Bar...
AS SOMEONE who works on sexual behavior in animals, I've grown used to getting a lot of off-the-wall questions from curious members of the general public. Topping the list is homosexuality and whether it occurs in species other than our own. (Another inexplicably popular area of inquiry is whether animals exhibit oral sex. I still have no idea why people want to know the answer to this, and have always been afraid to ask.) And any media mention of homosexual behavior in animals always garners lurid headlines and stimulates acrimonious on-line debates. In 2007, for instance, news that scientists induced homosexual courtship in male fruit flies by changing the levels of a chemical that is key to many processes in the nervous system was greeted with predictable tabloid hyperbole: "Scientists make fruit flies gay, then straight again." On science and gay rights blogs alike, discussion raged about whether this meant that a drug altering sexual orientation would, or should, be developed by the demon Big Pharma. Others trotted out well-worn arguments about whether sexual orientation is learned or genetic and about its existence elsewhere in the animal kingdom, and then meandered into why places with large contingents of gays—such as San Francisco and Boulder, Colorado—are often such nice places to live.
Similarly, every time the issue of gay marriage rears its head, animal homosexuality comes up, in part because arguments against gay marriage often invoke phrases such as "natural order," "natural law," or "crime against nature," which make it, well, natural to wonder about whether birds—and even the bees—do that, too. And marriage aside, animals have always featured more generally in discussions of how "natural" homosexuality in humans might be, although which side their behavior is used to support differs. On the one hand, some gay activists have pointed to the widespread occurrence of same-sex courtship among animals from penguins to whales as evidence of it being part of the natural spectrum of acceptable behaviors. Animals are also sometimes used to bolster the argument that sexual orientation is not a choice but a genetically influenced, or even genetically determined, trait. Some conservatives, on the other hand, feel that animals exhibiting a distasteful behavior just underlines its debased nature. Simon LeVay, a prominent researcher in the genetics of sexual orientation, throws up his hands: "The question