Female Control

"A criticism of early pioneers like Geoff Parker and me was that we were sexist because we only studied males. Male traits are much easier to study than female ones. It’s hardly surprising we researched the easy bits first. If you look at pre-copulation displays, males are much more brazen. They show off their attributes. Females are more subtle in the way they make their choices. You can’t tell what’s going on in a peahen’s head when she’s surrounded by peacocks. But you can see the males strutting and fanning. The expression ‘female promiscuity’ makes it sound like a choice. But the ornithologist Jonathan Elphick describes female ducks as being essentially gang-raped, and sometimes drowned, in the mating process. In most species, it’s a matter of choice. Female Control deals with situations in which it might not be. In the mid-1980s, the biologist Randy Thornhill suggested that females might be able to discriminate between sperm from different males after insemination. He called it ‘cryptic female choice’, to distinguish it from pre-copulatory female choice. There was no real evidence at the time that females chose between males, let alone sperm. But the evidence for sperm competition soon became better established. Eberhard provides an encyclopedia of possibilities for female control. He argues that anatomy reveals different ways in which females might control what males do. For example, a female might simply stop a male inseminating her or reject sperm altogether. We studied chickens and that’s exactly what happens. Females want to be inseminated by the dominant cockerel. If a subordinate one manages to inseminate a female then she immediately ejects the sperm in a kind of muscular twitch. Our chicken study was one of the first demonstrations of cryptic female choice. Human reproduction is much more difficult to study because you can’t do the kind of experiments that you do with chickens. So we have no real evidence. There are, however, hints. There is a huge level of spontaneous abortion in humans, almost undetected by women. One explanation is that eggs have been fertilised by the ‘wrong’ sperm. In other words, an embryo might not develop properly so the body developed a technique for aborting it and starting again. No. When behavioural ecologists describe what is going on they often use expressions that imply consciousness. But there is no question of that at all. Yes. We know that female birds can recognise certain types of sperm, probably by proteins on the sperm surface. There might be an immunological reaction that stops these sperm in their tracks. Some sperm may be more compatible with the female and encouraged through the reproductive tract. Bill’s book made people sit up and address this. No biological system is perfect. I suspect there might be sperm and embryo selection going on in humans. It’s always hard to use humans as a yardstick for anything because we’re protected by medicine. Cultural factors also come into play. The reason I’ve worked on non-humans is that those effects do not confound you. But the situations where you are most likely to detect sperm selection are those alluded to earlier, where females are forcibly mated. That’s precisely the kind of situation where the female doesn’t have a free choice. She needs a mechanism for determining who fertilises her eggs."