There’s no need to reject how biologists define the sexes to defend the view that trans women are women. When we look across the diversity of life, sex takes stranger forms than anyone has dreamt of for humans. The biological definition of sex takes all this in its stride. It does so despite the fact that there are no more than two biological sexes in any species you’re likely to have heard of. To many people, that might seem to have ‘conservative’ implications, or to fly in the face of the diversity we see in actual human beings. I will make clear why it does not.
Many people assume that if there are only two sexes, that means everyone must fall into one of them. But the biological definition of sex doesn’t imply that at all. As well as simultaneous hermaphrodites, which are both male and female, sequential hermaphrodites are first one sex and then the other. There are also individual organisms that are neither male nor female. The biological definition of sex is not based on an essential quality that every organism is born with, but on two distinct strategies that organisms use to propagate their genes. They are not born with the ability to use these strategies – they acquire that ability as they grow up, a process which produces endless variation between individuals.
