https://twitter.com/RichardDawkins/status/178678872412412757...
You can debate him there if this is your hobby horse.
This isn't in fact my hobby horse so without more specifics I'll just treat him as talking past people and move on.
Looking at the video in the second link, it looks like he only spent three minutes talking about trans people and I don't see any explanation there about how you're supposed to apply his universal biological definition to individual people.
"It happens to be embryologically DETERMINED by chromosomes in mammals and (in the opposite direction) birds, by temperature in some reptiles, by social factors in some fish."
Sometimes you don't get gametes. At that point, you either need to exclude those people from your classification system because it's ill-suited for this task, or you need to make your classification system significantly more complicated because there's a lot of edge cases.
> the nature of sex (spectrums and such)
Sex shows itself to be a spectrum pretty often.
> unscientific claims about being able to change one's sex
Phenotype or genotype?
They don't always match even without any medical intervention, and a change in hormones can drastically change phenotype.