About a billion years ago, evolution hit on a brilliant way to fast track the number of variations that could try their hand at adapting to their environment: sex. Instead of each species giving birth to a clone of itself (meiosis), with a dash of mutation thrown into the mix for variety, two of a species could combine their genomes. (Your genome is your complete set of chromosomes.)
In one fell swoop, Nature had created her own experiment kit, where she could play with every possible permutation and combination. So that’s what evolution had to work with: two similar but not identical creatures making a third creature sharing the traits of both its parents. One parent is the male of the species whose gametes — sperm — are the mobile members of the team; the other parent, the female, keeps her gametes — eggs — closer to home. Which is how most species, fauna and flora, reproduce. Birds do it, bees do it, even educated fleas do it. And all this time — a billion years! — Nature has used two and only two versions of a species, male and female, to do her magic. Not three or four, not some fluid middle ground, just a simple binary division. Sexually, you’re male or you’re female. Period.
What could be clearer?
Your sex is defined by your gamete type — sperm or egg — which puts
you in either the mom or dad role. Which has absolutely nothing to do
with how you think of yourself. Straight? Gay? Trans? Bi?
Intersexual? Asexual? Born with ambiguous genitalia and you’re not
sure how you want to self-describe? That’s something completely
different. You might have male gametes but you feel you’re female,
you dress as a female, you call yourself a woman: then, as far as
society is concerned, you are a woman. You may even have an
operation to create a vagina where formerly there was a penis and
testicles, and you may make love as a woman. But — big but — you’re
never going to be able to give birth as a woman. Your gametes define
your role in reproduction, and nothing you can say or do will change
Having said that, whatever social role you choose to adopt should obviously (obvious to me, at any rate) be respected; it certainly shouldn’t be subject to the politics of the day. Which is why I find the current rash of anti-transgender laws so abhorrent. Currently 28 states are considering anti-trans bills outlawing gender-affirming health care to young people. Three states, Tennessee, Mississippi and Arkansas, have already passed such laws, using the bogeyman of keeping a level playing field in sports as the reason, trans girls presumably having an unfair edge on non-trans girls.
(Which, by the way, is a huge can of worms for female athletes. World Athletics, the governing body for international track and field competitions, bars women with over five nanomoles of testosterone per liter of blood from competing as females in races between 400 meters and one mile. Which, IMHO, makes as much sense as barring any players over six feet in height from the NBA. The February 2021 issue of Scientific American has the story.)
These bills all refer to the sex the kid was assigned at birth — which is sometimes a gray area, i.e. the intersex situation. Not all infants who will later produce sperm have obvious penises, and vice versa. According to this, “The most thorough existing research finds intersex people to constitute an estimated 1.7% of the population.” That is, up to 1 in 60 kids are in that ill-defined area. It’s not just ambiguous genitalia that make for intersex babies, but a bunch of other defining characteristics, including sex chromosome composition, gonadal structure, hormone levels, and the structure of the internal genital duct systems.
Bottom line: your ability to make either eggs or sperm defines your biological sex, for which humans have just two options. Everything else — ambiguous genitalia, the sense you’re in the wrong body, all the rest — define your gender, with all its many variations. We shouldn’t conflate the two, and please keep politics out of it!