Last November, Kori Doty, a B.C. parent, gave birth to a baby named Searyl. Kori Doty, who has a mustache and light beard, identifies as a non-binary trans person – neither male nor female – who prefers to be called "they." They want to raise the child as gender-neutral, and are fighting to omit the child's gender from all official records.

In Saskatchewan, Dustin Dyck also wants gender markers removed from birth certificates. His teenager, Jordyn, identifies as non-binary, and he believes that Jordyn would have had an easier childhood if Jordyn had not been identified by gender. Another parent, Fran Forsberg, has filed a complaint with the provincial Human Rights Commission because the Vital Statistics Agency has refused to change the gender of her child, Renn on Renn's birth certificate. (Renn, who is nine, was born a boy but identifies as a girl.) Then there's Renn's brother Tana, 12, who identifies as two-spirited and gender-fluid. "It doesn't state who they truly are," she told the CBC, of her children's IDs.

Leah McLaren: Today's kids still feel the pressure of gender expectations

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Across Canada, people are requesting governments to retroactively change the sex listed on their birth certificates, or to have themselves retroactively declared "non-binary." Provincial governments are attempting to comply. Part of this is an effort to be socially progressive; part is fear of running afoul of new human-rights legislation that protects transgender rights. As David Arnot, chief commissioner of the Saskatchewan Human Rights Commission, says, a judge could reasonably decide that in some cases, gender signifiers – even on a birth certificate – violate a child's human rights.

The arguments for altering or scrapping gender identification are manifold. Biological sex is irrelevant, goes one; it's how you self-identify that counts. By not forcing people into "his" and "hers" boxes, goes another, we will reduce stereotyping and advance equality. At the root of these arguments is the belief that the very concept of a "gender binary" is false, harmful, and archaic.

The doctrine of non-binaryism holds that biological sex has nothing to do with gender, that gender exists along a continuum, and that the differences between the sexes are socially constructed. Babies are born as blank slates, and the extent to which they identify as male or female depends on their environment. Evolution plays an insignificant, if any, role in sex differences, and even the obvious differences in reproductive function are incidental to people's self-identity. (Confusingly, transgender activists often argue that their gender identity is hard-wired, and that children who identify as the other sex were "born that way.")

It seems ridiculous to have to argue this, but the science is settled. The two biological sexes (and there are only two) are broadly (though by no means perfectly) coterminous with gender. This holds for nearly every species in the animal kingdom, even us, and for all societies on Earth. Close to 100 per cent of the human race is born with a set of either male or female chromosomes. A small number of people are born with chromosomal and/or reproductive abnormalities, and these people are commonly identified as "intersex."

Many sex differences are biological, and they matter. Sexual differentiation is driven by sexual reproduction, which is the basic mechanism of animal evolution. It's the way that animals get together and pool their DNA. Anyone who claims that sex differentiation is a socially constructed myth, or doesn't matter, must have flunked Biology 101. As current research shows, even our brains are different.

None of this is to argue that we should force people to conform to gender stereotypes, or punish them if they don't. If people want to identify as transgender, fine. If they want to raise their kids in a gender-neutral way, fine. If they want to self-identify as polygender, demigirl, or transmisogyny constrained – well, whatever. (Let's just please, please leave the kids alone. The research says that most kids with gender issues resolve them by puberty.)

In other words, changing people's birth certificates may make them feel better. But it doesn't change the facts. You can say your eyes are brown. But if your eyes are blue, that doesn't make it so.