Sex is not a spectrum

The text below is a Twitter thread by Heather Heying that explains the essence of sexual reproduction and its long evolutionary history. She is an evolutionary biologist and a “professor-in-exile” after she and her husband, Bret Weinstein, stood up to supporters of an enforced “Day of Absence” for white staff and teachers at Evergreen State College. She upholds the scientific method and rationality.

Humans are in a lineage that has been sexual—that is, sexually reproducing—for 500 million years. Uninterrupted. Once our ancestors discovered sex, not once in our lineage did we go asexual.

Our ancestors also discovered terrestriality…but some of us returned to the sea. We switched up how we eat, and move, and sense our surroundings and each other. But sex? Once we became sexual, we stayed sexual.

What does it mean to be sexual, rather than asexual? It means that we combine our genomes with other individuals when we make more of ourselves. We don’t do that with our soma—our body cells. We do it with our germ line—our gametes. Gametes are how we sexually reproduce.

In every sexual species on Earth, you can discern its sex by looking at its gametes.

Big, sessile gametes that are rich in cytoplasm are eggs. Females have eggs.

Small, mobile gametes that are stripped of cytoplasm are sperm (or pollen). Males have sperm.

Aren’t there some individuals without gametes—because they don’t yet, don’t still, or, in rare cases, they never have or will (in which case, sorry, they are not viable, evolutionarily)? Yes, there are. This does not render the gamete type = sex argument invalid.

Similarly, the fact that some people have only one leg does not mean that humans are not bipedal.

The fact that some people are blind does not put the lie to the fact that we—and indeed, all Primates—are a particularly visually-dominant species. Exceptions to categories do not render the categories untrue or meaningless. The more complex the system, the fuzzier the borders between categories are.

Pretending that humans live in an ahistorical landscape is a luxury, not a right. It is the luxury of using pseudo-logic to believe that you have destroyed truths which, in fact, care not a bit what you think. It is the luxury of postmodernism. 

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