Looking through some of the drafts clogging the blog, I decided to whittle away at the queue. I started this months ago. It’s here now, not particularly in sync with the season or recent topics, but I like Sapolsky.

‘Biology is destiny’, say the Christian Right, the bland bureaucrats of morality, the loud whisperers at Sunday school. They want gender to be a tomb carved in marble: you’re assigned at birth, and you stay a perfect statue. But Sapolsky waltzes in and says, ‘Hold up – what do you mean by biology? Which biology? Which markers count?’

In the clip above, Sapolsky unpacks neurological evidence that upends the essentialist cheat codes. He doesn’t pretend we now have the final answer to gender. He does something scarier to fundamentalists: he shows just how messy biology is.

The Bed Nucleus, the Finger Ratio, and the ‘Wrong Body’ Hypothesis

Sapolsky discusses three pieces of neurobiological evidence:

1. Digit ratio (2nd vs 4th finger length): In lesbians, on average, the ratio is closer to what you see in straight men than straight women. That’s a correlation, an eyebrow-raiser, hardly a decree.
2. Acoustic reflexes (auto-acoustic reflex): Another early finding in women’s sexual orientation, though faint and underexplored.
3. The bed nucleus of the stria terminalis (BSTc): Here we reach heavy artillery. There is a neuron population in this region that, on average, is about twice as large in males as in females. In postmortem analyses of trans women (male → female), this region’s size corresponds to their identified gender, not their natal sex. Crucially, that alignment is seen even in trans individuals who never underwent full hormone therapy or surgical changes.
   • Sapolsky recounts astute controls: men treated (for, say, testicular cancer) with feminising hormones don’t show the same shift.
   • Also, using the phantom-limb analogy: men who lose their penis to cancer often report phantom sensations; trans women rarely do. That suggests the body map in the brain never fully “registered” that organ in the same way.

He doesn’t overclaim. He doesn’t say, ‘Case closed, biology proves everything’. He says: These data complicate your neat categories. They force you to ask: which biological measure do you privilege? Hypertrophied neurons? Chromosomes? Receptor density? Hormones? All of them simultaneously? None of them?

Essentialism as a Trap

Fundamentalists and anti-trans ideologues deploy essentialism because it’s convenient. They demand an ironclad ‘essence’ so they can exclude anyone who fails their test. But what Sapolsky shows is that essence is simply a scaffold; we get to pick which biological scaffolds we accept. They may choose genes and genitals; the neurobiologist gives them neuron counts and brain-maps. When your ideology elevates one scaffold and ignores the others, it betrays its own contingency.

Moreover, the evidence suggests that identity, experience, insistence (in Sapolsky’s language: ‘insisting from day one’), and internal brain structure might converge. The ‘wrong body’ isn’t a metaphor. It’s a mismatch between internal brain architecture and external form. The stubborn fragments of biology that fundamentalists accept are torn by the dissonance that science increasingly reveals.

What This Means for Trans Rights, Discourse & Strategy

• Science is never ‘conclusive’. Sapolsky offers compelling support, not gospel. Anyone claiming this settles everything has never looked at a scatter plot.
• Lived experience still matters. Even if we never had brain slices, self-reports, psychology, psychiatry, anthropology, narratives remain valid. Brain studies supplement, not supplant, testimony.
• Essentialist opponents have boxed themselves in. When they demand biology decides everything, they hand the baton to neuroscientists – and neuroscientists keep running with it. The entire ‘biology’ equals only what I like’ regime is exposed.
• Ambiguity is a strength, not a liability. If we insist identity is linear and tidy, we re-enact their demand for purity. Recognising complexity, mess, and variance is radical resistance.