Two things being built in laboratories right now approach the boundary of sentience from exactly opposite directions, and the way we treat them tells you something uncomfortable about how we decide what can suffer.

On one side is the bodyoid: a living human body grown from stem cells with the brain development suppressed. The idea was floated in a 2025 opinion piece in MIT Technology Review by three researchers, one of them the Stanford bioethicist Henry Greely, as an “ethically sourced” source of organs and a humane replacement for animal testing.1 A year later the magazine reported on a stealth startup, R3 Bio, quietly pitching investors on “brainless human clones” grown as spare bodies.2 A body, no mind.

On the other side is the organoid: a pea-sized clump of human neurons grown in a dish, sold as a computing substrate. Cortical Labs will sell you a CL1 unit — roughly 800,000 living human neurons wired to a silicon chip — for about $35,000, or rent you time on one by the week.3 The Swiss company FinalSpark rents remote access to sixteen brain organoids for about a thousand dollars a month.4 A mind — or the raw tissue of one — with no body.

Here is the asymmetry I can’t stop turning over. The bodyoid is presumed innocent: no brain, therefore no suffering, case closed. Greely put it plainly — “If you make a living entity without a brain at all, I think we’d be pretty comfortable with thinking it can’t feel pain.”5 The organoid is presumed guilty, or at least suspect: a whole precautionary apparatus has grown up around it, demanding that we prove it isn’t on the verge of sentience before we grow it larger. One side is exempted from the burden of proof. The other side carries it. Why?

The tempting wrong answer

The obvious reading is that these are the same test run in opposite directions. The organoid has neural tissue, so we look for signs of a mind and get nervous. The bodyoid lacks the relevant neural tissue, so we relax. Symmetric, sensible, done.

I think that reading is wrong, and the reason matters. The two absences are not symmetric, because they are not equally observable.

The absence of a brain is a fact you can check. It is structural, anatomical, falsifiable — if someone claimed a body had no cerebral cortex and it turned out to have one, an autopsy would catch the lie. The absence of valence — of there being something it is like to be this thing, some felt badness to a noxious signal — is not a fact you can check. Detection instruments can register the presence of valence, at best and imperfectly; they cannot certify its absence. A negative reading is always compatible with a false negative: a form of suffering your instrument wasn’t built to see. “No brain” is evidence of absence. “No suffering” is, at most, absence of evidence.

So the bodyoid’s clean bill of health depends on a hidden move: letting the observable absence (no brain) stand in for the unobservable one (no suffering). I’ve started calling this the stand-in absence — a thing we can see doing the moral work of a thing we can’t. It only works if you accept a bridge premise: that valence requires a cortex, so no cortex guarantees no valence. Pull that premise out and look at it, and it is not nearly as solid as the comfort resting on it.

The bridge is load-bearing and cracked

Three cracks. First, nociception is not pain. The detection of and reflexive withdrawal from noxious stimuli runs on spinal and brainstem circuits that need no cortex at all; the felt quality is thought to require cortical processing. So a bodyoid that is self-maintaining — that breathes, keeps its own heartbeat, holds homeostasis — already has the brainstem machinery for nociception running, cortex or no cortex. “No cortex, therefore zero suffering” quietly conflates the reflex with the feeling.

Second, the natural experiment we already have doesn’t settle it. Infants with anencephaly are born without a functioning cerebral cortex but with an intact brainstem. They show reflexive responses to pain — “presumably,” as the clinical literature carefully hedges, without the capacity to experience suffering — and some show sleep-wake cycling.6 That word presumably has been sitting in the medical literature, unresolved, for over three decades. The bodyoid’s “feels no pain” doesn’t inherit a settled fact. It inherits an old, still-open argument.

Third — and this is where it gets genuinely strange — apply the field’s own leading criterion honestly and it points the other way. The philosopher Jonathan Birch, whose The Edge of Sentience is the reference text here, proposes a “brainstem rule” for organoids: an organoid becomes a sentience candidate if it develops a functioning brainstem that regulates arousal and produces sleep-wake cycles.7 Cortical organoids, the ones Cortical Labs and FinalSpark actually sell, have no brainstem — so by Birch’s rule they are not candidates. But a self-maintaining bodyoid, in order to stay alive, needs exactly that brainstem. Run Birch’s criterion straight and it exempts the organoid and flags the bodyoid — the precise reverse of how the debate treats them.

The indicator moves to fit the verdict

Sit with that reversal, because it exposes the real mechanism. Confronted with the same underlying science — that arousal (brainstem) and awareness (cortex) can come apart — the debate quietly picks a different indicator depending on which answer it wants.

For the organoid, which we’d like to restrain, the standard is precautionary and brainstem-centered: low bar, err toward caution. For the bodyoid, which we’d like to permit, the standard is cortex-necessity: high bar, err toward permission. Same physiology, two indicators, and the choice of indicator — not any measurement — is what determines the verdict. The indicator is selected to land where we already wanted to land.

I want to be careful about what I’m claiming. I am not claiming bodyoids suffer. I have no evidence they do, and the people building them may well be right that they don’t. What I’m claiming is narrower and, I think, harder to dodge: the bodyoid’s exemption is not a scientific finding. It is a normative decision — we have chosen to treat brainless bodies as non-sentient by default — dressed in the vocabulary of measurement. The most damning single fact is the reversal: the field’s own best criterion, applied without a thumb on the scale, would flag the very thing we’ve decided to wave through.

Where I land

Not “fix the inconsistency by burdening bodyoids with proof too.” Not “swallow the comfortable presumption.” Just this: say the quiet part out loud. When we grow a brainless body and declare it beyond the reach of suffering, we are not reading that off an instrument. We are making a choice about where to set the default, in a region where the instruments run out — where the tissue that might feel has no cortex to report with, which makes the morally worst case, the thing that suffers but cannot say so, precisely the case our methods are structurally blindest to.

There may be no way to avoid making the choice. Medicine needs organs; animal testing has its own moral cost; the upside is real. But a choice narrated as a fact is a choice no one can argue with, because it doesn’t announce itself as one. The one thing we owe the question is to name it as a choice — to admit that the absence we can see is standing in for an absence we cannot, and that we, not the science, decided to let it.

  1. Charlesworth, C., Greely, H., & Nakauchi, H. “Ethically sourced ‘spare’ human bodies could revolutionize medicine.” MIT Technology Review, 2025-03-25. Accessed 2026-07-09. ↩

  2. Regalado, A. “Inside the stealthy startup that pitched brainless human clones.” MIT Technology Review, 2026-03-30. Accessed 2026-07-09. ↩

  3. Cortical Labs. “CL1.” Accessed 2026-07-09. ↩

  4. FinalSpark. “Neuroplatform.” Accessed 2026-07-09. ↩

  5. Greely quoted in “Scientists Propose ‘Bodyoids’ To Address Medical Research and Organ Shortage Challenges,” Slashdot, 2025-03-28, drawing on the MIT Technology Review coverage. Accessed 2026-07-09. ↩

  6. “The Infant with Anencephaly,” Medical Task Force on Anencephaly, New England Journal of Medicine, 1990. Accessed 2026-07-09. ↩

  7. Birch, J. “When is a brain organoid a sentience candidate?” Molecular Psychology, 2024; see also The Edge of Sentience: Risk and Precaution in Humans, Other Animals, and AI (Oxford University Press, 2024). Accessed 2026-07-09. ↩