11. The Lobster's Posture

In a tank in the Department of Neurobiology at Harvard Medical School, a lobster hangs in the water, held just still enough for a fine needle. Edward Kravitz, Margaret Livingstone, and Ronald Harris-Warrick are not studying the lobster's claws or its shell. They are studying its posture, and they are about to change it with a few molecules of injected chemistry. A measured dose of serotonin goes into the circulation, and the lobster's body rises. Its claws spread open. It stands high on its walking legs, a posture that in a real tank means: I am not backing down. Switch the injection to a different messenger, octopamine, and the same animal's body drops low, its claws and limbs point forward, and it holds a posture that in a real tank means retreat.

Published in Science on the fourth of April, 1980, the result was not a vague mood shift. It was a whole-body postural program, switched on wholesale by one molecule and its opposite switched on by another. The team confirmed this was more than a surface impression by recording directly from the ventral nerve cord — the chain of nerve tissue running along a lobster's underside, doing the job a spinal cord does in a human, though built on a different architectural plan. Motoneurons, the nerve cells that give muscles their final marching orders, fired in opposing, coordinated patterns depending on which of the two chemicals was circulating. The posture was not incidental to the chemistry. It was the chemistry, expressed in muscle.

Serotonin and octopamine both belong to a chemical family called amines — small molecules built around a nitrogen atom, cheap for a nervous system to manufacture and well suited to broadcasting a signal rather than whispering it to one neighbor. The lobster experiment mattered because it showed these two amines acting as opposites, not merely as two items on a longer list of things a nervous system happens to make. One says: hold this posture. The other says: hold the opposite one.

The finding held up beyond the lab's original animals. Later work on the squat lobster Munida quadrispina — a species in the Anomura, family Galatheidae, a different branch of the decapod tree from the true lobsters and crayfish of the original paper — found the same opposition between the same two molecules. Decapod is simply the name for the crustacean group that includes lobsters, crabs, shrimp, and their squat-lobster relatives, walking on ten legs more or less. That the postural switch reappears across that group, rather than sitting in one species as a curiosity, is what turns a single striking experiment into a conserved piece of nervous-system architecture.

Octopamine has long carried a tidy label: the invertebrate's version of noradrenaline, the arousal-and-alertness messenger that runs the vertebrate fight-or-flight response. Gáspár Jékely, working at the Living Systems Institute in Exeter, showed the real picture is less tidy and more interesting. Comparing genomes across the invertebrate world — echinoderms and their relatives, mollusks and earthworm-type animals, arthropods and roundworms, and a small marine worm called Meara stichopi that sits on its own separate branch of the animal tree — Jékely found working copies of adrenaline-type receptors distributed across all of them, not replaced by octopamine receptors but coexisting alongside them.

That distribution places noradrenaline-type signaling in the last common ancestor of essentially all bilaterally symmetric animals, a lineage that predates the protostome-deuterostome split, conventionally dated above 600 million years ago. Octopamine did not evolve to replace noradrenaline in invertebrates, the way an older, tidier textbook line once had it. Both systems, and a close chemical relative called tyramine, appear to have run side by side since deep in the animal family tree, with different lineages leaning more heavily on one or the other. Nobody has published a rebuttal of this reconstruction; it stands as a correction to the older, simpler story rather than a live dispute.

Borrowed for an Argument

None of that is where the lobster experiment became famous. In his 2018 book 12 Rules for Life, the psychologist Jordan Peterson, of the University of Toronto, took Kravitz's finding somewhere its authors never claimed to send it. Lobsters and humans, he argued, diverged roughly 350 million years ago; lobster dominance hierarchies run on serotonin in a way he treated as directly analogous to human status hierarchies; and this shared biology, in his reading, shows that human hierarchy is a natural, evolved fact rather than a purely cultural or political arrangement. On Britain's Channel 4 News, he framed the same logic as a matter of inevitability — continuity between how animals and humans organize their social structures being, on his account, simply what evolution predicts, not something culture invented from nothing. No new experiment backs any of this. It is a popular synthesis, built on the Kravitz lineage of lobster research and extended to humans by analogy.

Leonor Gonçalves, a neuroscientist at University College London, took the analogy apart in January 2018. Her first objection is architectural: the brain structures serotonin acts on in vertebrates are far more varied than anything in a lobster's nervous system, and a lobster does not have a centralized brain in the vertebrate sense at all — it runs on ganglia, clusters of nerve cells strung along the body rather than gathered into one organ, and it has no amygdala, the almond-shaped vertebrate structure most tied to fear and emotional weighting. Her second objection is directional: the same molecule points different ways in different animals. Lower serotonin correlates with less aggression in lobsters, but in humans, weaker communication between the amygdala and the frontal lobe under low serotonin tends to impair emotional control and increase aggression instead — the opposite direction of effect from the same chemical shortage.

Gonçalves adds a pharmacological point and a comparative one. Prozac, a drug that blocks serotonin from being reabsorbed at nerve endings, does the same molecular job in a lobster's nerve terminals as it does in a human brain, and does not make a lobster anything a reasonable observer would call happier: chemical similarity is not psychological equivalence. And for a comparison animal exactly as distant from humans as the lobster, she points to honeybees, whose natural hierarchy is matriarchal — males are driven out of the hive and die shortly after mating. If biology alone dictated one correct social structure, it is not obvious why insects and crustaceans, running much of the same old chemical toolkit, should end up prescribing such different ones. Gonçalves places the lobster/human split at the same rough 350 million years Peterson uses, but frames the one confirmed shared inheritance from that ancestor differently: not nervous-system wiring, but a digestive-system landmark, that ancestor being essentially the point at which animals first evolved a gut.

PZ Myers, an evolutionary developmental biologist at the University of Minnesota Morris who writes the blog Pharyngula, went after the number itself. Across two posts in January 2018 — the second built on a full argument from an anonymous colleague, whose work Myers published and endorsed without reservation — Myers argued that Peterson's 350-million-year figure is wrong by a wide margin. Arthropods and chordates were already separate phyla by the Cambrian, roughly 550 million years ago, and molecular-clock estimates place the actual split closer to 800 million years — a discrepancy of somewhere between two hundred and four hundred and fifty million years, depending which end of the range is used for comparison.

Myers's deeper objection is about what running on serotonin is even evidence of. Serotonin is used by essentially every animal with bilateral symmetry, and by some plants, fungi, and amoebae besides, so finding it in both a lobster and a human says very little on its own — it is the chemical equivalent of noting that both animals use water. Lobsters, he stresses, do not have brains in the sense vertebrates do. And hierarchy's shape is not fixed even among humans' nearest relatives: bonobos, genetically close to both chimpanzees and humans, run a promiscuous, female-led social system on brain chemistry barely distinguishable from a chimpanzee's strictly male-dominance-ranked one. Shared chemistry sets a capacity for social structure. It does not write the structure's rules; in humans especially, culture does that part of the job.

It is worth noticing that Gonçalves and Myers do not even agree with each other about where Peterson goes wrong. Gonçalves accepts his 350-million-year figure and argues the analogy fails anyway, on architecture and on direction of effect. Myers rejects the figure itself as an elementary error. Two named specialists, converging on the same verdict that the argument fails, by two different and only partly compatible routes — which is a healthier sign for the underlying science than if every critic had recited an identical objection.

The critique traveled well past professional biology. Nieve Brydges, writing as a science columnist for Varsity, the University of Cambridge's student newspaper, published a 2022 piece granting a roughly 500-million-year vertebrate/invertebrate split, with lobsters diversifying some 150 million years after that base divide, and still finding the argument broken on its own terms. Evolution, in her framing, is not a goal-directed climb toward some improved final form, the way a game character advances by leveling up. A hierarchy that survived natural selection is not thereby a template worth imitating, and cooperative, egalitarian social structures survive natural selection just as well as strictly ranked ones do. Biology, she concluded, supplies no license for treating any one arrangement as the uniquely natural one. Brydges is flagged here as a non-specialist voice, not a research source, but her column shows how far downstream of the original biology this argument traveled, and how many independent readers kept finding the same seams in it.

What actually survives all this scrutiny is narrower than the popular version, and more interesting for being narrower. Serotonin and octopamine really do set opposite postures in decapod crustaceans, wired down to the motoneuron. The amine-signaling toolkit really does trace back to the last common bilaterian ancestor, older than the animal kingdom's split into separate body plans. What does not survive is the leap from that toolkit to a verdict about human society. A shared molecule, redeployed by different nervous systems for different jobs, is a story about evolutionary reuse — an old word borrowed into a new language, not the same sentence repeated. It sets what a nervous system is capable of. It does not set what a society is required to be.

The lobster's flexed posture lasts only as long as the serotonin does, and drops the moment a bigger claw enters the tank. Rank, even in a lobster, is a state, not a sentence. Further along the same nerve cord runs a different ancient amine, tuned not to posture but to pursuit — the molecule that carries this journey forward, from standing one's ground to wanting something in the first place.

Overturned if: a decapod crustacean is found in which octopamine produces the dominant flexed posture and serotonin the subordinate one — reversing rather than repeating the Kravitz pattern and breaking the cross-species conservation the squat-lobster replication currently supports.

Sources

• 1980 · Livingstone, Harris-Warrick, Kravitz, "Serotonin and Octopamine Produce Opposite Postures in Lobsters" — Science
• 2017 · Jékely, "Ancient Coexistence of Norepinephrine, Tyramine, and Octopamine Signaling in Bilaterians" — BMC Biology
• 2018 · The Conversation, "Psychologist Jordan Peterson says lobsters help to explain why human hierarchies exist – do they?" (quoting Jordan Peterson and Leonor Gonçalves, UCL) — The Conversation
• 2018 · Myers, "Lobsters are not people" — Pharyngula/FreethoughtBlogs; companion post, "Jordan Peterson does not understand evolution, nervous systems, or logic" — Pharyngula/FreethoughtBlogs
• 2022 · Brydges, "Botched biology: how does Jordan Peterson use science to prop up his (mis)beliefs?" — Varsity