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In his book 12 rules for life Jordan Peterson claims that:

Consider serotonin, the chemical that governs posture and escape in the lobster. Low- ranking lobsters produce comparatively low levels of serotonin. This is also true of low- ranking human beings (and those low levels decrease more with each defeat). Low serotonin means decreased confidence. Low serotonin means more response to stress and costlier physical preparedness for emergency—as anything whatsoever may happen, at any time, at the bottom of the dominance hierarchy (and rarely something good). Low serotonin means less happiness, more pain and anxiety, more illness, and a shorter lifespan—among humans, just as among crustaceans. Higher spots in the dominance hierarchy, and the higher serotonin levels typical of those who inhabit them, are characterized by less illness, misery and death, even when factors such as absolute income —or number of decaying food scraps—are held constant. The importance of this can hardly be overstated.

at another passage he claims that:

A lobster with high levels of serotonin and low levels of octopamine is a cocky, strutting sort of shellfish, much less likely to back down when challenged. This is because serotonin helps regulate postural flexion. A flexed lobster extends its appendages so that it can look tall and dangerous, like Clint Eastwood in a spaghetti Western. When a lobster that has just lost a battle is exposed to serotonin, it will stretch itself out, advance even on former victors, and fight longer and harder.

For the second passage he cites the following paper

While there are many papers linking position in the social hierarchy in primates and humans I could not find a paper supporting the first passage.

The best I could find to support the first passage is an interview with Bret Weinstein where they mention that Peterson is indeed correct claiming that social hierarchy of lobsters in linked to serotonin levels. Interview with Bret Weinstein

A review paper claims that:

Is the marine environment less conducive to the establishment of dominance hierarchy structures, or does this just underline the lack of detailed behavioral information about most marine invertebrates?

Which suggests that not much is known about the relationship between serotonin levels in lobsters and the position in the social hierarchy.

Peterson basically argues that since the injection of serotonin leads to aggressive behavior in invertebrates, which is dominant trait in the animal kingdom this is proof that serotonin is indicated by the status in the social hierarchy. However It could just as well be that serotonin just leads to aggressive behavior in lobsters without being an indicator of the position in the hierarchy.

Are there any studies which specifically investigate whether the position of lobsters in a hierarchy is reflected in their serotonin levels?

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The paper Peterson cites about serotonin and lobsters explicitly contradicts him in two major ways. First, although serotonin plays a role in aggression across many species, its role is not the same across those species:

The nature of the linkage [between serotonin and aggression], however, is not simple, and it has proven difficult to unravel the role of the amine in the behavior. In vertebrates, lowered levels of 5HT (endogenous or experimentally induced) or changes in amine neuron function that lower the effectiveness of serotonergic neurons generally correlate with increased levels of aggression (19, 20) whereas in invertebrates, the converse is believed to be true (11–13). Genetic alterations of amine neuron function also can change aggressive behavior in animals (21–24) and in people (25–27) although, again, in most cases, it is not clear how the genetic change is linked to the behavior. ... Finally, direct injections of amines like 5HT into animals also cause changes in aggression, but even here the relationships are complex. For example, in ants, injections of 5HT and its precursors lower interspecific aggressiveness toward intruders but raises intraspecies aggression (28, 29).

Clearly, the role of serotonin plays in aggressive behavior is not conserved between lobsters and humans. The most we could say is that serotonin plays some role in regulating aggression, but that role changes between species.

Secondly, the same study observed that although lobsters injected with serotonin will fight for longer, but are not more to start a fight or to win:

Thus 5HT selectively decreased the likelihood that subordinates withdraw from the attacks of their dominant opponents without altering their locomotor activity, the rules of escalation of fights, or the eventual outcome of an encounter.

Peterson is directly contradicting the conclusions of the paper he is citing:

A lobster with high levels of serotonin and low levels of octopamine is a cocky, strutting sort of shellfish, much less likely to back down when challenged.

Either he is a liar or does not understand the paper he is citing, and I can't decide which is worse.

P.S. Here is a video thoroughly dismantling Peterson's entire philosophy. The part about him being incorrect about lobsters at 40:00.

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    $\begingroup$ You did not answer the question if there are studies linking the position in the social hierarchy to serotonin levels. $\endgroup$ Feb 28, 2023 at 6:58
  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Biology Meta, or in Biology Chat. Comments continuing discussion may be removed. $\endgroup$ Mar 1, 2023 at 3:46

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