Consciousness and how it got to be that way

Sunday, July 19, 2009

What Do Serial Killers and Suicidal Rats Have in Common?

Serial murder is such an astonishingly maladaptive behavior that I've often speculated whether we're not seeing a) a gene that, when heterozygous, is adaptive, but when homozygous, can lead to this behavior, or b) a toxoplasma gondii-like infection.

Toxoplasma gondii is the pathogen that makes the rodents it infects behave (basically) suicidally around predators, like cats; the cat eats the rat, the organism survives in the cat's gut, and when the cat defecates, it spreads more Toxoplasma. (I first read about this organism and the incredibly specific behavior an infection engenders in the work of Daniel Dennett, who is a big fan of this organism as a metaphor for other replicators.) Now it turns out that humans infected with Toxoplasma are also more likely to behave dangerously, judging by car accident rates. (Hat tip to Marginal Revolution).

Humans engage in many apparently maladaptive behaviors (serial murder among them) and this story gives us no reason to conclude that serial murder is the result of an infection, but it does show that even in humans, complex behaviors can be affected by an organism in ways similar to the other host species we've studied. Behaviors like serial killing are so inexplicable that hypotheses about their origins should include infection as a possible etiology.

I grant the full-on speculative nature of this post, and even if serial killers are infected with a T. gondii-like pathogen, then it remains to be explained a) whether the infection-induced behavior would have been the same in our hunter-gatherer ancestors (how can you be a serial killer in a band of 25 people?) and b) how exactly the behavior would improve transmission, which is clear in the case of rats and cats.


  1. so would this mean that toxoplasma gondii pathogen would be present in the victim of the serial killer? and if so, how would we narrow the scope of "dangerous behaviors" to apply this to the victimology?

  2. The model is that the serial killer is infected, and in the course of attempting violence, sheds virus presumably through blood on others. Obviously the victim is an epidemiologic dead end, so my speculation is that during the paleolithic, family justice would have resulted in blood shed by multiple individuals attacking the killer, some of whom would go on to get infected. This is not necessarily with a tox but some bug with complex neurological effects, of which there are a number - hello rabies!