Researchers are studying psychopathic chimps to better understand the human variety

To understand the drivers of a psychopathic personality (marked by callousness, disinhibition and superficial charm), it's worth looking at our closest relatives. Some chimps, like some people, score highly on scales designed to evaluate psychopathic tendencies. And new work in Frontiers in Neuroscience reveals a potentially important genetic contributor to psychopathic traits in chimps, which could lead to a better understanding of the traits in people.

The team led by Robert Latzman at Georgia State University studied 164 chimpanzees housed at the Yerkes National Primate Research Center in Atlanta, Georgia and the National Center for Chimpanzee Care at the University of Texas. Each chimpanzee was rated by typically two to three colony staff members, who knew the individual animals, on the "CHMP-Tri scales" (a kind of chimp personality questionnaire that assesses their boldness, meanness and disinhibition – the three traits that form the so-called "triarchic model" of psychopathy). They also sequenced the AVPR1A regions of the chimps' genomes.

Latzman and his team decided to home in on this gene because it codes for a receptor for vasopressin, a neuropeptide known to play a role in complex social behaviours in humans and other animals, and so, in theory, relates to psychopathy. Vasopressin levels have been found to correlate with a history of aggression in people with various personality disorders. And polymorphisms (variations) in a region of the AVPR1A gene have been associated with variability in a number of traits relevant for psychopathy, including increased novelty-seeking and decreased avoidance of harm in people, and also to personality in chimps.

Some chimps, like some people, score highly on scales designed to evaluate psychopathic tendencies.

The team also considered each chimp's gender (as there are sex differences in the vasopressin system) and also, given extensive work finding that genes can interact with early life experience to influence behaviour, whether each animal had been reared by its own mother (119 had been) or, because of maternal neglect, or illness or injury, the chimp had been reared, for its own wellbeing, from a very early age by people (59 fell into this category).

For chimps reared by their own mothers, whether they had a common polymorphism in a key region of AVPR1A was correlated with their score on disinhibition. Variations in the AVPR1A gene also correlated with scores for boldness, and the animals' total psychopathy scores. But for chimps reared by people, there was no relationship between their AVPR1A genotype and their CHMP-Tri scores.

While the team didn't directly measure vasopressin levels, the results are consistent with the idea that genetically determined levels of vasopressin contribute to psychopathic tendencies, and  "provide additional compelling evidence that psychopathic tendencies are rooted in basic, evolutionarily-meaningful dispositions," the team writes. The results also, of course, show an important role for the environmental factor of rearing experience (perhaps roughly equivalent to parenting or foster care experiences for children).

It would be interesting to know more about the interaction between early care-giver experiences and the heritability of psychopathy. In another paper published this year by some of the authors of the current research and others, nursery-reared chimps scored significantly higher on the measure of disinhibition than those reared by their own mothers, though there was no relationship between rearing environment and either boldness or meanness. Might the higher disinhibition scores among the nursery-reared animals overwhelm, then, any effect of variations in AVPR1A (thus explaining why the gene was unrelated to psychopathic traits in nursery-reared chimps in the current research)? Or is something else going on?

The US National Institutes of Health has scaled back some studies involving chimpanzees. But Latzman and his colleagues argue that ethically sound and scientifically justifiable studies could (alongside studies of people) provide valuable insights into biological and behavioural processes relevant not just to psychopathy but to psychological illness more broadly.