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Still Running Amok: Spree Killers

Research into recent tragic events in Plymouth, and what biology can offer.

Key points

  • There are two identified types of spree killers (both mostly male), one older and one younger.
  • The recent Plymouth spree killing fits an established pattern set out by behavioral ecology: Young, "spare" males are a danger.
  • Young men are prone to cultish-like stories of sexual separatism and entitlement.

I normally wait until papers have passed peer review before blogging about them, but, once again, tragic events have led people to ask questions about work we are doing on a paper that is still in preparation. And offering (partial) explanations for events such as the tragic killing of five innocent people, followed by the suicide of the perpetrator in Plymouth, is what you, the taxpayer, pay me to study.

If you follow this blog, you will know that a couple of years back, we published about spree killings—defined as the willful injuring of five or more persons, of whom three or more are killed in a single incident—using a United States database. Our reasons for picking that country were because the combination of reliable media data and free availability of firearms made comparative analysis far easier.

We avoided events with clear political or religious motives and found that, broadly, there were two types of (overwhelmingly male) spree killers. The younger type (average age 21) was more likely to have a history of mental illness, school refusal, no children or partner, and was (more or less) on the road to reproductive oblivion. The older type (average age 42) was not simply an older version of the younger ones. On the contrary—they had partners, children, and jobs but had either recently lost these or were in the process of doing so. Motivated more by an "If I can’t have them, no one can" style, they were also more likely to die in the course of their crime.

Many things were left to study. In the interim, we have been exploring the fans of spree killers and the pattern of spree killings in countries where guns—especially automatic weapons (1)—were less available or their use was less successful (from the perspective of the killer). It’s that latter study I want to talk about today. It turns out that across 43 cities in five continents where guns (especially large-capacity, rapid-fire weapons) are not easily obtained, the same patterns we observed in the U.S. were clearly seen. The only difference is that knives or vehicles are typically used instead, and they are not as effective at killing, so often, the incidents are not recorded as spree killings.

Can biology help us understand what is happening?

I look at human behavior through the lens of ecology—a lens that focuses attention on how organisms respond to (even recognize) threats and opportunities in their environment and have evolved systems to respond to these patterns. This approach tends to emphasize ultimate explanations (cashed out in terms of fitness) rather than proximate ones (that look at, say, conscious motives). Think of the differences as "why" compared to "how," and you will get a sense of the different questions that get asked by different disciplines.

David Ley has recently penned an excellent essay on Psychology Today, looking at the online communities that this perpetrator frequented and the increasingly disturbing and misogynistic beliefs that he came to accept (to his own family’s mounting horror, apparently). Nothing I say should be taken to run counter to Dr. Ley’s account. Rather, an ultimate explanation seeks to frame questions such as—how is it possible in the first place that males in our species could fall prey to such radicalization in beliefs?

Human nature is evolved nature: It does not come from nowhere.

Very briefly, asymmetries in minimum parental investment (Trivers, 1972), with (in humans) females being obligate investors, drive males to honestly signal (Zahavi, 1975) features that make them attractive mates. In humans, given the high dependency of human infants, and eusociality of childcare and viability (Hrdy, 2001), these male-displayed qualities include status, dominance, and formidability (the differences do not need to concern us at the moment) and in ways that peak at particular life stages (Stearns, 1976). The drives underlying these motives can go seriously awry—as when, for example, a man of 22 feels entitled to sex, sees other males (to him, sexually successful ones or "Chads") as his deadly rivals, and starts to adopt the language and belief systems of sexual separatism (see this post for details on aloof societies).

One thing has changed a bit in the interim. In our initial study, the younger spree killers were less likely to die in the course of their crime. This fits with a theoretical model that suggests that they are, at some level, attempting to prove their formidability to a skeptical world. However, that was not the finding in our recent study. The most interesting words in science are not "Told you so," but "Hmm, that’s interesting…."

What could be going on here? It took us a few years to publish that initial study (a story for another time), and, in the interim, there has been a rise of online groups of resentful males egging each other on. The younger type of spree killer now often leaves manifestos, statements of intent, and other material. They are now starting to leave records of their own understanding of why they do what they do.

Some have achieved levels of misogynistic hatred, coupled with desire (and resentment) that makes them a worrying combination. Some are showing levels of sexual repression (such as attempting to avoid masturbation) combined with resentment toward women, whom they believe are not giving them what they are entitled to. Hate admixed with desire is a very toxic brew, and the typical themes are sexual entitlement combined with deep misogyny. We know that young men are open to this sort of story—witness the recruiting power of the Taliban.

Is this a new subtype of the younger spree killer, more nihilistic even than before, and tapping into elements of human nature more akin to sexual separatism and cultish behavior? Watch this space.


1) Don't bother. No, seriously. I'm not interested in debating how many angels can dance on the head of an AR-15