Serial Killers
Serial Killers and the Inner Dinosaur
Biological perspectives on forensic psychology as it relates to serial killers
Posted February 3, 2025 Reviewed by Davia Sills
Key points
- Aspects of the "Triune Brain" theory have been largely discredited.
- However, understanding brain evolution may prove very useful in some areas of forensic psychology.
- Such considerations may help people to understand the cognitive and motivational factors in serial killings.
Serial killers hold a strange fascination for many people. The reason for this is difficult to ascertain, but why anyone would become a serial killer in the first place is even more difficult to understand. Granted, there is typically a sexual component to the phenomenon, as well as a variety of nasty idiosyncrasies, ranging from cannibalism to the retention of human body parts, that characterize many serial killers (e.g., Sharps, 2024). It’s also true that some serial killers, such as Ed Gein, have been judged to have had mental illnesses that might very well have impaired their judgment and decision powers.
However, for those in possession of at least reasonable cognitive capability, it’s extremely strange that anyone would dare to be a serial killer, at least on a continued and regular basis. Between the bits and pieces of victims that a serial killer tends to keep around the house, to say nothing of the horrendous smell that would result from human butchery, it’s pretty obvious that the average serial killer is ultimately going to be caught. And what happens next, once apprehended and convicted of horrible crimes, is obviously not going to be in the serial killer’s best interest.
Therefore, you would expect serial killers, no matter how much they might enjoy their murderous careers, to ultimately decide that the danger of continuing those careers is too great. They should simply stop doing it.
So why is it that a lot of them don’t?
Paul MacLean (e.g., 1973) set forth a theory of the “Triune Brain,” a theory largely discredited and even vilified today (e.g., Steffen et al., 2022). The basic concept was that the human brain incorporates an older mammalian brain, the limbic system, and an even older reptilian complex, largely represented in the basal ganglia, as well as the most recently evolved neocortex. The theory is justly criticized; it seems to imply less interconnectivity between relevant brain structures than is, in fact, the case. It is also misleading from an evolutionary standpoint; for example, modern research indicates that many reptilian and mammalian structures derive from common ancestry rather than from direct descent.
However, it is also true that many of our basic brain structures dealing with sex, aggression, and other behaviors of significant importance to the forensic realm (and to the behavior of serial killers) are shared at least analogously with modern reptiles and even with evolutionarily unrelated dinosaurs. For example, if you examine the fossil brain of a Tyrannosaurus rex, a cranial core endocast of which I have on my desk at this moment, it is difficult not to see a rather direct analogous comparison of the same structures in modern reptiles, and even in the subcortical reaches of the human brain as well.
So what?
I recall my collaborative student research under Professor David Chiszar on Russell’s Viper (Carr et al., 1982), a reptile famous for its spectacularly effective venom and for biting the living hell out of practically anybody it can reach. I could tell that the snake didn’t like me. I don’t think it liked anybody, but it didn’t appear to hate anybody, either. It just ate mice in a subjectively machine-like manner. It showed no signs of conscience or moral reasoning. It just bit things and sometimes ate them. That was pretty much it.
Reptiles have a fine grasp of the elementals, of course. Some things they bite, some things they eat. Sometimes they fight, sometimes they mate, and they can also signal aggressive and/or sexual intention, sometimes by hissing or by vocalizing some version of “Raargh!” That’s pretty much it.
Reptilian conscience is not in evidence, and it’s a good bet you could have said the same thing about Tyrannosaurs. On my desk, I also have a cast of a Tyrannosaur tooth. That single tooth is larger than the core of his brain. This creature was not much of a thinker, any more than was our Russell’s Viper, and given the very rudimentary cortical development found in ancient dinosaurs and in modern reptiles, we wouldn’t expect much in the way of moral reasoning anyway. It was pretty much “Raargh!” on a daily basis for the dinosaurs for over 160 million years. In our current world, all you get out of a modern snake is an occasional aggravated hiss, with lizards and crocodilians lying somewhere on the hiss-to-Raargh continuum.
Now, how might this be relevant to our consideration of serial killers?
The weaknesses of the Triune Brain theory notwithstanding, we have analogous Raargh-type subcortical structures embedded deep in our own heads as well, but most of us don’t go around killing or biting everybody because the impulses these structures may generate are typically opposed by the activity of our human neocortex. But many violent individuals, including at least some serial killers, have less neocortical gray matter than normal (e.g., Turner et al., 2020). Also, the connectivity between anatomically higher brain centers and subcortical structures, connectivity that may normally inhibit murderous human shenanigans, may be diminished in the more violent. Therefore, at least some serial killers and other murderous individuals may lack the relevant neocortical inhibitory powers to suppress the sex-and-violence impulses of what we might call their “inner dinosaurs,” and just as it might prove difficult to stop a Tyrannosaur from chowing down on a Triceratops or something, it might be similarly difficult for many serial killers to inhibit their nastier sex-and-violence impulses.
Obviously, this does not suggest a naïve return to the incomplete and oversimplified Triune Brain theory as such. However, given the analogous brain structures that humans have shared with many other species over evolutionary time, we might at least find some utility in the comparative examination of relevant structures and functions in the context of the brain’s evolution, with special reference to some of the extreme behaviors which occupy the forensic psychologist. Such considerations must, of course, be treated with appropriate scientific caution, but they may give rise to important hypotheses for understanding behaviors of significant forensic relevance.
References
Carr, J., Maxion, R., Sharps, M.J., Weiss, D., O'Connell, B., & Chiszar, D. (1982). Predatory behavior in a congenitally alingual Russell's viper (Vipera russelli). 1. Strike induced chemosensory behavior. Bulletin of the Maryland Herpetological Society, 18, 196-204.
MacLean, P. (1973). A Triune Concept of the Brain and Behavior. Toronto: University of Toronto Press.
Sharps, M.J. (2024). The Forensic View: Investigative Psychology, Law Enforcement, Space Aliens, Exploration, and the Nature of Madness. Amazon.
Steffen, P.R., Hedges, D., & Matheson, R. (2022). The brain is adaptive not triune: How the brain responses to threat, challenge, and change. Frontiers in Psychiatry, 13, DOI: 10.3389/fpsyt.2022.802606
Turner, A.S., Anderson, N.E., Widdows, M., Nyalakanti, P., Harenski, K., Harenski, C., Koenigs, M., Decety, J., & Kiehl, K.A. (2020). Aberrant brain gray matter in murderers. Brain Imaging Behavior, 14, 2050-2061.