An evo-devo model of bullying and juvenile delinquent behaviour

This article takes a life history theoretic (r/K selection) approach to bullying and juvenile delinquency, following evolutionary psychologist Marco Del Giudice Evolutionary Psychopathology (2018). Accordingly, bullying juvenile delinquency, as well as antisocial personality traits in general (callousness), are predicted by a fast life-history strategy that includes a bundle of traits like earlier sexual maturation, higher sociosexuality, higher risk-taking and less paternal investment.

While it is well known, that early puberty often comes with a host of antisocial behaviour, I will also argue that the risk for being the victim of bullying is associated with a slow-life history, thus explaining the common pattern that the bully is bodily much more advanced than the victim, who has typically more childish and neotenous traits.

Furthermore, my model goes beyond Del Giudice by providing evolutionary scenarios for different life-history strategies. I will argue that our ancestral modes of subsistence (foraging, farming, herding) had different life-history strategies.

There are many indications that for early farmers life was harder and probably shorter than those of hunter-gatherers, even though people in more modern agricultural societies live longer. It isn’t hard to see early farmers easily outbred hunter-gatherers due to higher fertility rates even though they might have had shorter lifespans.

However, there are also plenty of indications that pastoralists, who experience a lot of violence and instability, had the shortest lifespans. It is likely that evolution entrenched adaptive traits genetically, e.g. farmers with higher levels of serotonin (conscientiousness and future-oriented planning) were more successful. For pastoralists, whose lives were shorter, taking risks (dopamine) would have been advantageous for survival and mating. For hunter-gatherers, a childlike openness for learning in new environments and humbleness for a non-violent co-existence would have been the most advantageous personality traits.

Life history theory would predict the following traits for each evolutionary environment:

This pattern is very consistent and we can observe it in the Hadza (foragers) and their neighbouring Datoga (pastoralists). In the Hadza (monogamous, reproductive rate 4–5 years) fathers take an active role in child-rearing (alloparenting) and also see women as egalitarian partners. The Datoga (polygamous, reproductive rate every two years) hardly take part in child-rearing activities which they consider women’s work. The differences between the two tribes fit the pattern of r/K selection quite well.

What we can see here is an unpredicted correlation between caddism and dominance hierarchy. Whereas foragers like the Hadza are egalitarian (also towards women and children), pastoralist societies are hierarchically structured.

A man’s hormonal response to becoming a father depends heavily on his culture and the amount of time he interacts with his children. For example, dads in the Hadza foragers of Tanzania (who are generally socially monogamous) frequently hold, feed, and play with their babies, while dads in the neighboring Datoga pastoralists (who practice polygyny) are more likely to leave this to the moms and other caregivers. You can guess which dads have the lowest T levels — the Hadza. The T levels of the Hadza dads were found to be almost 50 percent lower than their childless fellows, while the T levels of the Datoga dads were no different from Datoga men without kids. (Carole Hooven, 2021)

Low paternal involvement or low parental involvement, in general, are known risk factors. Being abused or neglected as a child increases an individual’s risk for an arrest as a juvenile by 53 percent, increases the probability of arrest as an adult by 38 percent, and increases the probability of an arrest for a violent crime by 38 percent (source).

I have traced high-risk factors (evolved personality traits) to an ancestral environment of nomadic pastoralism and shown how the connected traits were highly adaptive in that environment. The picture we get by now is already fairly typical of known risk factors:

  • high in dominance behaviour
  • high impulsivity
  • high novelty-seeking behaviour
  • high risk-taking behaviour
  • high sociosexuality
  • low paternal (or parental) involvement
  • high in-groupishness (clan/gang formation)

How do these traits play out in development (ontogeny)? Even though high dominance behavior can be observed as early as kindergarten age, the most interesting age from and evolutionary point of view is puberty and adolescence. Bruce Ellis et al argue in “The evolutionary basis of risky adolescent behavior” (2009):

The current article articulates 5 key evolutionary insights into risky adolescent behavior: (a) The adolescent transition is an inflection point in development of social status and reproductive trajectories; (b) interventions need to address the adaptive functions of risky and aggressive behaviors like bullying; © risky adolescent behavior adaptively calibrates over development to match both harsh and unpredictable environmental conditions; (d) understanding evolved sex differences is critical for understanding the psychology of risky behavior; and (e) mismatches between current and past environments can dysregulate adolescent behavior, as demonstrated by age-segregated social groupings.

The authors base their model of risk factors on life-history theory and stress the importance of early sexual maturity:

Focusing on early adolescence makes a lot of sense, as this is the time when future life trajectories would be set by achieving high status, plus it’s the time when the mating market is maximally open, or as the authors put it: “The adolescent transition is an inflection point (i.e. a sensitive period for change) in developmental trajectories of status, resource control, mating success, and other fitness-relevant outcomes.”

Let’s see how this plays out in typical teenage bullying:

As we can see the early bloomer bully and the late bloomer victim often have opposite traits with the bully having pastoralist traits and the victim having a forager personality. What is striking is the obvious asymmetry. There is no way the fight between the bully and the victim can be fair and equal. This starts with more developed physical traits (muscle mass and physical prowess and a body that is biologically “older” in general) and ends with the social disadvantage: victims rarely have friends or “allies” to help them and few people would dare to challenge the bully’s behaviour as they tend to be popular or among the cool kids. If anybody stands up against the bully, it is most likely another hunter-gatherer type. Hunter-gatherers are quick to react to perceived injustices and start to bully the bully. This fact makes bullying with a lot of bystanders who do nothing about the bullying even worse for the bullied person because it feels like “he or she deserves it ‘’ and is perceived similarly to hunter-gatherer ostracism. Ostracism is very much the worst that can happen to a hunter-gatherer as it basically means death (hunter-gatherers rarely kill as a form of punishment).

What benefit does the bully have from bullying? The simple reason is to assert his position in the dominance hierarchy. By showing off his cruelty he signifies that others better not challenge his position. This kind of behaviour is frequently seen in animals with dominance hierarchies:

No matter the animal, testosterone’s relationship with aggression is clearly not one of simple cause and effect but instead is modulated by factors like previous experience, personality, and one’s position in a status hierarchy. In his book, The Trouble with Testosterone, the Stanford biology professor and expert on the endocrinology of aggression Robert Sapolsky illustrates this point with a description of an experiment in a captive group of Talapoin monkeys. The monkeys are introduced to each other and given time to form status hierarchies. When experimenters increase one of the monkeys’ T levels — “enough to grow antlers and a beard on every neuron in his brain” — he does do more chasing, grabbing, and biting. But what’s interesting is who is on the receiving end of his increased aggression: the T’d-up monkey is not indiscriminately harassing anyone who happens to irritate him. Instead, he beats up only on those beneath him on the totem pole and remains polite toward the higher-ups. (Carole Hooven, 2021)

There are many reasons why hunter-gatherer types are less popular and rarely have a network of allies to protect them. To begin with, many HG teens are socially awkward or even neurodiverse. It is well known that neurodiverse teens (ASD, ADHD and gifted) have low social intelligence and are frequently the victims of bullies. In fact, there are probably virtually no people on the spectrum who have never experienced bullying of some kind. Another factor may be evolutionary programming: while hunter-gatherer valued friendships, they do actively discourage the formation of alliances (something that comes naturally to pastoralist types). Alliances are a potential threat to hunter-gatherer egalitarianism.

The interesting thing about bullying is that both the bully and the victim have an elevated risk of becoming offenders

Frequent bullies and those who frequently both bullied and were bullied (8.8% of the sample) were responsible for 33.0% of all juvenile crimes during the 4-year study period. Frequent bully-only status predicted both occasional and repeated offending, whereas bully-victim status predicted repeated offending. Bullying predicted most types of crime (violence, property, drunk driving, and traffic offenses) when controlled with parental education level. However, frequent bullies or victims without a high level of psychiatric symptoms were not at an elevated risk for later criminality. (source)

This may seem contradictory to what I have proposed so far: forager types do have a low risk for criminality. A typical example of forager types are people on the autism spectrum. Such people tend to come into conflict with law enforcement because they tend to be “rebellious” and occasionally overreact violently, but the general incidence of crime among neurodiverse is rather low. An exception are people with ADHD who frequently abuse substances as a form of self-medication. In such cases the concerned people do get into trouble with law enforcement for illegal possession of drugs and related problems, such as theft.

Victims of bullying are otherwise much more likely to suffer from various mental health problems such as social anxiety and depression and to revert to self-harm and sucide rather than becoming perpetrators.

Most typical offenders will be found in the pastoralist group, whereas school shooters and some types of serial killers will be found more frequently in the forager group. Also, paraphilias, such as paedophilia, are more likely to occur in the forager group due to disturbed sexual development.

These two types have distinct and sometimes opposite life trajectories which may have similar outcomes at different stages of life, e.g. dropping out of high school or ending up in prison. The trajectory of the pastoralist type is characterized by social dominance orientation, i.e. trying to get higher up the social dominance ladders. The trajectory of the forager type is characterized by the egalitarian evolutionary programming, which may get the individual in conflict with his parents, peers, teachers, boss, etc.

Both appear to be antisocial. How is it possible to distinguish between them? The pastoralist type has a tendency to be exploitative, callous and proactively aggressive (Conduct Disorder/CD). It may be almost impossible to “tame” a pastoralist type child who is callous and who will shake off criticism and punishment easily. A forager type child is reactively aggressive (Oppositional Defiant Disorder/ODD) and may actually change due to reason and insight provided he or she is old enough. The pastoralist type child will try to form alliances with the “cool kids”, whereas the forager type child may be very much a loner or the outcast and will be much more likely to side with a bullied child than the “cool kids”.

Of course, ODD may develop into CD. This can often be observed in forager types at school where they will just start to misbehave in order to get some laughs from their schoolmates. However, this is more of a “there is no way out of this misery” strategy than innate callousness.

Apart from bullying, where it should be clear on which side each type is on, the types may end up in very similar circumstances, as mentioned above. Truancy, alcoholism, substance use, homelessness and juvenile delinquency are frequent outcomes for both of them. Forager and pastoralist genes may also be mixed in one person, of course, but in general, it should be easy to find out which type the forensic investigator is dealing with. There should be marked differences regarding:

  • Sexual activity
  • Gender attitudes
  • Sense of justice
  • Racism

There should also be other clues from development. Forager children are often highly reactive as infants, i.e. they cry easily, may have problems with falling asleep and sleep very little in general. They are likely to be reserved toddlers and children as well as highly sensitive (e.g. noise). They are also likely to throw more frequent and wilder tantrums than other toddlers. Such signs should be mostly absent from pastoralist type children.

Check out my book for more information on the evo-devo model:



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