Primates first appeared about 55 million years ago. The world was a cruel, uncivilized, dangerous place and one had to mind oneself if they had any hopes of surviving. Mammals, such as primates, were territorial yet social animals; they lived with who they were familiar with and were not fond of outsiders. Outsiders meant less resources and sometimes less mates. To fend off outsiders, sharp canines would have to be bared (grrrr). By doing so, they were able to establish their dominance and keep competition for both resources and mates low. Reasoning with the outsider to leave and pose no threat to the community already there was not an option; but violence would surely do the trick. And so it came to be that ancient primates were some of the only mammals with a high rate of death among them (1.8%). Similarly, when the first prehistoric humans appeared about 7 million years ago, the rate of death among them due to lethal violence was 2%. This should not come as a surprise as humans ultimately evolved from primates which tend to come from a particularly violent mammalian clade.
Cladogram with darker lines representing the more violent species and the red triangle within Hominoidea representing humans.
One of the many interesting things that both humans and primates have in common is the MAOA gene (aka warrior gene). Monoamine oxidase A is an enzyme whose purpose is breaking down certain neurotransmitters involved in aggression, emotion, and cognition. A mutant variant of this gene (which produces little or no functional MAOA enzyme) may result in the individual expressing enhanced aggression. Scientists speculate that the gene emerged 25 million years ago, some 30 million years after the first primates emerged. And as it is found in both humans and primates, we can only conclude that it was likely a genetic adaptation that primates acquired and that was favored by natural selection as it was passed down all the way to the first humans some 18 million years later.
So, it's evident that we have genes in our DNA which can result in brutal and violent behavior. Violence was quite inevitable for the ancient primates as it was used for protection and what not. We, on the other hand, live in a modern society with sophisticated institutions and laws. Using lethal violence to solve mindless spats or otherwise is more often than not not used in our day and age. Yet it occasionally does come up. Are those that express it outliers in our society or are they simply showing us what human beings are made of (dum du da daaaaa!)?
MAOA Gene in Riverdale?!
Still, it is possible that Hobbes was incorrect and that we aren't an inherently violent species, after all. Even though lethal violence may be part of our evolutionary history, that doesn't necessarily mean that it is engraved in our DNA. Prehistoric people were known to have been violent as several excavation sites have revealed such as the one in Kenya known as Nataruk. This site depicts a massacre in which at least 27 people (men, women, and children) were brutally murdered. It's unlikely that the aggressors attacked for kicks and giggles but it is likely that they attacked those who they viewed as competitors for resources and living space. Thus, it may not have been a genetic component leading the aggressors to act this way but environmental pressures on survival.
The environment in which you grow up in can also affect the way you behave as an adult. Results from research conducted by NIJ (National Institute of Justice) revealed that "childhood abuse increased the risk of adulthood crime by promoting antisocial behavior during childhood and adolescence..." The environmental conditions that one lives in throughout ones life have a significant and in many cases detrimental effect on the way their brain functions. For example, through the use of MRI technology, doctors were able to identify changes in the brains of adults who had been victims of abuse or neglect in their childhood. The research depicted that adults who had been exposed to such strenuous conditions in their childhood had significant changes in certain brain regions (hippocampus, corpus callosum, cerebellum, and more) that deal with important functions such as balancing emotions and impulses. Furthermore, studies have shown that individuals who were abused or subjected to stressful conditions in their childhood and who have the mutant variant of the MAOA gene (double whammy) are more likely manipulate, exploit, violate the rights of others, and commit violent, criminal acts.
MAOA Variant + Childhood maltreatment study data
On the nurture side of the argument, all I've been talking about is how aggression and abuse in early childhood can lead people in the wrong direction as adults. But what about poverty? Greg Acs, VP at the Income and Benefits Policy Center of the Urban Institute explains that the reason certain groups are more prone to live in a state of poverty due to "historical, economic, social, and personal factors." These factors fuel the discrimination these groups must live with, the same discrimination that limits their work and advancement opportunities. Stress, such as the one people living in poverty experience, can have similar effects on a person's developing brain like abuse. Research has found that when a person lives in poverty, their brain's limbic system (which processes emotions and triggers emotional responses) constantly sends "fear and stress messages to the prefrontal cortex, which overloads its ability to solve problems, set goals, and complete tasks in the most efficient ways." This overworking of the limbic system and the overloading of the prefrontal cortex may be what is leading those living in poverty to act in irrational ways and commit unlawful acts. And while this can happen to anyone no matter their social class, those living in poverty live in a state of constant stress and pressure, have it much worse than the majority of the population.
