Violence is everywhere. Turn on the TV, even during the daytime, and you can see Magnum PI and the A-Team kicking ass as you eat your lunch. Factor in streaming services and you can watch the latest ultra-violence, far more gruesome than the over-choreographed punch-ups found in 1980s reruns, 24/7. Go to the cinema and you’ll see that many blockbuster movies come with a heavy side-order of cracked heads and bloodshed. Perhaps the entertainment industry, with what seems like an obsession with extreme violence, might just be mirroring real life, at least if you can believe the headlines? However you choose to ‘consume’ it, the news is an endless churn of ever more sickening examples of human-on-human violence directed against women, men, children, disabled people, minorities, pensioners; indeed no sector of society seems safe against the onslaught. We punch, kick, bottle, club, stab and shoot, we injure, maim, torture and kill, and we do it for revenge, to rob, to hurt, in anger, premeditated or without any particular thought at all. All of that violence is before we factor in the horrors of war, where political motivations, religion, fear, greed and frankly who the hell knows what create death tolls so large they become the sort of horrifying statistics that magnitude and familiarity have rendered mundane. Assault, rape, bodily harm, manslaughter, murder, crimes against humanity and even genocide dominate the headlines, while millions pay to watch organised, rules-based violence in the many fighting sports that we have devised to vent fury and raise revenue. With all the violence that surrounds us, you might be forgiven for jumping to the obvious conclusion that mankind (and here it really is appropriate to say mankind) is an inherently violent species, genetically predetermined to bust heads and spread suffering wherever we go.
Before we dive too deeply into the darker side of human nature (and of course, nurture), let’s define our terms. More accurately, let’s let the World Health Organisation define them for us: violence is ‘the intentional use of physical force or power, threatened or actual, against oneself, another person, or against a group or community, that either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment or deprivation.’ You might think that this is rather obvious and that violence falls nicely into the ‘we know it when we see it’ camp, but the literature on human violence is littered with words with everyday meanings that have more nuance in a scientific context. Violence, for example, is seen as being different from aggression, which was defined back in the 1990s as behaviour ‘produced to cause physical harm or humiliation to another person who wishes to avoid it’. On the face of it, quite similar, but recent work has considerably refined this definition to include explicitly the notion of evolutionary advantage, framing aggression as behaviour ‘intended to increase one’s own dominance and, thus, reproductive success’, a definition that can include a great many behaviours we would not regard as ‘violence’. Aggressive behaviours, at least according to some commentators on the topic, can include standing up for one’s beliefs, being assertive, defending others in need, pursuing careers in law enforcement and the military, business and legal affairs, sports, politics and even scientific debate. Violence, then, is a subset of aggression.1 A further subset of aggression, and indeed a subset of violence, is lethal violence. Killing another human represents the extreme end of the human aggression spectrum, and because it is arguably the type of behaviour that is of most concern to twenty-first-century society it will be the focus of this chapter. The role of aggression and the assertion of dominance in everyday life can be clearly seen, from the often toxic political debates playing out currently to the rapacious nature of big business. If the tendency towards such behaviour is the result of evolution, and I think it would be hard to argue that natural selection and genetics won’t have played some part, then these behaviours fit just as snugly here. But it’s my chapter and I’m going to focus on lethal violence, and if you don’t like it we can have that ‘conversation’ outside…
Are we evolved to be violent?
Against a backdrop of apparently ubiquitous human violence, and a history that is literally ‘one bloody thing after another’, it is all too easy to piece together an evolutionary scenario that leads us to the inevitable conclusion that violence today is a mismatch between modern society and our evolutionary past. Such a scenario could run very much as follows (and yes there are plenty of potential problems here that we will get to shortly).
Violence is, at times, of great benefit to violent individuals, regardless of the species. Males that can out-compete other males by being stronger, by being more violent, will get increased access to females and therefore will get more offspring. Regardless of sex, a ‘no nonsense’ approach to sorting out competitors will give increased access to territory, food, water and other resources like nesting material. Violence can solve some pretty pressing problems.
We are a social species. Early (and indeed not so early) humans might have profited from being violent towards other groups, outcompeting them for resources and benefiting members of the winning group. Such groups are often family-based, providing a background of shared genetics. Violent individuals may also have gained from being better able to defend themselves personally from attack.
Violence could be a component of more complex behaviour, governed perhaps by testosterone levels, which might be linked with other potentially useful traits like ‘ruthlessness’ or ‘assertiveness’. These traits gained violent individuals further social advantages within their group. It is all too easy to think of scenarios where violence could be directed towards members of the group and towards even close kin, and that such violence could work out as an advantage, perhaps disposing of individuals seeking to take over your status. For homework, watch Game of Thrones, although be mindful of the idea that emotions like guilt have been proposed to have evolved to curtail such behaviour (Chapter 5).
Individuals that were violent could have gained status in social groups as a consequence of that violence (again, Game of Thrones will get you into the right way of thinking here), and thereby gained more offspring, as long as we assume that status equals sexual opportunity. And let’s be honest, that is often the case.
If there was a genetic basis to violent behaviour, then any advantage that translated into more offspring could lead to the evolution of violence as part of the complex suite of behaviours associated with social behaviour. Ergo, we evolved to be a violent species. A huge benefit in some past environments, this is a real mismatch in the modern world where, despite what Hollywood might have us believe, going around beating people up is pretty much always a big disadvantage.
The basic logic falls out nicely and resolves down to a simple idea. Violence was useful in the past and that led to the evolution of violence that doesn’t suit the modern world; bingo, we have our mismatch. Armchair evolution isn’t going to wash here, though, and to work out whether there is any real truth in this Just So story will take us to some difficult places. First, we need to answer the most basic question: are we actually a violent species or are we judging ourselves too harshly?
It would be lovely to be able to say that humans are not in fact a violent species; that the concentrating effect of 24-hour rolling news linked with a certain morbid fascination with gruesome details leads to the perception of violence in society being mismatched with the reality. Sadly, we cannot say this or indeed anything close to it. What we can say is that, compared to other mammals, we are exceedingly violent. Seven times more violent if we take lethal violence as our measure, and that does feel like a pretty good measure.
Before examining the damning evidence of our violent tendencies and how we arrive at a figure of ‘seven times more violent’, we need to consider violence in the round and from a zoological rather than sociological perspective. Violence within a species, conspecific violence, is not limited to humans as even a cursory examination of the animal world will confirm. Watch ants as they encounter ants from another colony; the workers (all female, by the way) can rapidly escalate from aggressive curiosity with their antennae to full-on biting and shoving, often resulting in decapitation, dismemberment and death. Take a look at some male blackbirds at the height of their breeding pomp if, despite some vocal singing to show where territories start and end, one bird decides to overstep the mark. The resulting tussles are aggressive and decisive although not, as far as I am aware, fatal. I once had a very pleasant evening sundowner disturbed by the sounds and sights of ferocious fighting between two adult male white rhinos having a very serious, and pretty violent, set-to. Take a look at a lion’s face or the flanks of an old male hippo and the scars they bear clearly tell the tale of conspecific violence. Violence between individuals within a species is so common within the animal kingdom because at some point animals are competing for resources that are in short supply. There may be all kinds of fancy displays that have evolved to keep violence in check, because even if you win you might get hurt, but when push comes literally to shove animals are more than ready to roll up their metaphorical sleeves and get stuck in.
I have often heard it said that humans are the only species capable of lethal conspecific (within a species) violence. This is incorrect and hopelessly, if rather endearingly, naive. Lethal conspecific violence can be found in many species and sometimes rather surprising ones, like that byword for harmonious cooperation, the honeybee. Honeybee queens emerge from special peanut-shell-shaped wax structures called queen cells in a beehive. If the colony is ready to swarm, then a newly emerged queen will inherit the hive once the old queen leaves with around a third of the honeybee workers. This is a very fine prize indeed but the worker bees like to spread their risk; perhaps a potential queen will die while metamorphosing from a larva to an adult? To reduce that risk, the workers rear more than one larva to be a queen, pumping the royal-destined grubs full of royal jelly after they hatch from fertilised eggs laid by the mother queen. The first queen to emerge typically finds the other yet-to-emerge queens and stings them to death through the wall of their queen cell. Her sting is adapted specifically for this purpose, being smooth like a dagger; she is an evolved killer of her own species. What is more, those victims are her sisters or half-sisters. Bumblebee workers, by the way, often kill their mother queen as the season starts to draw to a close, simultaneously committing matricide and regicide.
Conspecific killers abound in the animal kingdom. Lions are well known for killing their own kind when a new pride male takes over. Cubs are hungry mouths to feed and unrelated potential rivals when they become adults. Also, and a more important factor in the short term, females with cubs are not in oestrus, which limits the incoming male’s reproductive opportunities. Infanticide provides a simple solution to all of these problems and a tasty canapé as a side benefit. Infanticide is known in a range of other mammals from gerbils to langur monkeys and in birds including wrens and jacanas (or lilytrotters, from their habit of walking over waterlily pads). Some particularly fascinating examples of infanticide can be found in insects. Giant water-bug males take care of eggs, guarding them and keeping them from drying out. Without males and their attention the eggs won’t hatch and this behaviour makes males a valuable resource for females. If a female cannot find an egg-less male, then she stabs and kills the eggs of a brooding male. Facing a reproductively barren future, the male mates with the egg-stabbing female and takes her eggs to guard.
I could go on here, because there are very many examples to pick from, but the point is hopefully clear. Conspecific violence, even lethal violence, is not a uniquely human trait. What is unique is the way in which we’ve run with it. We’ve become the absolute masters of tearing lumps out of our own kind, an assertion that is backed up by a study published in 2016 examining ‘sources of mortality’ (causes of death) from 1,024 mammal species representing most of mammalian diversity.2 A wide range of animals including whales, bats, pangolins and antelopes were thrown into the mix, along with a good mix of primates and more than 600 human populations ranging from the Palaeolithic era to the present day. Such an analysis is far from straightforward; it relied on collating data from a huge number of studies and, in the case of the human element, from a mix of sources that included archaeological evidence. Maria Gomez and colleagues defined the level of lethal violence as ‘the probability of dying from intraspecific violence compared to all other causes’. They worked through the available evidence to calculate that probability as ‘the percentage, with respect to all documented sources of mortality, of total deaths due to conspecifics’. This definition comes replete with a grim list that includes infanticide, cannibalism, inter-group aggression and any other type of intraspecific killings in non-human mammals, as well as war, homicide, infanticide, execution and other kinds of intentional conspecific killing in humans. They then looked at this data in relation to the phylogeny of mammals, the evolutionary family tree that shows the relationships of each group to the other. This phylogenetic approach allowed them to make solid inferences about the evolution of violence across the mammals as a whole. It’s a neat and involved piece of work that made quite a splash when it was published in the world-leading science journal Nature in 2016.
Lethal conspecific violence was reported for a whacking 40 per cent of the mammal species in the study, and this is almost certain to be an underestimate because of a lack of data on a great many species. So, humans are very far from unusual in killing each other, and the evidence suggests that conspecific violence has evolved multiple times and has been an advantage in many different species and scenarios. They also found a firm connection between the level of violence and the degree of shared evolutionary history. This indicates that violence is more likely to evolve in certain groups, although they were also able to show that this has quite a degree of flexibility, leading to different patterns in some closely related groups. As ever, it’s complex. Social species and territorial species were found to be substantially more violent overall, lending yet more weight to our speculative evolutionary scenario since we are social and in the most part highly territorial. Overall, some groups of mammals like bats, whales and lagomorphs (rabbits, hares and an adorable little group of fluffy creatures called pikas) had a low level of lethal violence, whereas other groups, most notably the primates, had a high level.
The analysis of lethal violence across mammal groups and knowledge of their evolutionary relatedness allowed Gomez and colleagues to predict the proportion of human deaths that would be caused by violence inflicted by fellow humans. Their prediction was 2 per cent and this value was robust to all kinds of changes in the statistical models used to generate it. Interestingly, 2 per cent was also pretty much the proportion inferred for the evolutionary ancestor of all primates (2.3 per cent) and of apes (1.8 per cent), indicating that lethal conspecific violence was a more or less consistent feature of our evolutionary past. As the researchers put it, ‘These results suggest that lethal violence is deeply rooted in the primate lineage.’ Across all mammals the level was around 0.3 per cent, making us around seven times more lethally violent to our kind than the average mammal. So far, our speculative evolutionary scenario is bearing up remarkably well.
There is of course a problem with values predicted from a statistical model and any inferences made from such values: they are simply predictions from a model. For humans though, we can test these predictions against actual values, because we have historical records and archaeological evidence. It is a tricky task to control for different factors including the absence of evidence from lethal attacks on preserved bones, the influence of battles, the likelihood of preservation of bodies that have died by different means and so on. However, controlling for as many of these factors as possible led the researchers to conclude that the level of lethal violence in human prehistory did not differ from the level predicted by their phylogenetic approach; it still comes out at around 2 per cent.
There was a large variation in the level of lethal violence between different periods and that allows us to infer certain things about the role of different factors in the expression of violence. Perhaps the most interesting of these inferences for our mismatch hypothesis concerns population density. Increased population density is a common driver of increased conspecific violence in other mammals but it seems that is not the case for us. Living in centres of high populations is, conclude the researchers, ‘probably a consequence of successful pacification, rather than a cause of strife’. Modern life might actually be reducing our violent tendencies, which is a pattern that is seen in lethal violence across time both in the Gomez study and in other studies, although as we shall see this is disputed. Overall, the level of violence in prehistoric humans matches the phylogenetic expectation, and our ancestors were exactly as violent as our evolutionary heritage suggests.
A genetic basis for violence
The argument that we have evolved to be violent is holding up nicely, but if we are going to claim that ‘evolution did it’ then we need the smoking gun provided by genes; evolution, remember, is a genetic process. The convenient ‘gene found for [insert trait here]’ headline beloved of the media is rarely the case and there is no reason whatsoever for assuming that ‘violence’, a complex trait that must involve many different components, is influenced by a single gene. Also, and this cannot be stressed enough, violence isn’t caused by genes. Having certain genes might lead to a tendency for violence to be expressed more in some people and in certain environments, but it is the interplay between genes and environment that is important in translating DNA to GBH.3 And even then, violence can be controlled; you don’t have to lash out. This is an important caveat to bear in mind because in fact it turns out there really are genes (note the plural) that are associated with violence (feel free to ring the correlation/causality alarm bells).
Some really clinching evidence for the genetic basis of violence in animals generally is the fact that we can breed animals to be more aggressive. Artificial selection for different traits, and the subsequent heritability of those traits in offspring, shows definitively that those traits have a genetic basis but rarely tells us much more than that. We know too that in humans, violence tends to run in families, as the stark title of a paper published in 2011 with an unusually large sample size conclusively shows: ‘Violent crime runs in families: a total population study of 12.5 million individuals’.4 Despite very convincingly backing up the title, this study still doesn’t give us absolute clinching evidence for a genetic association, since families share physical and cultural environments. The fact that the study found differences in the likelihoods for different types of violent crimes (arson, for example, being especially likely to run in families) further underlines both the strong influence of environment and the fact that ‘violence’ is a complex multi-factorial phenomenon, complicating any hunt for genes.
Given the practical and philosophical need that we have to understand violence in the modern world, it is not surprising that considerable effort has been put into the topic and the scientific literature is well populated with both empirical papers searching for (and finding) genetic associations, and review and opinion pieces discussing their findings. Just recently, a study identified 40 genes related to aggressive behaviour and shared between mice and humans,5 with genes for different neurotransmitter metabolising enzymes potentially indicating ‘treatments’ for aggression; the motivation being that if we understand the biochemical basis for violence, then perhaps we can mitigate it biochemically through drugs and other therapies.
We are starting to drill down into the genetic mechanisms of violence, and we will undoubtedly get an ever more refined and nuanced understanding of human violence as time goes by. For our purposes though it is enough to show that violence does have some genetic basis. Indeed a review of a number of studies looking at the genetics of violence concluded that ‘approximately 50% of the variance in antisocial phenotypes is the result of genetic factors’.1 In other words, genetics explain around half of the variation that we can measure in antisocial behaviour of which violence is a component.
Violence in humans is usually considered from a psychological and biochemical perspective. From this perspective, aggression and violence results from a state of mind developed through hormones and the nervous system, triggered by sensory input and mediated by conscious and subconscious processing within the brain. This is an entirely logical way to approach the topic. We are often interested in the differences between different people’s tendencies to violence and we tend to associate them with emotional states like anger, temper and stress or with brain-related disorders like psychopathy. Studies of animals that engage in violence are far more likely to focus on the physical and behavioural attributes that facilitate violence and the ecological and social conditions that provoke it and that have contributed to its evolution. Ecologically, the Gomez study highlighted the role that sociality and territoriality play in the expression of lethal violence in mammals including humans, and the phylogenetic comparison of us with other animals turned out to be a useful one in disentangling some of the evolutionary features of violence. Other researchers have taken an even more ‘zoological’ approach, looking at how evolution may have shaped aspects of our bodies for violence.
Straight off the bat we can link physical attributes of humans to the ability to inflict harm on others, up to and including death. We are physically strong and fast and being bipedal leaves our arms free to swing around. Even an average person of average build with no particular training can generate enough power behind a fist to kill another person if the right spot is hit (remember our skulls are not especially heavily built in some places). We have vulnerabilities and weak spots: the groin, the stomach, the liver and the kidneys provide soft and painful targets, likewise the joints in our arms and legs are susceptible to debilitating strikes. A blow to the correct part of the neck, where the carotid artery sinuses are, can be an instant lights-out, while ‘one punch’ deaths are a not uncommon tragedy.6 Our other limbs are no less lethal. Bony feet and powerful legs allow for the sort of graceful kicks you might see in the movies or the much more effective kind of brutal stomping that you might see in real life. Even though our skulls have vulnerabilities (the back of the neck, the thinner parts around the temple), the thicker portions at the front allow for our head to be used as a weapon for delivering devastating headbutts. On top of all this we can plan and use tools very effectively, allowing us to make use of all kinds of things as weapons, from sticks and stones to the Jason Bourne favourite, the tightly rolled-up magazine.
Make no mistake, we are a very handy physical unit when it comes to violence; but can any of the attributes we have for violence realistically be said to have evolved ‘for’ violence, rather than violence being just a useful by-product? The general opinion is no, but that hasn’t stopped an interesting pocket of research developing that suggests that the ability to make a fist and punch someone without hurting yourself has been a driver in the evolution of the human hand. The history behind the idea is an amusing example of how scientific inspiration can hit. David Carrier, a comparative physiologist at the University of Utah, was arguing at a conference with other scientists about whether the sperm whale’s oddly bulging head had evolved for the purpose of ramming other males in order to compete for females. Frank Fish, a biologist specialising in the biomechanics of aquatic mammals, thought not, illustrating his point by waving his fist and saying (according to Carrier) ‘I can hit you in the face with this, but it did not evolve for that.’7 Carrier was inspired; what if the hand had evolved for fighting? Or more accurately, the human hand, in the process of becoming more delicate and dexterous allowing for greater manipulation and tool-use, may also have evolved to ball into a fist that can punch but provide some protection against bone breakage.
Carrier’s fist-balling hypothesis wasn’t his first foray into the physicality of human violence and evolution. Some of his earlier work suggested that the human male face may have evolved relatively robust cheeks, jaw and brow to withstand punches. It is fair to say that this ‘punch proof face’ idea was not universally well received. Evolutionary biologist David Nickle was especially outspoken about it, saying in an article in the Los Angeles Times, ‘What I find most objectionable is that this type of research does a disservice to the general public by supplying a very wrong understanding of human biology, and more generally, human evolution.’8 The reason for these harsh words is that Carrier, Nickle thinks, is telling evolutionary Just So stories. Nickle goes on to add that ‘I think Carrier and Morgan’s [Carrier’s co-author, United States physician Michael H. Morgan] argument is akin to arguing that human speech evolved so that humans could more effectively lie to each other.’ This argument is an example of what has become known as a ‘spandrel’ evolutionary argument. Spandrels are the almost triangular spaces that are generated when two arches meet in a building and they are often used for the placing of decorative plaques or paintings. Evolutionary biologists Stephen Jay Gould and Richard Lewontin used spandrels as an example of a useful characteristic (a handy space to put some artwork) that is in fact merely a by-product of the ‘evolution’ of another characteristic (supportive arches). ‘Spandrels’ has become shorthand for the evolutionary loose thinking that a seemingly adaptive characteristic ‘must’ have evolved through adaptation rather than simply being a by-product; your fleshy outer ears are great resting places for spectacles but this is not the reason for their peculiar shape.
Carrier tested the fist-hypothesis using nine male arms that he obtained through post-mortem body donor programmes. Fishing line attached to tendons allowed Carrier and his team to control the wrist, fingers and thumbs of the arms. Strain gauges and accelerometers allowed the team to measure the force of impact, and the effects on the delicate bones of the hand, caused by swinging the arm against a padded dumbbell. It’s a solid enough method but it must have looked rather macabre to anyone passing by.
Controlling the shape of the hand with the fishing lines in the style of a fleshy marionette, the impact and strain caused by a clenched fist, an unclenched fist (where the thumbs and fingers provide less protection) and an open hand revealed some interesting findings. A clenched fist, buttressed by the fingers and thumb in a way that is possible for humans thanks to our more dexterous hand, was able to deliver 55 per cent more force safely, without damaging the metacarpal bones, than an unclenched fist and can deliver twice the force of an open hand. Carrier concluded that the human hand and its ability to form a buttressed fist is an adaptation for fighting.
Once again Carrier found himself sharply criticised, with Frank Fish leading the charge both in the academic literature and in the press. Talking to the Los Angeles Times, Fish, who holds a black belt in taekwondo and so knows a thing or two about hitting people, pointed out that the human body has many parts that are useful for hitting people, like knees, elbows and feet, but no one is arguing that those evolved for fighting. In the scientific literature, Fish published a firm critique in the same journal that the research appeared, concluding that ‘The Homo sapiens hand may have some fighting advantages, but there is no reason to believe it is anything more than adventitious happenstance.’9 In other words, the ‘fighting fist’ is a spandrel. Others were more supportive of the idea. David Puts, a biological anthropologist at Pennsylvania State University, commented that ‘I don’t think that, by itself, it’s convincing, but the authors are building an increasingly convincing case’ while even Frank Fish conceded that ‘I think he’s moved the topic along.’ It will be interesting to see where Carrier and others take this idea in the future. A possibly fruitful direction will be to examine differences between men and women, because as pointed out by Richard Wrangham, a biological anthropologist from Harvard with an interest in the evolution of violence, we would predict differences given that our underlying scenario is about male competition and violence supporting increased mating opportunity with females.
Controlling our tendencies
The evidence very much points towards an evolutionary explanation for human violence, or at least towards the tendency or possibility of lethal violence to be expressed as part of our behavioural repertoire. As unsettling as this might be, it is worth stepping back and taking a broader perspective. We may all have the capacity for violence but most of us, most of the time, are not violent. We may think about violence, we may enjoy watching violence and we may wish violence upon others at moments of frustration or anger, but the reality is that very few of us actually visit violence of any kind on our fellow humans. Fewer of us still will ever kill another person in a deliberately violent act. Although the possibility exists, and we have the physical and mental abilities to carry it through, the vast majority of us are not killers. One explanation for this is that there are evolved, adaptive ‘aggression inhibition systems’ in the brain that prevent us from carrying out violence when the benefit is outweighed by the cost. When we are cut up in traffic for example we may feel rising anger and visualise beating the offender to a pulp but the risks of a hefty prison sentence, relationship breakdown and financial ruin, very real costs that we can calculate rapidly, might prevent us from acting out our revenge fantasies. In other words, we can exercise self-control and are not the helpless actors of our evolutionary script. Alternatively, if we or those close to us are at immediate and life-threatening risk then the cost–benefit seesaw might tip and even the mildest mannered individual might let rip and, in some circumstances, kill. Regardless of the precise mental mechanisms that control our violent tendencies, the evidence shows that most of us can. On the other hand, some people are very violent indeed and this mismatched pattern of violence in humans in the modern world warrants an explanation.
One explanation for extreme violence is simple variation. The genetics of violence, and the genetics that play a part in the mental structures that control our violent tendencies and thoughts, are complex and will differ between individuals. Whenever we have differences between people we inescapably have some people who end up at the extreme ends of the distribution. In this case, one end would be people that may be more violent than most and the other end are the peacemakers. It may be that by the mixing of genes to create offspring we sometimes bring together genetic combinations that result in very violent individuals, despite extreme violence not being adaptive in the modern world.
A focus on genetics, though important from an evolutionary viewpoint, is only part of the picture. We know that it is generally the case that the interaction between environment and genetics that leads to the expression of traits and violence is no exception. One model that accounts for this interaction, and which refines our initial evolutionary scenario, is the catalyst model, proposed by psychologist Christopher Ferguson. In this model humans have an evolved aggression inhibition system termed an impulse control device, likely in the frontal lobes of the brain. This is a component of ‘self-control’, the lack of which is a strong predictor of violent criminal behaviour. Self-control is, like violence, strongly influenced by genetics, which accounts for around 50 to 90 per cent of the variance that we can measure in self-control.1 So far so genetic, but in the catalyst model it is the family environment (itself conflated with genetics of course) that interacts with our genetics to determine whether we end up with a violent personality. Environmental stresses and strains act as catalysts to provoke potential behaviours that are then filtered through the impulse control device. It is the relative influence of the drive for aggression (environmental experience interacting with genetic tendency) and the drive to inhibit aggression (via impulse control) that determines whether the environmental catalyst will result in a violent outcome. Some have interpreted this to mean that the frequency of violent behaviours will likely increase during times of higher environmental stress, and this does not seem like a particularly big leap intellectually. In layman’s terms, if you put people under stress they are more likely to snap.
Given that our environment has changed dramatically over the course of our history and that we have very recently created a world with increasing levels of stress (Chapter 5) are we, as the headlines might have us believe, becoming more violent? It is a straightforward enough question; however, the answer is anything but. It is possible to find equally confident assertions that we are more violent than we were in the past,10,11 that we are less violent, that violent crime is increasing, decreasing or staying the same, or that homicide rates have gone up or down.12 Much depends on where you look, how you look, your definitions and your analytical approach. It would be nice to be on the side of American psychologist Steven Pinker, who posits in his 2011 book The Better Angels of Our Nature: Why Violence Has Declined that, as the title suggests, violence has decreased. His explanation focuses on the roles played by the emergence of nation-states with strong central governments, the development of stable and valuable trade networks and our ability to communicate, all of which increase our dependence on each other and reduce deaths due to violence. A central plank in that argument is provided by data that suggest fewer people in more ‘modern’ societies, relative to the society’s total population, die in wars and conflicts than among the sort of small groups of hunter-gatherers and pastoralists that were typical for most of our history.
Pinker’s positive viewpoint has not gone unchallenged. A team led by anthropologist Rahul Oka from the University of Notre Dame in Indiana, USA took a statistical approach to deaths in warfare over the course of human history and came to the conclusion that we are no more or less violent now than in the past. They reasoned that the number of people likely to be involved in warfare, a vital component of Pinker’s argument, doesn’t scale linearly with population. They assert, entirely correctly, that the proportion of the population engaged in military activities decreases as population increases. A band of 100 people might have 25 or even more people as a military force, for example, but a population of a million people would not have 250,000 ready and willing to serve in times of war. According to Oka and colleagues it is this simple scaling effect, and not increasing interdependence and the benefits of peace, that is the driver behind reduced proportional casualties of war as human societies become larger and more complex.
The role of the media in the modern environment
One of the environmental changes of recent years that is of great concern in our understanding and framing of violence in the modern world is the domination of violence on television, movies and gaming and its potential influence on children. We can add to this mix the recent rise of internet streaming sites like YouTube, where violent scenes, including real-life killings, executions and atrocities, are only a click away. It is important to be aware, if you are not already, that it is very easy indeed to find and view graphic scenes of beatings, shootings, beheadings and far worse online. This is not content hidden away on the ‘dark web’ but content that is freely accessible and searchable via Google and sometimes linked via mainstream news pages. The possibility of such ‘entertainments’ being a part of, and potentially a large part of, a child’s environment as they grow up is real, recent and worrying. Such worries, although often stirred up by the very media that help to portray violence, are not to be trivialised. If we accept some form of the catalyst model, as seems sensible, then we accept the evidence that exposure to violence (including family and ‘upbringing’ violence) is a predictor of violent behaviour. If we also accept that our environment plays at least some part in determining the outcome of the tug-of-war between inherent violent tendencies and our inbuilt impulse control, then we must take seriously the idea that being exposed to violence at a young age could shape our response to violence. If we are creating an entertainment environment and online and virtual worlds where depictions of violence are interacting with, and amplifying, our evolutionary tendencies to violence, then we find ourselves in an extremely recent, concerning and potentially lethal mismatch.
Surprisingly, given that the links between media violence and real-world violence are often portrayed in the media as being ‘controversial’, there is relatively little controversy at all in the scientific literature. In 2011, the International Society for Research on Aggression, a society of scholars and scientists engaged in the scientific study of violence and aggression, appointed a special commission to prepare a report on media violence.13 The links between media and violence are not likely to be straightforward and, like most of what we have discussed in this chapter, are a minefield of variation, conflated factors, correlations, causalities and more besides. As the report says:
Of course, watching a violent movie does not normally lead people to assault another person when they leave the cinema. Nor is it true that avid players of highly violent video games often end up as violent criminals. No respectable researchers in this area would make such claims. Rather, the issue is whether watching violent movies and shows or interactively engaging in violent games in a virtual world increases the odds that people may engage in aggressive behavior in a variety of forms, both in the short term and in the long term.
With those caveats out of the way the findings of that report are clear and concerning. The commission found that ‘After taking into consideration numerous characteristics of the child and the environment, including risk and protective factors, research clearly shows that media violence consumption increases the relative risk of aggression, defined as intentional harm to another person that could be verbal, relational, or physical.’ In other words, there is a strong evidence base from an array of studies to support the hypothesis that ‘monkey see, monkey do’. Mimicry, of course, is an excellent evolved ability found throughout the animal kingdom that allows individuals to pick up all kinds of life-giving skills; its co-option into developing violence in young people in a changed modern environment is yet another unfortunate evolutionary mismatch.
Cited in that report was the work of Albert Bandura who, along with others, carried out pioneering research in the early 1960s that examined children’s behaviour following exposure to violent images. That description sounds rather less ethical than the experiments actually were, although getting the study past an ethics committee these days might prove to be a struggle. In what have become known as the Bobo Doll experiments, Bandura and others showed some children film of an adult playing with an inflatable doll during which the adult hits the doll with a mallet, kicks the doll, sits on it and generally gives poor Bobo a pretty hard time. After the viewing, children were taken to a playroom that contained lots of toys and, crucially, a Bobo doll. The children who had seen the film of Bobo getting a good pasting didn’t just recreate the violence they saw; they came up with new ways to beat up Bobo, and they played more violently with other toys. Seeing aggressive behaviour then isn’t just a case of ‘monkey see, monkey do’; it is ‘monkey see, monkey inspired’. Witnessed violence isn’t just mimicked, it is enhanced and refined, seeming to unlock and release the violent potential within. Fast-forward 50 years to a time of immersive ultra-violent video games, 3D virtual reality and streaming violence 24/7, and suddenly poor Bobo getting smacked over the head with a mallet seems like the mark of a gentler, more innocent age.
In the short-term, exposure to media violence causes changes in our brains. Things that are experienced at the same time start to become linked through neural connections, like for example a warm loaf of bread and its distinctive smell. As the connection strengthens between these ‘nodes’ through multiple exposure, the activation of one node can lead to the partial activation of the other in a process called spreading activation. Connections between strongly linked things can develop rapidly and even in young children there are neural pathways between indicators of aggression (guns, shouting) and violence (fighting, hitting). The consequence of these connections, which are an evolved part of the way our brains function, is that if a person is exposed to a violent scene, the resulting activation spreads out to connected nodes and activates, or primes, them slightly. When nodes associated with behavioural tendencies are primed, it makes the behaviour more likely to be manifested. If you doubt the power of priming, then consider this: studies show that if someone is being insulted, then the mere sight of a gun can cause the insulted person to lose self-control and retaliate aggressively. The sight of a gun has a priming effect, the insults activate the aggressive behaviour node further and the thin veneer of docility provided by our impulse control disappears rapidly. Exposure to media violence has the power to prime a very wide variety of nodes.
In the long-term, exposure to violence may have more subtle and disturbing effects. Our lives are complex and to make sense of that complexity we develop what psychologists call schema or scripts. In certain scenarios, like visiting relatives, a complex diversity of emotions, concepts and sensations are activated together in the brain. Perhaps you are visiting your grandmother’s house and the journey there, the sight of the house, its distinctive smell, the feelings you get on seeing your grandmother and so on are activated and they themselves link to certain memories and to a specific mental ‘script’ that allows us to behave appropriately in that situation. The ability to link together appropriate emotions, sensations and memory, and to act accordingly, is a valuable skill for a social animal. What is important to bear in mind is that once these ‘scripts’, these integrated knowledge structures, are activated they are key determinants of how we behave and they can influence what we do outside of what we are aware of consciously.
The schemas and scripts that influence, modify and to a great extent control our behaviour are affected by our experiences. They are moulded by the world around us as we grow and develop. Parents, siblings and other family members usually form our primary nurturing environment but as we develop other influencers allow us to modify our scripts and learn new ones, such as the ‘being at school’ script. For the child growing up in the modern world the influencers have developed beyond parents, peers and schools to include the media. If being with parents and peers is sufficient for children to learn appropriate behavioural scripts for situations, then being ‘with’ media is no different. There is now no real doubt that children learn from what they see and experience on screens, and if what they see is violence then their developing neural networks will reflect that.
Media violence can write new scripts for us but it has other effects. Violent scenes can act as triggers for violent thoughts and feelings already stored in memory and, if activated sufficiently often enough, can influence behaviour. It is also suggested that repeated viewing of violence and activation of those nodes in the brain can make people more prone to interpreting ambiguous actions as deliberate provocation: the ‘did you spill my pint?’ scenario. Add to this the portrayals of violence as ‘fun’, the fact that violence is often rewarded or respected and the framing of violence as heroic, and then we have a potent mix indeed for influencing our behaviour. Video gaming merely exacerbates this effect, with the repetition of violent acts resulting in changes to the brain that make it more likely for people to behave aggressively in the real world; when gamers play violent games, aggressive attitudes and behaviours are more likely (but not inevitable) to cross over from pixel to playground.
Another concern over the portrayal of violence in modern media, and in this we can include the news and other ‘worthy’ media as well as more recreational viewing, is its potential for ‘desensitising’ us. We watch the same thing over and over again, then we are no longer as emotionally engaged with it and, through this exposure to repeated stimuli, we become desensitised, no longer responding in what we would previously have regarded as an appropriate way. Whether it is mass shootings, famine, war or disease this desensitisation is well known and relatively well characterised. Desensitisation is another example of evolutionary mismatch with the modern environment. It is actually commonplace and important in our lives; the reduction in cognitive, emotional, physiological and potentially behavioural responses to certain stimuli protects us and allows us to carry out tasks or be in situations that would otherwise be difficult or impossible. Such situations don’t have to be dramatic or violent; prior to becoming a parent, dealing with a bed full of diarrhoea and vomit would have elicited a highly emotional and possibly physiological reaction from me, but experience has led to a degree of desensitisation, allowing me to deal with such situations relatively calmly and effectively. Desensitisation also explains ‘donor fatigue’ and the diminished power of emotionally charged ‘poverty porn’ images to elicit money for charities.
The modern world is characterised to a great extent by the pervasiveness of electronic media. Violence, including real-world lethal violence, sadistic violence, rewarded violence, ‘heroic’ violence and violence that can be acted out by the viewer as a willing participant is ubiquitous and readily accessible. The connection between media portrayals of violence and subsequent aggressive behaviour in children is well established on foundations laid down in the early 1960s. With ever more sophisticated gaming and highly accessible media on devices that never leave our sides and that attract children like moths to a flame, this new environment is a very clear potential mismatch with our evolutionary history if we want to live in a less violent world. It is something that should concern us all, as the children that developed their mental scripts and aggression inhibition systems in the last decade or so become adults. In case we feel like playing the ever-popular ‘blaming the next generation’ game, there is also increasing evidence that adults are affected by watching violence, making them more aggressive, although only if they tend to have more aggressive personalities to begin with.15 This should make us doubly worried given what we know about the influence of violence on developing mental scripts in children. We should always remember though that violence on the media isn’t the cause of violence; we were the most lethally violent mammal long before TV was invented.
Reducing violence
Discussing violence from an evolutionary perspective can attract criticism, in part because it is all too easy to think that an evolutionary argument ‘for’ a trait in some ways justifies that trait. This is an understandable reaction, but developing an evidenced idea that violence is in some way a part of our evolutionary heritage in no way excuses violence. We can develop, and indeed have developed, an equally powerful evolutionary argument for impulse control and the reduction of violence; it is this side of the complex balancing act that wins through most of the time in most of us. Understanding the evolutionary origins and significance of violence, and understanding the environmental triggers that provoke violence, actually gives us powerful insights and opportunities to understand and deal with violence. As Christopher Ferguson argues in a paper with Kevin Beaver entitled ‘Natural born killers: the genetic origins of extreme violence’:
From behavioral genetics and evolutionary models of violence, we may more fully understand which individuals are at greatest risk for extreme violence. We can then begin to examine the interaction not only between genes and environmental catalysts for violence, but also the interaction between genes and treatments and prevention efforts for violence.
The hope is that an evolutionary understanding might lead to more effective interventions to reduce violence, and that can only be a good thing.