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According to Austrian ethologist Konrad Lorenz (1903-1989), aggression is a necessary and inevitable aspect of human nature. Impulses to act aggressively build up in our bodies, like fluid filling a tank. Every now and then, before the tank becomes full and the fluid overflows, our aggressive impulses need to be released, preferably channeled into nonviolent competitive activities such as sports. Play tennis every morning and you'll be a nicer human being. Is this really true?
Human beings probably have killed more members of their own species than any other animal species on this planet, so it's undeniable that ours is a pretty aggressive species when compared to the rest of the animal kingdom. There are many animal societies in which aggression and violence are rare or nonexistent. Cows are relatively peaceful animals, as are sea turtles and the mountain gorillas we see in TV documentaries titled "Gentle Giants." At the other end of the spectrum there are animals like the spotted hyena, whose cubs to try to kill their littermates from the moment they are born. The newborn hyena cubs haven't even seen the world yet because their eyes are still closed, but they are already biting their siblings on the face. Hyena cubs are born with sharp canine teeth and are preprogrammed for murder. Human beings are somewhere in between cows and spotted hyenas, but a lot closer to the hyenas than to the cows. Why?
It all comes down to economics and the notion that aggression, much like anything else, has benefits and costs. Mother Nature knows how to spend her resources, and you find aggression in the animal kingdom only when the benefits are greater than the costs. In some animal species, aggression is rare because individuals wouldn't gain much from being aggressive, and therefore it's simply not worth it. In other species, it's rare because although individuals would gain something from it, they would have to pay a high price. When the benefits of aggression are high and the costs are low, then you see a lot of aggression in a species. But what are these benefits and costs of aggression, exactly?
Aggression is a manifestation of competition: the need or desire of two or more individuals for the same thing. The benefits of aggression involve obtaining what we want. Many animals compete over food, mates, or use of space. Let's take food as an example. Fighting over food may be worth the price in some circumstances but not in others, depending on the meal. A monkey can eat all the bananas on a tree if he or she attacks and chases all the other monkeys away from the tree. Here the benefits of aggression are potentially high because the winner takes all. But imagine a herd of cows grazing on a large pasture. A greedy cow who wants to eat a lot of grass might start fighting with every other cow in the herd, but what would be the point? There is grass everywhere and way too many other cows to fight. In this situation the greedy cow would be better off simply trying to eat as much as she can without worrying about what the other cows are doing. And that is what cows do, most of the time.
The main cost of aggression is the risk of injury to yourself or a family member during a fight. Is it worth fighting over food if there is a risk that you or a family member could be seriously injured or killed? While the benefits of aggression depend on what individuals fight about, the costs of aggression depend on how individuals fight. In animals with deadly weapons such as large and sharp teeth or claws, the costs of aggression may be higher than in animals without such weapons. Animals with large weapons need them for hunting their prey but are typically very careful about how they use them on members of their own species. Lions are formidable predators, but you don't hear much about adult lions killing other adult lions.
People tend to compete for resources that can be monopolized, where the winner keeps it all. Therefore, the benefits of aggression are potentially high. In addition, humans are not naturally equipped with dangerous weapons such as horns, claws, or sharp teeth. A person can insult or punch another person, at relatively low cost to himself or herself. When our hominid ancestors discovered that they could throw objects to hurt or kill others from a distance (that is, when they invented projectile weapons), they found a way of reducing the costs of aggression to themselves even further. Fighting from a distance is far less costly than direct physical combat and allows individuals to reap the benefits of aggression while minimizing its costs. People with firearms are more likely to kill other people because shooting someone carries far less risk of personal injury than attacking someone with bare hands or a knife. Opponents of gun control in the United States argue that guns don't kill people; rather, people kill people. The simple fact that the cost of killing people with a gun is lower than the cost of killing them without a gun explains why people with guns are more likely to kill than people without guns: it's the guns that make the difference.
So, humans are aggressive because for us aggression is a valuable tool that's generally available at a low price. Does this mean that Konrad Lorenz was right about human beings having instinctive impulses to act aggressively? I don't think so. Aggression is neither necessary nor inevitable, and there is no fluid filling up our tank. We are clearly biologically predisposed to be competitive with members of our species; how competitive we are depends, among other things, on how much testosterone we have in our bodies. Given the potential high benefits and low costs of aggression, Homo sapiens is a species with a high potential for aggression. Whether or not this potential is realized, that is, whether or not we compete in aggressive or nonaggressive ways, depends on the environment in which we find ourselves. To control and reduce the expression of aggression, we can alter its benefits and costs and make it less profitable. Reducing the benefits is accomplished by not rewarding violence and by teaching others through religious or moral indoctrination that nothing good comes out of violence. The costs of aggression and violence are increased through punishment. However, when these mechanisms for the control of aggression break down, such as during wartime or a natural disaster, aggression and violence typically flare up. When parents or teachers are not around, even children kill one another, as was aptly described by novelist William Golding in Lord of the Flies. All of a sudden, aggression is on sale and everybody wants to buy! (A different version of this blog appeared in my book Macachiavellian Intelligence: How Rhesus Macaques and Humans Have Conquered the World).
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