EVILICIOUS: Cruelty = Desire + Denial (15 page)

The second, common form of killing is infanticide, carried out by both parents and recently immigrated males. When parents engage in infanticide, it is often a response to the lack of resources required to rear young. To enable this response requires overriding those instincts that evolved to take care of young. The primatologist Dario Maestripieri suggests that this can occur under conditions of stress. Recall from the last section that heightened cortisol levels are often associated with stress, which typically results in animals backing down from an aggressive attack. But when cortisol levels rise and are sustained over long periods of time, heightened aggression often follows, turning parental care into parental violence. In these situations, parents may kill their infants. This is as true of the monkeys studied by Maestripieri as it is of humans living under conditions of extreme poverty and stress — in the developed world, the United States has the highest level of infanticide, and as one researcher suggests, this may be due to the fact that extreme poverty is in close proximity to extreme wealth, a contrast that makes it even more stressful for the poor. In contrast with parent-initiated infanticide, the situation for recently immigrated males is different. Here, there are no parenting instincts to get in the way, and a deep motivation to kill infants sired by other males. By killing these infants, not only does the newcomer obliterate the competition’s fitness, but effectively reboots the female’s sexual receptivity. This type of killing is more like predation.

Both predation and infanticide involve significant asymmetries in size or weaponry between attacker and victim, making the kill relatively cost-free. These two forms of lethal aggression stand in striking contrast with the third and far more infrequent form in which the attacker and victim are from the same species, both adults, and thus, comparable in size and weaponry. This kind of killing or
adulticide
only occurs in a small number of species, but the attacks are sufficiently frequent to count as part of the repertoire: ants, lions, wolves, chimpanzees and humans. The rarity of adulticide raises important questions about the evolutionary pressures that favored this upgrade to killing others, as well as the mechanisms that evolved to make it possible.

Battles among ant colonies are notorious for their organized attacks, designed to kill the enemy and minimize costs. What is distinctive about ant battles and the deaths that ensue is that they are coordinated, with success driven by group size. As the biologist Eldridge Adams has demonstrated, bigger groups are more likely to win, more likely to kill a higher number of their smaller opponents, and less likely to incur any fatalities. Despite the similarities between ant and human battles, two differences undermine the usefulness of this analogy for understanding the evolution of lethal aggression in humans: ants are only a very distant evolutionary cousin, subject to extremely different pressures of social life, and their cooperative efforts are largely among individuals who are virtual genetic clones. When humans go to battle, cooperation is largely among unrelated individuals who are complete strangers. Only chimpanzees commit adulticide in a somewhat similar fashion.

When chimpanzees go on a lethal raid, it is anything but impulsive. In fact, chimpanzee lethal attacks look more like predation than any other form of aggression. Things start with a gathering of individuals, usually all males, followed by a stealth approach toward the victim. With the victim in view, the attackers move in quickly. Once they catch the victim, the attack is brutal, accompanied by frenzied screams and hoots, focused on body parts that are necessary for moving, communicating and reproducing. Though no one has measured changes in brain chemistry in chimpanzees, chances are that the same processes arise as when lions kill gazelles: dopamine most likely rises during the hunt in anticipation of reward, followed by opioid increases following the reward of the kill.

Chimpanzee attackers commonly have a numerical advantage over their victims, a ratio of at least three to one. This power imbalance reduces the costs of the attack by making it almost impossible for the victim to retaliate. Proof of this cost-benefit analysis comes from the fact that the attacking party rarely incurs injuries, whereas the victims rarely escape alive. In a well documented case from Jane Goodall’s site in Gombe, Tanzania, one chimpanzee community gradually eliminated their competitors in the neighboring community without incurring any deaths or serious injuries. The benefit of these attacks is that the attacking community gains access to additional resources by weakening the competitive strength of their neighbors.

The suite of behaviors that accompanies coalitionary killing in chimpanzees has led several scientists, most notably Richard Wrangham, to argue that this form of lethal aggression in chimpanzees is an adaptation, with deep parallels to human warfare. Like human warfare, chimpanzee groups with numerical superiority typically outcompete those with fewer individuals. Like human warfare, chimpanzee attacks are deliberate and take time to unfold. Like human warfare, the benefit of lethal aggression in chimpanzees is that it weakens the power of a neighbor, thereby enabling those who win to gain access to valuable resources. Given the variation in access to resources, this is the kind of behavior that is subject to selection. On this view, we inherited the upgrade to version 1.5 lethal aggression from a chimpanzee-like ancestor.

The claim that our capacity for killing, especially in war, is an evolved adaptation, is anathema to many scholars in the humanities and social sciences. This response is triggered by the belief that biological explanations imply inevitability, and provide an excuse for the atrocities we create. For these scholars, war, and more generally, the high levels of killing observed among human populations, are recent, cultural concoctions, born out of human intelligence, the invention of projectile weapons, and high population density, to name a few. From this perspective, biology plays no meaningful role in our understanding of human violence. From this perspective, culture can either trigger war or turn it off completely, an idea developed by the science writer John Horgan in his 2011 book
The End of War
. From this perspective, killing in chimpanzees is nothing like killing in humans. These general attitudes echo the famous 1986 Seville Statement
⁴⁶
on violence in which a group of distinguished scientists, including the ethologist Robert Hinde, the geneticist John Paul Scott, and the paleoanthropologist Richard Leakey, sidelined biology with the following five statements:

1. “It is scientifically incorrect to say that we have inherited a tendency to make war from our animal ancestors.”
   
2. “It is scientifically incorrect to say that war or any other violent behaviour is genetically programmed into our human nature.”
   
3. “It is scientifically incorrect to say that in the course of human evolution there has been a selection for aggressive behaviour more than for other kinds of behaviour.”
   
4. “It is scientifically incorrect to say that humans have a ‘violent brain’.”
   
5. “It is scientifically incorrect to say that war is caused by ‘instinct’ or any single motivation.”
   

The Seville Statement ended with the conclusion that “Just as ‘wars begin in the minds of men’, peace also begins in our minds. The same species who invented war is capable of inventing peace. The responsibility lies with each of us.” In essence, understanding our biology will not contribute to understanding violence and war because we
invented
war as well as peace, woven out of nurture’s cloth and her infinite tapestry of cultural potential. These kinds of claims about the role of biology in human behavior are at best incoherent and at worst plain wrong. They are also dangerous because they imply a view of human nature that is infinitely plastic, unconstrained by both universal features of our biology, as well as individual differences that predispose some to extreme violence and others to extreme altruism. These points have been eloquently spelled out by the evolutionary psychologist Steven Pinker, most recently in his treatise on human violence
The Better Angels of Our Nature
.

What makes the Seville Statement and other claims like it incoherent is a set of false attributions to biologists about the role of biology in human behavior. It is important to get this right as it is directly relevant to our understanding of why we evolved the capacity for gratuitous cruelty. Statements 2-5 are accurate in that it
is
incorrect to say that war or violence are
genetically programmed
, subject to stronger selection
than other kinds of behaviour
, built into the brain as a
violent brain
, and based on
instinct
with a single, inevitable output. But serious biologist don’t believe statements like these. The biologist Peter Marler famously spoke of singing in birds as an
instinct to learn
, while Pinker described our capacity to speak as a
language instinct
, capturing the pioneering insights of the linguist Noam Chomsky. A bird’s instinct to learn does not mean that there is a one-to-one, inflexible mapping between genes or brain circuits and a specific type of song. All songbirds have the potential to acquire their species’ song, and in some birds, such as mockingbirds and parrots, this capacity extends to acquiring the sounds of other animals and even sounds made by inanimate objects. But if there is no input at all, or if the bird is deafened, the output is deficient in structure, unrecognizable as a species-specific song. The same holds for the language instinct. Instincts are biological biases that enable certain capacities, while limiting the range of potential variation. Our biology allows us, but not any other species, to acquire language. This same biology sets up constraints, due in part to what our brains can keep in memory, what our ears can hear, and what our larynx can produce. Like songbirds, the specific content of what we say, whether in French or Vietnamese, is determined by where we grow up and who we listen to.

If there is any intelligible sense of
genetically programmed
or
instinct
, whether for violence, language, sex, or mathematics, it is that our biology provides us with the capacity to acquire these domains of knowledge and expression. This doesn’t mean that violence, language, sex or mathematics are inevitable or fixed in their expression. There are thousands of languages, ways of having sex, and forms of mathematical expression. There are also thousands of ways of being violent, and equally, ways of counteracting such violence. But none of this takes away from the importance of biology, especially its role in constraining the form that these expressions take in different environmental settings. To think otherwise is just wrong.

The debate about version 1.5 of lethal aggression gains interest if we restrict the conversation to the similarities and differences between chimpanzee and human killing. Similarities often speak to our shared evolutionary history, and point to the pressures that favored this form of violence. Differences speak to both changes in our biology and the environments we confronted and created.

Those who argue that chimpanzee killing is nothing like human killing, especially in warfare, come from two different traditions. On the one hand are anthropologists such as Robert Sussman and Brian Ferguson who suggest that chimpanzee killing is infrequent, yields little benefit in terms of resources or competition, and is restricted to populations that are either artificially provisioned by humans or crowded in by us. They also suggest that the archaeological evidence for human warfare doesn’t really begin until about 12,000 years ago. As Ferguson notes “To argue that war is a result of some sort of innate predisposition to wage it requires that war be practiced throughout our prehistoric past.”
⁴⁷
This date, so Ferguson continues, is too recent to invoke natural selection as a cause, and leaves unexplained why there is no earlier evidence of massive killing if our last common ancestors had this capacity.

These criticisms either fly in the face of contradictory evidence, have little to do with the original ideas, or conflict with the logic of evolutionary theory. Concerning chimpanzee killing, the evidence comes from multiple sites in East and West Africa, including sites with no provisioning and no crowding from humans. Further, analyses by Wrangham and his colleagues show that humans living as hunter-gatherers or subsistence farmers on the continents of Africa and South America, engage in coalitionary killing, using stealthy raids and imbalances of power to minimize the costs and maximize the benefits. Looking at thirty-two different small scale societies, calculations of the yearly median death rates were between 164-595 per 100,000. Looking at nine chimpanzee communities spanning five populations in Tanzania, Uganda, and Ivory Coast, the rates were between 69-287 per 100,000. Chimpanzees fall well within the range of human hunter-gatherers and subsistence farmers. This evidence not only suggests similarities between chimpanzees and human societies living under conditions most like our ancestors, but also provides a resounding rejection of the view that chimpanzee killing is infrequent and of trivial importance. If the rates of killing are comparable, then either they are trivial for both species or trivial for neither. Given that both chimpanzees and human hunter-gatherers live in small groups, killing even a few individuals can have a dramatic effect on their capacity to defend resources. Killing in both species is non-trivial.

Another similarity between chimpanzees and small scale human societies comes from analyses of two extreme warring cultures, the Waorani of New Zealand and the Yanomamo of Venezuela. Though violence accounts for between 40-55% of all deaths in these two groups, attackers appeared immune to injury, with no more than 5% dying in battle, and often no deaths at all. Chimpanzee attackers are likewise immune to injury, due in large part to the strategic use of imbalances of power.

The parallels between chimpanzees and humans living in small scale societies supports the idea that similar pressures favored the
capacity
for coalitionary killing in both species. But this does not imply that these species should always kill in this way, contrary to what Ferguson and others wish to conclude. To say that a behavior or bit of anatomy is an adaptation, is to say that it was designed to solve problems in a particular environment. If the environment changes, it may or may not work or may work less efficiently. It is also possible that the behavior persists even after it is no longer adaptive; this represents some of the best evidence for the genetic basis of a behavior. A no-killing period in the archaeological record, as Ferguson points to, is interesting, but in no way undermines the logic of an adaptation. Such periods are
predicted
on evolutionary grounds.