Aggression in Primates
Aggression exists in species-specific combinations of these eight types. Jane Goodall (May 1979 also personal conversation) reported four different communities of chimps coexisting in Gombe, maintaining separate territories and harmonious relations.
But, chimps from Kasakela Valley suddenly began male-only forays into Kahama Valley. They moved silently, unusual for chimps. Over several months they singled out and killed lone males.4 When all the males of Kahama Valley had been killed, the breeding females were taken over and the territory appropriated.This is not that different from the situation among some hunter-gatherers. Napoleon Chagnon (1990) reported that Yanomamo men who have killed at least one other person have more than twice as many wives and children as those who have not, making “reproductive success” a cause at least of primitive war (Chapter 12). Joseph Manson of Michigan and Richard Wrangham of Harvard (1991) found that acquiring women was the direct cause of 45% of wars in a study of 87 hunter-gatherer societies, while acquiring resources to pay bride prices caused another 40%. This evidence supports Berndt and Berndt's (1951) view that “the majority of arguments in an aboriginal society are directly or indirectly brought about through trouble over women.”
Scientists who doubted that genes determine behavior responded somewhat sarcastically with a very logical challenge: which gene determines aggression (or any other specific behavior)? The human genome project, now complete, has found no such gene. However, psychologists, psychiatrists, and geneticists led by researchers such as Caspi (2003), Hamer (1998), Moffit (1993) and Zuckerman (2000, 2002, 2003) began to unlock the mechanisms. True, there are no genes for specific behaviors, but the brain is an electrical chemical organ strongly influenced by genes that affect the way it functions.
For example, a gene that lies on the X chromosome and makes the monoamine oxidase [MAOA] that breaks down dopamine and serotonin comes in two lengths. One produces low and the other produces high MAOA. Among maltreated boys, those with low MAOA are twice as likely to engage in bullying, fighting, theft, cruelty, or vandalism or be convicted of a crime as those with high MAOA. Absent abuse, low MAOA boys were no likelier to be antisocial than others.Apparently, genes can either exaggerate or moderate behavior. Genes are not switches that make a person aggressive, anxious, or shy. Rather, they determine brain chemistry and that in turn does affect personality. There is nothing simple about it (nor given the variety of human personality would we expect simplicity). At this point, geneticists suspect that a dozen genes together influence the tendency to take risks and court danger.
A logician would say the question of whether nature or nurture explains human aggressiveness might be a false dichotomy. A statistician would say that the two variables might interact. Biologists have recognized this since at least the 1960s, and are beginning to find mechanisms by which experience may modify genes. Such research is beginning to explain the well-known fact that most abused children become well-adjusted, law-abiding, and productive adults, but that a small number become abusive, violent, and criminal adults. If researchers such as Hamer are right, then it should be possible to identify families whose members take more chances than others do. On hearing the point, many think instantly of the Kennedy family. Joe Jr. earned the Navy Cross and DFC and was killed in the explosion of an experimental bomber during WW2. John was a decorated WW2 hero assassinated as was his brother Robert, and his son John died knowingly piloting a plane in weather conditions beyond his skill.
In people addicted to danger, when the dopamine rush from a particular thrill wears off, a greater one is sought. Children who graduate from thrill rides in amusement parks to risky driving to bungee jumping may be cases in point. Deborah Capaldi of the Oregon Social Learning Center argues that most problem children are thrill-seekers rather than aggressors. This suggests diverting thrill seekers from antisocial to socially useful behaviors such as smoke jumping, Special Forces, or venture capitalism.