In the January 31, 2008 edition of Nature, author Dan Jones reviews what evolution indicates about human killing humans. As with many human behaviors, the evolutionists divide on whether killing of other humans is an adaptation [1](a change in organisms that allows them to live more successfully in an environment) or a “byproduct of urges toward some other goal.” There are intriguing arguments for both sides.
Some have suggested that individual murder is more likely a byproduct, whereas organized violence (such as the type we see in wars) is more often an adaptation. What is the biological evidence pointing to something other than byproduct? A 1997 study found that “the average volume of the orbitofrontal cortex between men and women accounts for about half of the variation in antisocial behavior between the sexes.” Combine this with Jane Goodall’s observations of gang violence in chimpanzees, where “the adult males of one community systematically attacked and killed the males of another group over a period of years, with the victorious group eventually absorbing the remaining victims.”
It is incredibly hard to weed out the cultural factors from the biological, of course. Here’s something I found interesting. Interpersonal attacks leading to death have declined dramatically over the past few centuries.
After rising from an average of 32 homicides per 100,000 people per year in the 13th and 14th centuries to 41 in the 15th, the murder rate has steadily dropped in every subsequent century, 21.9, 11, 3.2, 2.6 and finally 1.4 in the 20th century.
Not that anyone is suggesting that human biological evolution could account for this decline in human killings. This period of eight centuries is much too short a time period for evolution to have had any meaningful effect. The decline might be due to social factors, including the development of professional police forces and improved medical treatments.
Jones distinguishes international wars from local violence.
In major international wars people do what they do mainly because it is their duty in the role they occupy; combatants in institutional wars do not fight primarily because they are aggressive.
Jones also points out the intriguing relationship between deaths within groups and deaths inter-group conflict:
Humans and small societies . . . die much less frequently from fights within their groups than from group battles. One possible explanation is that they simply fight less. For an increasing number of behavioral scientists . . . the human ability to generate and group amity often goes hand-in-hand with out group enmity. [Researchers from Korea have produced models in which] all terrorism and war co-evolved, promoting conflict between groups and greater harmony within them. It all falls into place when you see the evidence that early humans lived in small, competing groups,” says [Robert Hinde, a zoologist from the University of Cambridge, UK]. “Your group was more successful if you cooperated with its members but not with outsiders.”
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