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 (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