Why do human beings kill each other?

February 28, 2008 | By | 5 Replies More

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 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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Category: Culture, Evolution, History, Psychology Cognition, Statistics

About the Author ()

Erich Vieth is an attorney focusing on consumer law litigation and appellate practice. He is also a working musician and a writer, having founded Dangerous Intersection in 2006. Erich lives in the Shaw Neighborhood of St. Louis, Missouri, where he lives half-time with his two extraordinary daughters.

Comments (5)

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  1. Dan Klarmann says:

    Let's not forget that recent studies of chimps in the wild show that they also commit wars, sometimes even eliminating a competing tribe with comparable atrocities as done by man.

    War (focused amok mob violence) is not solely a shame of Man.

  2. Lord Biron says:

    Its human nature.

    We simply kill to survive. Its one of the most basic traits of our eveolution.

    Perhaps someday we will evolve to a higher state and learn to supprese these traits, but doubtful.

    Remember Flight or Fight. Its our basic way.

    Killing can be justified, denounced, condemned, praised, generalized, but always is the same… killing.

  3. Vicki Baker says:

    Perhaps someday we will evolve to a higher state and learn to supprese these traits,

    God, I hope so. It's such a pain having to clean these bloodstains out of the carpet all the time.

  4. Erich Vieth says:

    Vicki: I read your comment with some concern. Please call me sometime. Don't visit. Just call.

  5. Vicki Baker says:

    Is that real concern, Erich or just concern trolling? I suspect the latter! 🙂

    Lord Biron's comment just tickled my funny bone, I guess. Perhaps I'm wrong in assuming that most of the people who comment here are not engaged in a daily life or death struggle for survival, but instead benefit a lot from cooperative networks. I wonder if how much we "know" about the efficacy of killing as a survival strategy comes from watching movies and tv shows, where violence is always the best and coolest answer to most problems? Since a lot of my genetic material comes from people who opted out of taking human life for personal or political reasons sometime in the 1500's, I guess I have a jaded view of the premise that killing is necessary for survival.

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