Biology Literature Review

Hope Hultgren

Biology Literature Review

McAuliffe, Kathleen. "If Modern Humans Are So Smart, Why Are Our Brains Shrinking?" Discover September 2010 Web. 6 Feb. 2009.

I chose this article because it speaks of an issue I was surprised to learn about, and because it is a matter that could affect me and everyone else. The article is about the astonishing fact that the human brain has apparently been shrinking since the Stone Age, hence suggesting we are getting dumber day by day. It touches on a myriad of theories as to what could be the reason for this. Some are convinced the deterioration of our gray matter signify that modern humans are in fact getting dumber. Others believe just the opposite. They conjecture that as the brain shrank, its wiring became more adept, turning us into faster, more clever thinkers. Still others hold that the decline in brain size is evidence that we have tamed ourselves, just as we domesticated cattle, sheep, and pigs, all of whom have smaller brains than their wild ancestors. The author does not seem to have his own theory or opinion on the subject, just states everyone else's. At the end he says that human brain size appears to be on the rise again, and concludes that perhaps our changing brain size is a mixed bag and that we cannot detect where evolution is taking us.

* Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion.

* No one really knows why this is happening.

* Encephalization quotient (EQ), the brain volume to body mass ratio, is the relevant metric here, not just brain size.

* David Geary of the University of Missouri suggests that humans are getting dumber, arguing that EQ has been varying inversely with population size. That greater population density requires less intelligence to survive.

* John Hawks of the University of Wisconsin suggests that humans are merely just getting the most efficient balance of brain size and energy use. He says this has been occurring because of an increase in population, so the likelihood of this optimization occurring increases.

* Richard Wrangham of Harvard suggests that the decrease in EQ is caused by self-domestication. He attributes this change to capital punishment and the process of exile, by which the most aggressive members of society are expelled from the gene pool.

* Brian Hare of Duke University agrees with Wrangham that humans are domesticated. He compares humans to bonobos, who are more cooperative versions of chimps and have 20% smaller brains.

* Recently (since colonial times), brain volume has been increasing. Richard Jantz of

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