Is Human Intelligence Declining?

Gerald Crabtree, a geneticist from Stanford University, wrote that human intelligence may have peaked before our ancestors left Africa in his latest two journal articles. He postulates that because evolutionary pressure (i.e. natural selection) no longer favours intelligence,  the cumulative effect of genetic mutations over many generations has caused an overall decline in human intelligence and emotional fitness.

In an interview, he said that “there is a general feeling that evolution constantly improves us, but it only does that if there is selection applied”. Furthermore, he claims that humans have sustained “two or or more mutations harmful to our intellectual or emotional stability” out of approximately 2,000-5,000 genes related to intelligence, and that these genes act similar to links in a chain, which are significantly disruptive to the overall system if compromised. These claims have been refuted by other geneticists, such as Kevin Mitchell, the associate professor at the Smurfit Institute of Genetics at Trinity College Dublin, who says that Crabtree’s claims ignore the other genes that do not cause intellectual impairments or disabilities.

Mitchell continued by saying that although genetic mutations could potentially lower intelligence, “evolution has gone to a lot of trouble to craft your genome so it’s finely honed to do its job, and it doesn’t make sense that you would have all this random mutation in your brain cells. Also, you would have a very high rate of brain cancer.”

Other responses to Crabtree’s articles were much less professional, but I’ll let you read the article if you would like to read the criticism, or to learn more about the possible decline of human intelligence over the last millennium:  http://www.popsci.com/science/article/2012-11/are-people-getting-dumber-one-geneticist-thinks-so

-Jonathan Frydman

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One Response to Is Human Intelligence Declining?

  1. genegeek says:

    I agree with Steve Jones – where is the data? If you are interested in the original papers, let me know = have copy at my desk.

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