INTELLIGENCE IS PASSED FROM MOTHERS

For the general public, the question of whether genes contribute to a person’s intelligence is a matter of controversy. Among intelligence researchers, there is no doubt that variation in intelligence is partly attributable to genes. In fact, the purpose of the very first twin study, done back in 1924, was to study the contribution of genes to intelligence.

Today, researchers can predict how similar the IQ scores of people will be based on how similar their genes are. Such work has confirmed what twin studies have long shown: In adulthood, the majority of variation in intelligence is caused by genes. We now know about many genes that can be used to predict intelligence. Geneticists can determine which version of these genes someone has and, based on how many IQ-enhancing and IQ-deflating gene variants there are, assign a “polygenic score” (a score based on the effect of many genes) that correlates at about 0.3 with IQ scores, which is moderate by conventional standards. 

If ancient DNA is sufficiently well preserved, we can make similar comparisons between people who are alive today and people who lived thousands of years ago. This would be an interesting way to judge the extent to which the history of human progress may be the history of the biological evolution of intelligence. Of course, in some sense, everyone knows the two are related. However, many people think that important genetic changes to humans stopped around 100,000 years ago, the difference between now and then is negligible.

In fact, standard equations from population genetics suggest significant effects in five or ten generations. Sophisticated analysis can determine the relative ages of different genetic clusters in the modern human genome, and such studies have shown that ever since the Neolithic Revolution of approximately 10,000 years ago, the human genome has been changing 100 times faster than what normally occurred.