Mankind’s declining intelligence?

A recent article in ScienceAlert, “Natural selection is causing a decline in human ‘education genes’, say scientists”.

Their case is dubious on several grounds, the main one being that of the half-dozen genes that make the largest contribution to intelligence, each one of them only influence about 1% to the individual’s total IQ test score. Other gene variations [mutations] which have some small effects — positive or negative — on inherited intelligence are scattered around our DNA in their hundreds.

At present, we very likely are a little less intelligent than our neolithic forebears of 10,000 years ago because an accumulating backlog of harmful recessive genes has built up and has caused a slight dilution of intelligence-related genes.

The only way this will be reversed is when couples intending to have children will have their fertilised eggs examined as a matter of course as they do now in IVF clinics. Any fertilised eggs that that contain a duplicate example of a harmful recessive gene — one from each parent — can be removed from the possibility of re-implantation in the mother.

Another way of dealing with this is by the recently developed technique of gene editing. In this case a potentially harmful recessive gene can be removed entirely and a ‘standard gene’ substituted before re-implantation of the egg in the mother.

Both of the above solutions will be a long-haul solution to the problem in the population as a whole — but then it was long-haul aggregation of harmful recessive genes that caused it in the first place.

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