A “new” study has apparently found that “children inherit their intelligence from their mother and not their father,” reports The Independent. Researchers have allegedly found that the intelligence genes are located on the X chromosome, of which the mother carries two, while men only have one. Not only that, but they also claim that those genes that are found on the single male X chromosome are turned off.
Despite no new study actually being reported on, it goes on to talk about how during development genes on the maternal X chromosome remain on, while those from the father are turned off. The turning on and off of genes is standard, as most of our pairs of 23 pairs of chromosomes actually contain the same genes, just different variants. This is partly a failsafe system, so that if you inherit a dodgy gene on one chromosome by accident, the chances are that the corresponding chromosome in the pair will have a healthy version to pick up the slack. Unfortunately, things are never as simple as they are often reported on.
As Forbes has already pointed out, there isn’t really much to go on here. We all have an X chromosome that we inherited from our mother, but the point is your mother had to inherit one of her X chromosomes from her father, as that’s how sex determination works (in humans at least). Not only that, but chromosomes are not set, unchanging entities, as they will frequently swap bits of DNA and genes between themselves in what is known as “chromosomal crossover” during the formation of sex cells. This allows for greater genetic diversity, and means that genes won’t necessarily stay on any one chromosome.
And to further complicate the story, while some studies suggest it is one of the most heritable of behavioral traits, there are other components thought to go into how intelligent someone is, with much of it still unknown. The heritability of intelligence, which is measured by the proportion of variation that can be attributed to genetics, is thought to peak at 0.75 in adults, meaning that for two individuals in the same environment, about 75 percent of the difference in intelligence between the two will be due to their genes. But as we all know, we are not all in exactly the same environment. Malnutrition and disease, for example, can play major roles.
As ever, things are never as simple as a headline may suggest. Even some of the seemingly simplest of characteristics, such as height, are controlled by a myriad of genes that we still don’t fully understand. Intelligence is vastly more complicated than this, so to boil it all down to a set of genes only located on the mother's X chromosome is hugely simplistic.