A garbled post from a website called Second Nexus has gone viral in my feeds (and possibly yours), likely because of its eye-catching headline claim that “New Research Establishes That Intelligence Is Inherited From The Mother.” The piece is bylined “Editorial Staff,” presumably because everyone was too embarrassed to put a real name on it.
The premise of the post seems to be that science has traced “intelligence genes” to the X chromosome and that: children are more likely to inherit intelligence from their mothers because intelligence genes are located on the X chromosomes (and mothers have two).
Mothers do tend to have two X chromosomes, but they aren’t identical chromosomes, and of course, they got one of them from their fathers. Mothers generally pass only one X to their children (after the two X chromosomes engage a little genetic swapping themselves), and those children, in turn, receive the second sex chromosome (X or Y) from their fathers. Whatever is on the X can pass from mother to child or father to (usually) daughter, but the two X chromosomes the mother has aren’t the same and don’t at all automatically double the odds of inheriting a specific variant.
But there’s more. You may know that many people walk around with two of these huge chromosomes whereas others of us seem to function just fine with one. The doubled “gene dosage” for people with two (or more) X chromosomes is adjusted downward in a clever way: each cell turns off most of one X or the other. So inheriting an X-linked gene variant isn’t a guarantee that it will even be used because some cells might just shut it down.
And everyone has at least one X chromosome. Mother Nature, like Oprah, doles them out to her entire studio audience–i.e., all of us: And you get an X chromosome, and you get an X chromosome! And so do you!
Finally, when you inherit an X chromosome (which you have done if you are reading this), short of a major deletion, you’re getting whatever genes are on that chromosome, linked to intelligence or not. Of course, the Editorial Staff really are referencing gene variants that might be linked to intelligence, not just genes.
So let’s get this out of the way: Intelligence is complicated. While maybe half of our intelligence as we currently define and measure it is inherited, that proportion is in turn fractured into many many genetic variants scattered across our genomes. These variants operate together in various ways to form what we view as intelligence. And each of those fragments of heredity that contributes is itself subject to a host of environmental factors, both in its immediate molecular world and inputs to the whole organism, that will influence function. And that influence continues after birth as an ongoing mutual interplay of gene variants and environment. It’s layer upon layer upon layer of interacting pieces. So no. Not just your mother. Not just the X chromosome. Not even just genes.