2 min read

A gene for celibacy?

Tyson is, unusually for him, completely wrong here. 

I’ll ignore the use of “gene” to mean “allele”, since that’s a plain-English abuse of notation as harmless as calling Pluto a planet. Put more precisely, he’s saying “if you have a genetic variant (allele) that substantially increases your tendency to celibacy, you didn’t inherit it” 

The first problem is a statistical one. It would be surprising if you inherited a ‘celibacy gene’, but it would also be surprising if you got it by de novo mutation.  A typical person has about 100 point mutations not inherited from their parents. Most of these will have no effect, and it’s very unlikely for any of them to have such a subtle effect that you’d be normal enough to follow Neil deGrasse Tyson on Twitter but would have a substantially reduced interest in sex.  But if we’re stipulating that you have a ‘celibacy gene’, we’re conditioning on one of the two having happened. 

From the point of view of reproductive fitness, a ‘celibacy gene’ is pretty much like a ‘gay gene’. As Jeremy Yoder (an evolutionary biologist and gay) writes, gay men average about 80% fewer children than straight men, and there is evidence of a genetic component and no shortage of potential explanations. Nothing inconceivable here, move on. 

But there are more dramatic examples than `celibacy genes’. There is a recessive ‘gene for not having children’ that is carried by about 1 in 25 people of northern European ancestry, and it’s one where the molecular mechanism is well understood and until recently the effect was almost 100%. People with two copies of the deletion in amino acid 508 of the CFTR gene are less likely to have children now (especially the men) and were much less likely to do so in past generations

Loss of function in CFTR gives you cystic fibrosis. Before modern medicine people with cystic fibrosis died as infants. Until the development of intracytoplasmic sperm injection, men with cystic fibrosis were almost always infertile. But if you have cystic fibrosis, you almost certainly inherited it.