A reader of The Frozen Gene analyzes the effects of contraception, abortion, and childlessness on the Selective Turnover Coefficient, otherwise known as d, in order to determine if they alleviate the problem of the Frozen Genome or not.
Here’s the core finding. Childlessness has increased dramatically — from around 10% in the 1940s cohorts to over 28% in Japan today. But the correlation between childlessness and genetic load has decreased. The childlessness term (1−K) × r has actually gotten smaller in its purifying contribution, even as more women are childless.
The medieval European Marriage Pattern — with its high celibacy rate and moderate r — extracted more purifying value from childlessness than contemporary Japan does with 28% of women never having children.
The supplement doesn’t change Day’s headline number. Contemporary d_total is about 0.02–0.03, compared to d = 0.015. The difference is within the margin of error.
The value is conceptual. It answers the question that people naturally ask when they hear the Frozen Gene thesis: but aren’t all those childless people being selected out?
They’re not. Or rather, they’re being removed from the gene pool, but not because they carry worse genomes. They’re childless because housing is unaffordable, because the credential pipeline delays family formation past peak fertility, because the employment structure demands two incomes before a household can form, because they chose not to have children for personal reasons that have nothing to do with their DNA.
The removal is drift, not selection. The gene pool is losing genomes every generation, but it’s losing them at random with respect to quality. The sieve has holes so large that everything passes through — and the few genomes that are caught in the sieve are caught by economic architecture, not by biological fitness.
Read the whole thing. I see no reason to question his conclusions; they tend to support what I assumed would be the case, since d is essentially quantitative in nature, not qualitative.