The genetics of marriage

Marriage is about procreation, as the Catholic Church carefully explains. We all have a eugenic interest in our children so it would not be too surprising that married couples might show some interesting genetic correlations. We already know about assortative mating for intelligence, but could there be more?

A recent study, 'Genomic Assortative Mating in Marriages in the United States' discusses

"genome-wide genotype data from the Framingham Heart Study (FHS; number of married couples = 989) and Health Retirement Survey (HRS; number of married couples = 3,474), this study investigates genomic assortative mating in human marriages."

The paper was published six months ago; their main result:

"Overall, our data suggest a degree of genomic assortative mating at the allelic level in married couples who were born in the first half of the 20th century in the United States. Apparently, this degree of genetic assortment averaged over the human genome is much smaller than the 0.20 Pearson had conjectured based on the observed correlations in height and arm span between husband and wife. As alluded earlier, certain genetic variants such as those underlying height are likely to be heavily assorted; however, the level of overall assortment in the genome seems much less.

However, a genomic correlation of 0.015–0.02 with married couples, estimated for the “positive” assorting SNPs in HRS, can represent an important genomic assortment for at least two reasons. A married-couple correlation may be compared with genetic relatedness among biological relatives. A genomic correlation of 0.015–0.02 is close to the average genomic correlation (0.0312) among second cousins (or the genomic correlation [0.0312] of an individual with his grandfather’s grandfather). While an individual passively and unselectively inherits half of his or her genes from each of the two parents, married individuals consciously or unconsciously assort on genes that play a strategic role in their reproductive marriages."

A genomic correlation  of 0.03125 = 1/32. According to Richard Dawkins,

"For relationships as distant as third cousin, 2 x (1/2)⁸ = 1/128, we are getting down near the baseline probability that a particular gene possessed by [an individual] will be shared by any random individual taken from the population."

Dawkins is referring to an ethnically-homogeneous population, as in the phrase 'old English stock'. The GWAS research above proposes that, on average, husbands and wives are more closely related by a factor of four than random members of the population. Assortative mating indeed.

Expect much more on this down the line.