Evidence of an Emerging Collision Between the Fertility Transition and Genotype-Dependent Fertility Differentials

In most industri alize nations, and in many developing countries as well, infant and child mortality rates have dropped precipitously while fertility is under increasingly active constraint, generating the so-called “fertility transition.” Within such a context, those genetic alleles that have been maintained in populations to compens ate for variation in disease vulnerability, and those alleles having relevance to sexual behavior, can be expected to experience increas ing selection pressure. Several examples of genotype-dependent fertility differenti als have been reported, prompting the present study. We examined the association between alleles at the dopamine D2 receptor gene (DRD2) TaqI site in a sample of 293 adult males from Catacamas, Honduras. Carriers of the A1 allele were found to have an earlier age at birth of their first child (p=.024) and increased total fertility (p=.007) relative to A1subjects. These data suggest that the 30% decline in fertility observed in Honduras during the past 25 years may be due to a disproportionate constraint on reproductive activity on the part of A1- males. Moreover, these findings also suggest that we should be able to expect that the DRD2 TaqI A1 allele will increase in prevalence in Honduras. These results, and those of other investigators, raise the possibility that changes in allelic frequencies, as an unexpected consequence of the fertility transition, may be playing a role in the observed increases in the prevalence of many so-called “diseases of modernization.”