A Nonhuman Primate Model of the Out of Africa Theory Utilizing Chinese- and Indian-Derived Rhesus Macaques (Macaca mulatta)
Evidence suggests that certain genotypic variants associated with novelty-seeking and aggressiveness, such as the 7-repeat dopamine D4 receptor variant (DRD4-7R), short (s) allele of the serotonin transporter (5-HTT), and the low-activity variant of the MAOa promoter (MAOa-L), are more prevalent in human groups that radiated out of Africa than human groups that remained in Africa. Rhesus macaques (Macaca mulatta), like humans, are a widespread species of primates that needed to adapt to different regional environments with one group, Indian-derived rhesus macaques, largely occupying predictable and resource-rich environments, while the other group, the Chinese-derived rhesus macaques, has come to occupy less predictable and resource-abundant environments. Rhesus macaques possess orthologues of these trait-related genes, making it possible to compare the frequency of genotypes associated with these traits between members of two strains. DNA was obtained from N=212 rhesus macaques (n=54 Chinese-derived, n=158 Indian-derived) and genotyped for DRD4 (n=98), 5-HTT (n=190), and MAOA (n=97). Analyses showed that Chinese-derived subjects exhibited higher frequencies of the DRD4-7R and 5-HTT-s-allele when compared to Indian-derived subjects. There were no strain differences in MAOA-L genotype groupings, but the Chinese-derived subjects exhibited a more frequent high-activity (MAOA-H-6R) allele when compared to the Indian-derived subjects. The results suggest that the Chinese-derived rhesus macaques possess a higher frequency of alleles associated with novelty-seeking, impulsivity, and aggressiveness compared to their Indian-derived peers and that those genotypically-mediated traits may have beneficial to both humans and rhesus macaques as they spread into novel and unfamiliar environments.