What is it about?
The reason why certain dopamine system genes are highly polymorphic in humans compared to other phylogenetically related species in unclear. One hypothesis is that evolutionary selective pressures may have driven variation of dopamine signaling genetics, which impacted migration behavior ~50,000 years ago. Certain dopamine receptor D4 (DRD4) polymorphisms are associated with low neuronal reactivity and increased exploratory behavior, novelty seeking, and risk taking. We propose that this rapid migration into new habitats selected for individuals with low reactivity to novel stressors. In this study we account for neutral genetic structure by modeling the nonindependence of neutral allele frequencies between human populations. We conclude there is an association between migratory distance and DRD4 polymorphisms associated with novelty seeking behavior (e.g. exon III 2R, 7R alleles) that cannot be accounted for by neutral genetic processes alone.
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Why is it important?
The genetic determinants of human behavior and phenotypic diversity are exceedingly complex. This research provides evidence for why one particular neural sub-system to subserve behavior might have undergone selective pressure. Dopamine neurotransmission is fundamental to human appetitive and reward-seeking behaviors, movement, cognition, and sociability. Numerous lines of evidence suggest that Homo sapiens evolved as a distinct species in Africa by 150,000 years ago and began major migrations out-of-Africa ∼50,000 year ago. By 20,000 years before the present, our species had effectively colonized the entire Old World, and by 12,000 BP H. sapiens had a global distribution. This study supports that higher frequencies of novelty seeking DRD4 polymorphisms are associated with population histories of migration.
Perspectives
Because the out-of-Africa migration proceeded though a process of serial colonization, significant and demographically shared population size bottlenecks have occurred throughout the history of human migration across the globe. Thus, observed associations of migratory distance and allelic frequencies may result simply from cumulative effects of genetic drift that skew allele frequencies more dramatically with increasing distance from Africa. Our study is the first to demonstrate that neutral genetic processes of drift and/or admixture, which produce statistical non- independence among population data points, cannot explain the association between higher frequencies of novelty-seeking alleles in DRD4 exon 3 and migration distance.
Monroe Butler
University of California San Francisco
Read the Original
This page is a summary of: Novelty-seeking DRD4 polymorphisms are associated with human migration distance out-of-Africa after controlling for neutral population gene structure, American Journal of Physical Anthropology, April 2011, Wiley,
DOI: 10.1002/ajpa.21507.
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