Recent evolution of human intelligence and its implications in psychiatric disorders

Recent evolution of human intelligence and its implications in psychiatric disorders

Selective sweep from standing genetic variation is thought to be a primary mechanism underlying human adaptation. Here, we analyzed 15 ancient European genomes to identify >2,000 polymorphisms for which the derived alleles that have reached fixation in the present-day humans remained as standing variation 5,000~8,000 years ago. These recently fixed SNPs were significantly related to cognitive or neuropsychiatric disorders and genes involved in learning and memory as compared with the early fixed SNPs. The regions surrounding the recently fixed SNPs presented specifically high nucleotide diversity among the ancient humans, which was markedly reduced in the presentday population. The patterns of allelic diversity and fixation rates indicated that the derived alleles were maintained at a low frequency, most likely by balancing selection prior to undergoing selective sweep. Non-allelic diversity patterns suggested that interlocus gene conversion causing the homogenization of duplicate regulatory sequences was involved in some of the fixation events. The gene conversion signatures were frequently found at loci associated with neurodevelopmental or psychiatric disorders. Our findings demonstrate how palaeogenomic data can be used to discover novel evolutionary processes and suggest that some aspects of mental illness may be resulted from the recent evolution of cognitive function in humans.