No phenotypic consequences of archaic hominin alleles in present-day humans
Advances in paleo-genetics allowed the identification of protein-coding changes arising on the lineage leading to Homo sapiens, by comparing genomes of present-day and archaic hominins. Experimental validation of the potential impact of such changes has so far been restricted to functional assays and model organisms. Large-scale biobanking now makes it possible to identify present-day carriers of archaic alleles and to directly assess phenotypic consequences in living adults. We queried exomes of half a million people in the UK Biobank at 37 genomic positions with supposedly fixed human-specific protein-coding changes. This yielded 103 carriers at 17 positions, with variable allele counts across ancestries. Contrasting carriers and non-carriers of an exemplary archaic allele in SSH2, we observed no deviation from the norm in a range of health, psychological, and cognitive traits. We also identified 62 archaic-allele carriers for a TKTL1 missense change, previously shown to have large effects on cortical neurogenesis in brain organoids and animal models. Carriers did not show differences in relevant anatomical brain measures, and a substantial proportion had college/university degrees. This work offers an empirical demonstration of how large-scale biobank investigations of living adults can transform our understanding of human evolution. The findings challenge the notion of fixed human-specific genomic changes, highlight that individual interrogation of relevant sites is unlikely to yield major insights into the emergence of complex human traits, and emphasise the importance of including diverse ancestries when investigating origins of our species.