Researchers have identified pervasive directional selection across West Eurasia, revealing that natural selection shaped modern human genomes far more aggressively than previous genetic models suggested. The findings, detailed in a series of studies including recent publications in Nature and Science, utilize ancient DNA to track allele frequency changes over 10,000 years, challenging the long-held belief that human evolution slowed down in recent millennia.
Hundreds of genetic shifts occurred in a short window
Geneticists leveraged an exponential growth in ancient DNA samples to measure changes over an 18,000-year period. They found hundreds of genetic shifts across Europe’s population within a relatively brief timeframe. This data suggests that the “signal” of evolution wasn’t missing; researchers simply lacked the sample sizes to see it.
One study identified 479 gene variants under natural selection in the West Eurasian dataset. Roughly 60% of these variants correspond to known traits in present-day populations, including a higher prevalence of red hair and a decrease in male-pattern baldness.
Diet and disease drove specific genomic adaptations
The transition from hunting and gathering to farming and pastoralism triggered significant metabolic adaptations. Analysis of more than 1,600 imputed ancient genomes shows that selection at the FADS cluster began earlier than previously reported. Similarly, selection near the LCT locus predates the emergence of the lactase persistence allele by thousands of years.
Pathogens also left a permanent mark. Strong selection appeared in the HLA region, which likely resulted from increased exposure to diseases during the Bronze Age. These adaptations to pathogens in post-Neolithic Europe may have increased the risk of inflammatory disorders in later populations.
Migration explains height differences more than selection
Not every physical trait is the result of natural selection. By analyzing over 400,000 samples from the UK Biobank, researchers distinguished between the effects of migration and selection. Height differences between Northern and Southern Europe are associated with differential Steppe ancestry rather than selective pressures.
Other risk alleles show distinct ancestral patterns. Risk alleles for mood-related phenotypes are enriched for Neolithic farmer ancestry. Conversely, risk alleles for Alzheimer’s disease and diabetes are more common in those with Western hunter-gatherer ancestry.
New tools allow for direct observation of allele changes
Ancient DNA provides time-series data that allows scientists to track allele frequency changes directly. This is a shift from previous methods that relied on comparing modern genomes to infer the past. The use of large reference panels and efficient phasing of low-coverage sequencing data has made this scale of analysis possible.
The Allen Ancient DNA Resource (AADR) now serves as a curated compendium of these genomes, enabling broader medical research into how ancient adaptations influence modern health.
What specific traits were influenced by this accelerated selection?
Evidence was found in 479 gene variants, with 60% corresponding to known traits in modern people, including a rise in red hair and a decrease in male-pattern baldness.
How did the shift to farming affect the genome?
The transition to farming and pastoralism led to selection signals related to metabolism, specifically at the FADS cluster and near the LCT locus.
