Ancient DNA Reveals Parallel Human Evolution Driven by Rise of Farming

United Kingdom - 7dayes News Agency

Ancient DNA Reveals Parallel Human Evolution Driven by Rise of Farming

A new, expansive study leveraging thousands of ancient and modern human genomes has offered unprecedented insights into how our species has evolved over the past 10,000 years. The findings indicate that human populations in disparate geographical regions across the world underwent remarkably similar, and often identical, evolutionary trajectories following the global transition to agriculture. This research, providing our most comprehensive picture yet of post-Neolithic human evolution, offers compelling evidence that shared environmental and dietary pressures led to strikingly convergent genetic adaptations.

Led by Laura Colbran at the University of Pennsylvania, the research team demonstrated that 'some of the same traits and the same genes are under selection in different populations'. This phenomenon, known as convergent evolution, describes how organisms independently develop similar traits in response to analogous environmental pressures. In the context of human evolution, it suggests that the adoption of farming, which brought about drastic changes in diets, lifestyles, and disease exposure, imposed largely uniform evolutionary challenges across continents.

To reach these conclusions, the researchers analysed over 7,000 ancient and modern genomes, a significant expansion from previous studies that predominantly focused on Europe. The ancient genomes, mostly spanning the last 10,000 years, proved crucial. Colbran explained that 'Ancient DNA lets us look at genetic history live, as it were, whereas a lot of other methods tend to try and infer that'. By comparing these genomes, the team identified 31 signals of recent evolutionary selection, many of which were shared across diverse populations, reinforcing the notion of parallel evolution.

One striking example involves the FADS1 gene, which plays a role in fatty acid metabolism. Before the rise of agriculture, fewer than a quarter of humans possessed a genetic variant that boosts the expression of this gene. The FADS1 enzyme converts shorter fatty acids, common in plants, into longer ones, abundant in meat, suggesting it confers an advantage to individuals with more plant-based diets. Today, this FADS1-boosting variant is widespread, present in over three-quarters of people in Europe, Japan, and northern China. The findings indicate that the strength of selection for this variant has remained constant in Europe over the past 300 generations but has significantly increased in East Asia over the last 100 generations, reflecting regional differences in dietary pressures.

Another compelling instance concerns the enzyme alcohol dehydrogenase 1B (ADH1B), encoded by the ADH1B gene. It is well-documented that a variant of ADH1B, which rapidly converts alcohol into acetaldehyde, producing unpleasant symptoms such as facial flushing, has become prevalent in East Asia. This variant is thought to have been selected for because it discourages alcohol consumption. While this specific variant was absent in ancient Europeans, Colbran’s team still found evidence of strong selection involving the ADH1B enzyme in these populations too, suggesting different but parallel adaptations to alcohol processing or consumption.

Beyond individual genes, the research also explored complex traits influenced by multiple genetic variants, such as the waist-to-hip ratio. While an increased waist-hip ratio is often linked to higher fertility, the study uncovered evidence of stabilising selection that keeps the female waist-hip ratio within certain parameters. 'It is a really interesting one in that we do see stabilising selection,' Colbran noted, suggesting an optimal value for this trait that varies subtly across populations depending on specific contexts.

Experts have lauded the study, with Alexander Gusev at Harvard University describing it as 'an exciting study that includes a lot of ancient DNA that hasn’t been analysed before'. Gusev added, 'The authors find that variants under selection in one population are significantly enriched for being under selection in other populations,' confirming that this implies 'that selection is likely to be parallel across populations. This has been hypothesised but not shown before.' Yassine Souilmi at the University of Adelaide also highlighted that 'Their new method takes full advantage of the large amount of ancient DNA available now,' enabling the identification of previously unknown regions of the genome under selection.

According to Colbran, these results are merely the tip of the iceberg. As more genomes are sequenced, particularly those from non-European regions, even more evidence of recent human evolution will be uncovered, promising a deeper understanding of our shared genetic history.

7dayes News Agency