With medicine and technology, it might seem like natural selection no longer acts on us. But it does. Just because we can treat diseases, change our environment, or survive previously dangerous conditions does not mean that the forces involved in our biological history have disappeared.
Evolving does not mean improving or necessarily transforming into another species: it means that the genetic variants of a population change frequency between generations. Some become more common, others recede. In fact, an advantage in one place may be irrelevant or detrimental in another. This can occur by natural selection, when certain heritable characteristics influence survival or reproduction, but also by mutations, migrations or chance.
An example is in some populations in the Himalayas, where hereditary adaptations have spread that allow them to live at high altitude, with less oxygen available. In the case of Tibetans, certain genetic variants favor a physiological response that helps them function in these conditions without producing an excessive increase in red blood cells.
Another is being able to digest adult milk without suffering from lactose intolerance. In certain regions, the ability to continue producing lactase after childhood became more common over thousands of years, related to the history of livestock farming and the consumption of dairy products.
And we’re not just talking about the past: a study of more than 785,000 people found signs of natural selection in modern humans. The researchers analyzed associations between DNA variants and reproductive success, one of the ways by which certain heritable characteristics can change in frequency in subsequent generations.
Today our habits, culture and environment also count: they modify the pressures we experience, they do not nullify the possibility of continuing to change. Medicine changes the rules, but it does not stop our evolution.
REFERENCES
Iain Mathieson, Felix R. Day, Nicola Barban et al. “Genome-wide analysis identifies genetic effects on reproductive success and ongoing natural selection at the FADS locus.” Nature Human BehaviorMarch 2, 2023.
Richard P. Evershed, George Davey Smith, Mélanie Roffet-Salque et al. “Dairy, diseases and the evolution of lactase persistence in Europe”. NatureJuly 27, 2022.
Emilia Huerta-Sánchez, Xin Jin, Asan, Zhuoma Bianba et al. “Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA”. NatureJuly 2, 2014.
