Soon after On The Origin of Species was published 150 years ago, a school of thought emerged that, owing to medicine and improved hygiene, natural selection in humans had stopped. Predictably enough, that was soon proved wrong. But what is emerging now is revealing: Our biological nature is not static; human intervention is changing it at a magnitude, and in a direction, that is unknown.
Until now, science has looked for selection signatures in human genomes. With technology, those signatures have come aplenty. In a forthcoming paper in Nature Reviews Genetics, evaluating data and evidence from several modern studies, scientists report that we are currently experiencing natural selection that is based on phenotypes or physical traits. What’s more, this selection can be measured, as it acts wherever there is variation in fitness and where that fitness is linked to genetic traits.
Large human studies show that in post-industrial society there is selection to reduce the age of first reproduction, to improve total blood cholesterol. It’s also apparent that selection for male height, a universally coveted trait, is more complex, with forces acting against both extremes—either being very tall or very short.
Globally, selection operates differently—humans in developed countries are more likely to vary in fertility whereas mortality rates play a greater role in fitness in developing countries.
Eye-opening as they are, looking at the wide-ranging evidence of natural selection among plants and animals, it can be said that we have just begun detecting the human traits that are under selection. What could be ahead is an imponderable scientific and philosophical question.
Science and society should look to estimate contemporary selection, using data from multi-generation clinical, demographic and epidemiological studies. That means we’d need data for a large number of individuals in a single population.
In some countries, personal identification numbers allow social, familial and biological information from various registers to be combined at the individual level. While no such registry exists in India, UIDAI, though still evolving, could aid in studying culture co-evolution.
Measuring how we are evolving, particularly through medical care and public health delivery, is crucial for understanding the long-term implication of recent medical innovations.
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