Humans are still evolving, and alcohol may be helping to drive the process in some places. A variant of a gene that protects us against alcohol addiction, possibly by making boozing intolerable, seems to be favoured by evolution. So are several other gene variants.
Novel gene variants are known to have arisen and spread among humans in the recent past. One allows some people to tolerate the lactose in cow’s milk, so they can digest dairy produce. Other rapidly changing genes have been linked with education, smoking and Alzheimer’s disease.
People have been drinking alcohol , so it seems reasonable that our taste for booze – and the attendant dangers – could also have affected our genes.
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of the University of Pennsylvania and his colleagues have tried to identify regions of the human genome that have evolved over the last few thousand years. The group trawled through the genomes of about 2500 living people from 26 populations on four continents, obtained by the .
Really good genes
To pick out gene variants that are on their way to becoming established across humankind, the team looked for ones that have emerged relatively recently in seemingly disparate populations – such as in both westernmost Europe and easternmost Asia. The group assumed such variants are helpful, because they must either have spread rapidly across continents, or arisen independently and stuck several times over.
The team unveiled five genetic hotspots of recent change. One was centred on a gene called ADH, which is involved in metabolising alcohol. ADH makes an enzyme called alcohol dehydrogenase. This breaks down alcohol into acetaldehyde, a toxic substance that is then transformed into harmless acetate by another enzyme.
Several new variants of ADH have emerged independently in Asia and Africa in the last few tens of thousands of years. All of them seem to protect against alcoholism. It’s not clear how, but it may be that they break down alcohol so quickly that the toxic acetaldehyde accumulates in the body faster than the human body can clear it. A person who metabolised alcohol like this would feel unwell after even small amounts of booze, and would be unlikely to drink enough to develop alcoholism.
These protective gene variants may emerge in societies awash with alcohol, where heavy drinkers would die younger while abstainers survived to pass on their genes, says Voight.
But if that is the case, it isn’t clear why similar ADH variants aren’t equally prominent in Europe and the Americas. “It may be that we just didn’t detect it,” says Voight.
Changing DNA
The other four hotspots of genetic change relate to other things entirely. One that’s evolving in Africa and Asia is in an area that makes proteins called glycophorins, some variants of which are linked to protection against malaria.
And in Europe, genes that prevent the breakdown of homocysteine – an amino acid linked with heart problems – appear to be on the rise. So does a gene called DGKK, which is involved in correctly positioning the urethral opening on the penis.
Finally, two chunks of DNA inherited from Neanderthals also seem to provide an advantage: it’s not clear what, but one of these DNA regions is involved in testicle function.
“What this new study shows is that selection has also been tending to make some genes similar between populations,” says of the University of Wisconsin-Madison. The new traits “seem to help people adapt to recent changes in our ecologies”.
Source: Nature Ecology & Evolution, DOI: 10.1038/s41559-018-0478-6
