Hominid ancestors beat humans to the drinks cabinet, say boffins

We're just aping our boozy ancestors

Here's a surprise: the ability to metabolise alcohol evolved long, long before humans became brewers, wine-makers or distillers – about 10 million years before.

In research published in PNAS (abstract here) in late November, a bunch of genetic detectives have worked backwards through the development of the enzymes that handle alcohol to come up with that startling number.

The paleogeneticists were looking at the alcohol dehydrogenase class IV (ADH4 to its friends), which is seen throughout the primate world, although not all primates can handle the sauce.

As explained by Science here, ADH4 takes the first step in breaking down alcohol, but primates like lemurs and baboons have a less-effective version than humans.

Santa Fe College biologist Matthew Carrigan and his colleagues took the ADH4 protein sequence from 19 modern primates, working backwards through time to see how they diverged over time. Their conclusion: “our ape ancestors gained a digestive dehydrogenase enzyme capable of metabolising ethanol near the time that they began using the forest floor” – about 10 million years ago.

Going back 50 million years, Science explains, the much more ancient forms of ADH4 could only handle small amounts of ethanol and broke them down very slowly, while a common ancestor of humans, chimps and gorillas have an ADH4 version that's 40 times more efficient.

That adaptation was important for the ground-dwelling apes, since it meant they could tolerate the fermenting yeast and ethanol present in fruit that had fallen from trees. Having better processing of ethanol makes it easier to tolerate the consumption; without the enzyme, Carrigan told Science, the ape would get drunk much more quickly.

And there's a serious point to all of this: it does some way to explaining why humans are vulnerable to alcoholism. Tolerance for ethanol would make apes with the efficient ADH4 able to get more food, which would lead to the brain developing pleasure pathways linked to alcohol consumption. ®