Mankind: Saved by Beer

You think I'm kidding?

To avoid dangerous water, people had to drink large quantities of, say, beer. But to digest that beer, individuals needed a genetic advantage that not everyone had -- what Johnson describes as the body's ability to respond to the intake of alcohol by increasing the production of particular enzymes called alcohol dehydrogenases. This ability is controlled by certain genes on chromosome four in human DNA, genes not evenly distributed to everyone. Those who lacked this trait could not, as the saying goes, "hold their liquor." So, many died early and childless, either of alcohol's toxicity or from waterborne diseases.

Thanks, George; I needed that.