Alcoholism

The book "Ghost Map" by Steven Johnson is about a terrible cholera outbreak in 1854 in London. Hundreds of people died in a very short period of time in a small neighborhood.  Cholera is an intestinal disease that is spread through unsanitary waste systems. It was an interesting book describing how the problem was solved. It was traced back to one water pump in the neighborhood. 

I love indoor plumbing.

Here is an especially fascinating detail in the book that really caught my attention.

The search for unpolluted drinking water is as old as civilization itself.  As soon as there were mass human settlements, waterborne diseases like dysentery became a crucial problem.  For much of history, the solution to this chronic public-health issue was not purifying the water supply.  It was to drink alcohol. In a community lacking pure water supplies, the closest thing to "pure" fluid was alcohol.  Whatever health risks were posed by beer (and later wine) in the early days, were more than offset by alcohol's antibacterial properties.  Dying of cirrhosis of the liver in your forties was better than dying of dysentery in your twenties.

Alcohol is a deadly poison and notoriously addictive.  To digest large quantities of it, your body needs to increase the production of certain enzyme called alcohol dehydrogenases.  Many living in rural areas lacked that ability, and were genetically unable to "hold their liquor."  Many of these died childless at an early age, either from alcohol abuse or from waterborne diseases.

Over generations, the gene pool became dominated by those who could drink beer on a regular basis.  Most of the world's population today is made up of descendants of those early beer drinkers, and we have largely inherited their genetic tolerance for alcohol.

The descendants of hunter-gatherers - like many Native Americans or Australian Aborigines - were never forced through this genetic bottleneck, and today they show higher rates of alcoholism than the general population.

This same genetic tolerance story is true of lactose, which went from a rare genetic trait to the mainstream among the descendants of the herders, thanks to the domestication of livestock.

Now you have heard something interesting.