Got Milk?

From 5000 BC, early Polish farmers had used pottery with perforations as sieves to separate fatty milk solids (curd) from liquid (whey). (Curd is a dairy product obtained by curdling (coagulating) milk with rennet or an edible acidic substance such as lemon juice or vinegar and then draining off the liquid portion called whey.) That makes the Polish relics the oldest known evidence of cheese-making in the world.

A project has emerged that probes the history of the development of milk use. The results are fascinating.

Historically milk was tolerated only by children. Children almost universally produce lactase and can digest the lactose in their mother's milk. But as the child matures, he loses this ability and can not produce the lactase enzyme to break down lactose, milk's main sugar. Even now, only 35% of the human population beyond the age of about seven or eight can digest lactose. Historically no adults could.  

But as farming started to replace hunting and gathering in the Middle East at the end of the Ice Age around 11,000 years ago, cattle herders learned how to reduce lactose in dairy products to tolerable levels by fermenting milk to make cheese or yogurt. The lactose--and the protein--is in the whey. But over the years a genetic mutation emerged in Europe that gave people the ability to produce lactase — and drink milk — throughout their lives. It appears the mutation  emerged about 7,500 years ago in the broad, fertile plains of Hungary. And those with the mutation survived more easily--and reproduced more--because they had a larger, tolerable food source. In a 2004 study, researchers estimated that people with the mutation would have produced up to 19% more fertile offspring than those who lacked it. The researchers called that degree of selection “among the strongest yet seen for any gene in the genome”.

But only if “the population has a supply of fresh milk and is dairying. It's gene–culture co-evolution. They feed off of each other,” says Mark Thomas, a population geneticist at University College London.

This led to another question, the question about the change from hunter-gatherers to farmers. “It's been an enduring question in archaeology — whether we're descended from Middle Eastern farmers or indigenous hunter-gatherers,” says Thomas. Did the hunter-gatherers evolve or were they replaced? Did native populations of hunter-gatherers in Europe take up farming and herding? Or was there an influx of agricultural colonists who out-competed the locals, thanks to a combination of genes and technology?

It was found doing genetic studies that domesticated cattle at Neolithic sites in Europe were most closely related to cows from the Middle East, rather than indigenous wild aurochs. This is a strong indication that incoming herders brought their cattle with them, rather than domesticating locally. A similar story is emerging from studies of ancient human DNA recovered at a few sites in central Europe, which suggest that Neolithic farmers were not descended from the hunter-gatherers who lived there before.

So Mesolithic hunter-gatherers did not develop into Neolithic farmers, the farmers moved in and displaced them. But truthfully, doesn't the farmer-lactase gene partnership seem a little too neat?