I’m lactose intolerant. When I drink milk it feels like an angry woodchuck is paddling around my guts building a little dam made out of skulls.

The mechanics of lactose intolerance are pretty simple. Lactose is a sugar found in mother’s milk. Lactose is digested by an enzyme called lactase. After weaning, a baby wouldn’t normally have lactose in his diet and his body will stop producing lactase. This is why babies can drink mother’s milk all day but if I eat a peanut buster parfait, I’ll be reduced to tears. My lactase gene was switched off decades ago.

I’m not so strange. The ability to digest lactose in adulthood is actually very unusual. A small population of northern Europeans from the region including the Netherlands, northern Germany, Denmark and southern Norway are lactose tolerant.

But why? Why isn’t Heinrich Von Milch’s lactase gene switched off after infancy? Because north central Europe was the center of European cattle-breeding and one of the first farming cultures. So the human population from that area developed the ability to digest lactose through adulthood as an adaptation to the ready availability of cow’s milk. This is a fascinating example of how the human genome responds to cultural changes.

What this shows is that real life application of the paleo nutrition plan is tricky. Foods that are genetically optimal for my European wife are decidedly sub-optimal for me. The bottom line is, if a particular food makes you look or feel like crap, don’t eat it.