As you probably know, everyone should drink milk. Lots and lots and lots of milk. All your life. Or so says the American Dairy Industry, often using those sexy posters of famous people with milk smeared on their faces.
The truly amazing thing about those posters is that the people in them more often than not seem to have an ethnic identity that I, as a trained Biological Anthropologist (and thus keeper of this sort of knowledge) can easily see contraindicates milk consumption. Most of these individuals would likely be unable to break down the lactose in the milk because they have the “wild type” or “normal” allele that facilitates the shutdown of lactase production some time in early life.
Now let’s be clear about this. We humans are mammals, and as mammals, we drink mother’s milk while young. This is facilitated by the production of lactase, an enzyme that breaks down the main energy bearing molecule in milk, the sugar lactose. But your basic well adapted mammals should not bother producing the enzyme lactase after weaning normally occurs … maybe a few years after in a long-lived mammal like humans … because it is inefficient and potentially risky to produce enzymes you don’t need.
Why is it inefficient? Well, there are thousands and thousands of enzymes and if we just produced all of them all the time in all our cells, that would be really costly of raw materials and energy, both of which are required to produce them. So, evolution has shaped, via the brilliant designer of Natural Selection, our multicellular bodies to produce enzymes only in the cells they are needed in (from which they may be exuded on occasion, as is the case with lactase, a digestive enzyme). This is much more efficient. By extension, the system should be (and usually is) selected to produce specific enzymes when they are needed instead of all the time from birth to death. By doing this we save a lot of raw materials and energy.
