Breakfast Hypotheses: Milk & Adaptations
I’m currently at my folks place packing up some stuff for my move to Seattle. Anyways, just had a bowl of cereal with “Lactaid” milk. It’s milk that’s had the lactose removed to help those with lactose intolerance, which is probably most people - and actually most mammals.
I started to wonder why we have such little trouble with lactose as babies, yet do have trouble even as we begin to turn into young adults. Obviously, the chemical reason is a lack of lactase. But why does that happen?
Here’s my hypothesis: Perhaps, just perhaps, it’s actually an evolutionary adaptation to avoid having adults (those who can fend for themselves) merely leeching off of the females, especially since that nutrition is necessary for the young who may starve if there isn’t enough. (Alternatively/additionally, there may also be an advantage in encouraging young adults to go find other sources of food so that they do not become reliant on dear ol’ mommy all the time.)
Now, I don’t know if the discomfort of lactose intolerance is enough to deter a hungry animal, or if this is a strong enough pressure for an actual evolutionary change - but it doesn’t seem ridiculous, it’s apparently a fairly consistent phenomenon for mammals, and I’m intrigued - and I think the hypothesis is somewhat bolstered - by the finding of lactase persistance - that some human(s populations) continue to make lactase into adulthood. This has been a topic of much interest to geneticists and evolutionary biologists, who believe that it’s a recent adaptation arising from centuries of dairy farming. Thus, there are genes to allow this and they are influenced by at least some environmental pressures.
But while I’ve heard much about the evolutionary advantage of lactase persistance, I’ve never heard anything about the evolutionary rationale for lactose intolerance in the first place - which is why I find this idea fascinating, especially since it’s based on similar principles. (Again, “nothing in biology makes sense except in the light of evolution”.)
So, that’s today’s breakfast hypothesis. Thoughts?