So, for the longest time, humans had a gene that turned off the gene that produced lactase (the enzyme required for digestion of lactose, found in milk) early in life. People didn’t drink milk after weaning, so the production of lactase was a no-benefit use of energy.
Then, a group of people in Europe began herding cows some 9,000 years ago, and eventually started drinking the milk. Sure enough, a mutation occurred in these people that prevented the lactase gene from being switched off. Today, the people geographically close to those herders (Dutch and Swedes) almost all have the mutation, and the further away, the fewer have it.
In Africa, research has shown three separate groups of herders have three different mutations (and each different from the one in Europe) that accomplish the same end. Both mutations disable the gene that switches off the lactase. Knowledge of how mutations occur in humans indicates that the times these mutations occurred coincides with the known beginnings of their herding activities. The mutation proved wildly successful, as the owners could not only benefit nutritionally from the milk, but in times of drought could avoid dehydration that the lactose intolerant people could not.
Four separate groups of people, with the same evolutionary influences, developed four distinct mutations that imparted the same direct benefit. Seems a pretty clear genetic adaptation that is directly attributable to environmental pressures. Natural selection at work in humans in very recent history.
This mutation has interested me. I have read of cases where individuals were able to drink milk (ie still producing lactase) and then for some reason or another stopped drinking milk for an extended period of time. Once they try drinking milk again they find that they are now lactose intolerant (ie no longer produce lactase).
Is this more about the body producing the enzymes that it needs (ie as long as one continues to consume milk their body will continue to produce lactase) or how does that fit into the mutation? I’m no geneticist and I didn’t even stay at a Holiday Inn last night so don’t freak out about evolution on me here. I’m just happy that I seem to be one of those freaky mutants who can continue to produce lactase.
“This mutation has interested me. I have read of cases where individuals were able to drink milk (ie still producing lactase) and then for some reason or another stopped drinking milk for an extended period of time. Once they try drinking milk again they find that they are now lactose intolerant (ie no longer produce lactase).”
I stopped drinking milk for about 4 years and started drinking it again about a year ago. I used to drink a lot and continue to do so, but when I first started to drink milk again after that time off I was somewhat lactose intolerant. Now I drink up to 1/2 gallons a day no problems.
I don’t think that the expression of the gene producing lactase is affected in an individual by the environment (barring mutations, of course). I’m no geneticist, either. I do know that I was lactose intolerant as an infant, and again from at least high school into my mid-20s, and something switched on/off and I became lactose tolerant (for the most part). Go figure. Probably had to do with puberty.
“This mutation has interested me. I have read of cases where individuals were able to drink milk (ie still producing lactase) and then for some reason or another stopped drinking milk for an extended period of time. Once they try drinking milk again they find that they are now lactose intolerant (ie no longer produce lactase).”
This might be the case of a food allergy. Rather than the “mutated” gene being turned on or off some people might simply be allergic to some component in milk, and when they stop drinking it regularly they become hypersensitive. Once they start exposing themselves regularly to milk again they stop reacting to it. An interesting news article that talks about studies at Duke where the researcher are “desensitizing” people with food allergies by controlled exposure to the foods that will kill them. i.e. do not try this at home.
You may already have heard of it, but there’s a book called “Before the Dawn” that is very interesting (at least the first half was…I wasn’t a fan of the author’s writing style, and haven’t finished it). The book documents much human evolution that occurred very recently.
Interesting. I’m unsure about the specifics, but there are other interesting cases. There are people on the planet that are immune to the HIV virus. They simply don’t produce the protein that the virus attaches to. It is a random and harmless mutation. Just as random variability makes some of us tall and some of us short, variation goes right down to the genetic level. Pretty fascinating stuff.
