The Duchess of Zeon wrote:
STOP.
Read that again and then read it again. Then think about where humans live now.
That's right.
Everywhere.
Mmmm.. yes and no. That's a broad answer if you're judging time by evolutionary standards. Yes, humans are VERY quick adapters.. on the thousand year scale. Which is not to say they're NOT quick, actually they're very damn quick.. but not in the next generation or even current generation sense without the help of technology. But you're talking about hunters and gatherers, essentially next week adaptation.
Without help from the resources on hand (i.e. sources of calcium and the selective ability of certain groups of people to process lactose), it requires time for a selective trait within a geographical confine to become widespread. Granted, if it's a heterozygous advantage.. it'll occur really quickly.. probably within a few generations.. but as I said.. up to that few generations those without the advantage are going to have problems.
Let's take the most basic example, sickle cell anemia. Sickle cell under homozygous situations is extremely deadly without modern medical care, but heterozygous is wonderfully advantageous to surviving in malaria ridden areas. Now, it fluctuates quickly depending on migration and can drop to normal selected out in the absense of malaria of advantageous qualities extremely quickly and likewise rise as well. However, the factor is GENERATIONS.
And that was my point. While yes indeed, humans are quite adaptable to a given situation given the proper tools, resources and time. It also requires on some part for advantageous traits to be selected for and disadvantageous ones selected against. And as you know.. that doesn't happen over night.. and in particular environments.. it can be selected quite handidly.
So I'm not saying you're wrong.. from a certain point of view. Humans ARE incredibly versatile. But just not quite THAT versatile. In fact, there's been some hub bub about bone deformities of early graves in Northern Europe which could help explain the selective trait for lactose ingestion.. interesting stuff.
And it's spelled Sherlock.