--- In FairfieldLife@yahoogroups.com, "authfriend" <jst...@...> wrote: > > --- In FairfieldLife@yahoogroups.com, "shempmcgurk" <shempmcgurk@> > wrote: > <snip> > > I'm not a biologist or geneticist but I think that > > 10,000 years is more than enough time for a species > > to select genetic traits. So I think you strengthen > > my point by reminding us that it's "only" been > > 10,000 years that dairy has been a part of the human > > diet. > > In fact, in populations that continued to drink milk > beyond weaning age, there *has* been genetic > adaptation, at least with regard to lactose intolerance. > But dairy has not been part of the human diet universally > by any means since 10,000 years ago, so the gene that > turns off the ability to digest lactose after weaning > persists, in widely varying percentages among groups > with common ancestry (Ashkenazi Jews and others of > Northern European ancestry, for example, have a very > low percentage of lactose intolerance, whereas African > Americans have a very high percentage).
Addendum: Point being that diet has varied widely among different groups over 10,000 years depending on many different factors, so adaptation to different kinds of foods has varied widely as well. Talking strictly through my hat here--knowledgable folks please speak up!--I would guess that since lactose intolerance is a matter of a single gene, adaptation can take place fairly quickly; whereas adaptation to eating grains and beans rather than meat has to do with the physical structure of the digestive system as well as with enzyme production and other elements, so it may occur much more slowly.
