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Milk Gene

Daniel Weinreich dmw at MCZ.HARVARD.EDU
Tue Dec 20 07:58:56 EST 1994

On Mon, 19 Dec 1994, Steve Chambers wrote:

> In <bsheaff-141294221916 at lwbyppp4.epix.net> bsheaff at epix.net (Braxton) writes:
> >I am doing some research into the technological evolution of humans on
> >various continents and have heard of a genetic defect allowing adults of
> >european descent to drink milk without ill effects into adulthood. this may
> >be a trivial subject, but i could use some help or information regarding
> >this subject and i am curious as to how other genetic stocks handle the
> >digestion of milk as adults. if you can give ma any help, i'd appreciate
> >some email. i remember genetics just are my thing.
> exerpt
> ___________________________________________________
> There's another side to the coin, however, and its name is "lactose
> intolerance." Lactose is milk sugar, and to properly digest it requires a
> sugar-splitting enzyme called "lactase." It's theorized that, over thousands
> of years, the ability to produce lactase diminished in regions of the world
> where dairy farming never caught on and people did not drink milk after
> infancy. The aborigines in Australia, Native Americans, and inhabitants of New
> Guinea fit this description. In parts of Asia and Africa where dairy animals
> were kept but people seldom used milk as adults the same phenomenon occurred.
> Meanwhile, among Northern Europeans and some Mediterranean peoples, who raised
> dairy herds and depended on dairy products as important foods throughout the
> life cycle, the capacity to produce sufficient lactase emerged as a genetic
> adaptation to the food supply.
> ______________________________________________________________________________
> -- 
>  ________________________ 
> (I_lurk,_therefore_I_am!_\ ,,,                    Steve Chambers
>                           (o o)   steve at chambers.ak.planet.co.nz
> ----------------------oOO--(_)--OOo-----------------------------

I would only add that the "polarity" of the change may be the reverse of
that suggested in the excerpt (as implied by the original post, in which
lactose tolerance in adults was described as "a genetic defect").  It
seems plausable that the "ancestral state" in humans was lactose
intolerance, since dairy farming is a relatively recent innovation.  Can
adult chimps digest milk?  I bet they can't. 

Speaking as a descendent of dead white european males, I too first
conceptualized lactose intolerance as a genetic "loss", as do the authors
of the above excerpt, but that may not be the biological reality. 

Does anyone know whether the molecular genetics of lactose (in)tolerance
have been worked out?


Daniel M. Weinreich			email: dmw at mcz.harvard.edu
Harvard University 			usmail: 26 Oxford Street
Museum of Comparative Zoology			Cambridge, MA 02138
voice: (617) 495-1954			fax: (617) 495-5667

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