Re: milk and human sociobiology
Larry Caldwell (email@example.com)
24 Jan 1997 00:14:06 -0800
In article <firstname.lastname@example.org>,
email@example.com (omar shafey) wrote:
> The hypothesis suggests that in areas where people were able to synthesize
> Vitamin D from sunlight (absorption by melanin) the necessity of digesting
> milk for Vitamin D was obviated. A selective advantage accrued in
Vitamin D is synthesized by the action of ultraviolet on cholesterol in
the skin. Melanin actually reduces the efficiency of the reaction.
Milk is not a natural source of vitamin D, though it can be enriched by
exposing the milk to an ultraviolet source.
> populations in which adults became lactose intolerant because limited milk
> supplies would then be consumed primarily by children (who need it most)
> instead of by the adults. Thus, the gene for lactose intolerance would
> become more prevalent. (This may suggests that the gene could be selected
It's likely that the whole adult human race started out lactose intolerant,
and dairy food sources have selected for retention of infant enzymes.
In all human populations, at least some individuals retain lactose digesting
enzymes into adulthood. Lactose tolerant individuals can easily be found
in native American, Polynesian, and Australian Aborigine peoples whose
ancestors have no history of domestic milk animals. The majority of
Northern Europeans are lactose tolerant, but that is the exception rather
than the rule.
> In Europe, the populations' lack of melanin (and long winters with
> relatively little sunshine) meant that digestion of milk was necessary to
> obtain Vitamin D and so any lactose intolerance genes would prove to be
> detrimental and the gene would not become prevalent.
As above, lack of melanin actually increases vitamin D production. If
a selection force has operated it probably stems from having lots of
fresh milk and very little else to eat through a long winter. In areas
warm enough that milk automatically ferments, lactose would not be
a significant factor in the diet.