>Marsha wrote, presumably half-facetiously,
><< I often wonder how long the earth would have continued to be populated if
>5% of its infants each year were unable to receive enough milk starting when
>humans
> first appeared! >>
>
>Considering how much of human history the infant mortality rate was above 5%,
>I'd have to say that the earth's human population would get along just fine,
>in terms of self replacement; it would just be sadder than it is now.


There is a big difference between an infant mortality rate being above 5%
and having 5% of all mothers not able to lactate and therefore not able to
have children.  In Mali, where the infant mortality rate can be as high as
25% of all children dying by age 5, women still have many surviving
children.  A mom may have had 14, with 9 living til adulthood, or had 9
with 6 living to adulthood.  You still get plenty of children to carry on
the species.

But if 5% of the mothers in the population could not lactate, then chances
are good that most/all of their babies would die (unless other women took
over the nursing duties for them).  Still, women who couldn't lactate
probably would have fewer surviving babies to pass on the genetic
predisposition to not being able to lactate, therefore, it would disappear
in the population.


----------------------------------------------------------------------------
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Katherine A. Dettwyler, Ph.D.                         email:
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Anthropology Department                               phone: (409) 845-5256
Texas A&M University                                    fax: (409) 845-4070
College Station, TX  77843-4352
http://www.prairienet.org/laleche/dettwyler.html

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