It is the intensity of ultraviolet radiation that varies from Equator to
poles, not the total hours of sunlight over the course of a year.  The
Equators get direct, intense UV radiation year-round.  The farther you go
from the Equator, either north or south, the less the intensity of the UV
radiation, as the rays strike the earth at an angle.  At the poles, you have
very low levels of UV radiation.  This is why you see a clinal distribution
of skin color away from the Equator in either direction, when you look at
the populations who were living there prior to massive migrations and modern
transportation.  Because dark skin is adaptive in protecting the body from
the harmful UV radiation, which breaks down circulating folic acid and leads
to pregnancy losses, as well as protecting other micronutrients in the blood
stream and protecting against cancer.  People who live near the Equator have
very dark skin, because this skin color is adaptive there.  As you move
farther north or south the skin color gets lighter and lighter (lighter in
north Africa than Zaire, lighter in northern Italy than southern Italy,
etc.), as there is less need for protection from the UV and more need of
Vitamin D to ensure proper calcium absorption.  Anyway, this isn't related
to breastfeeding, so I'll stop, but it isn't the total number of hours of
sunlight over the course of a year, but the intensity of the UV radiation
that makes the difference.

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Katherine A. Dettwyler                                email: [log in to unmask]
Anthropology Department                               phone: (409) 845-5256
Texas A&M University                                    fax: (409) 845-4070
College Station, TX  77843-4352