I have also come across the idea that breasts are modified sweat glands, but
there are other theories as well.  I have asked Dan Blackburn, a professor
at Trinity College in Hartford, Connecticut, who does research on the
evolution of lactation in mammals, to send me a 1-2 paragraph explanation of
the different theories.  When I get it, I will forward it to LactNet.  I
found him on the net while searching for "lactation" and sent him an e-mail
-- only to discover he thought his homepage was limited to his own
university and had no idea it was hanging out there for anyone to find.
Isn't the net fun?
Katherine A. Dettwyler, Department of Anthropology, Texas A&M University
e-mail [log in to unmask], specialist in infant feeding and health
co-editor of Breastfeeding: Biocultural Perspectives