>Return-Path: [log in to unmask] >Date: Wed, 19 Jul 1995 18:10:18 PDT >X-PH: V4.1@mail >From: Daniel Blackburn <[log in to unmask]> >Subject: Milk, sweat, and reprints >To: "katherine a. dettwyler" <[log in to unmask]> >X-Sender: [log in to unmask] > >Hi Kathy, > >I sent along the reprints the other day, so you should get them soon. > >The old "sweat gland" hypothesis is anthropocentric. Sweat glands in >humans are eccrine glands, which only in primates produce a watery >solution for evaporative cooling. In most mammals, eccrine glands are >largely confined to the digital pads, where they increase friction and >tactile sensitivity. This is an unlikely position for a precursor to the >mammary gland. > >Any explanation for the evolution of mammary glands has to begin with the >situation found in mammalian ancestors, not highly specialized forms such >as primates. The Mesozoic ancestors of mammals were small, rat or mouse >sized creatures which almost certainly (like living mammals of that size) >had no true sweat glands. However, these ancestral forms would almost >certainly have had the standard mammalian complement of glands of the >eccrine, apocrine (scent-producing), and sebaceous (oil-producing) >varieties, as are retained by all living mammals (at least >developmentally). > >I suggested in my 1991 paper in Mammal Review that based on features of >development, anatomy, physiology, and biochemistry, mammary glands were >more likely to have arisen from sebaceous or apocrine glands than from >eccrine glands, and may have originated by combining features of the first >two gland populations. If this explanation is correct, then mammary >glands are a neomorphic feature, an innovation that was not simply a >modified gland, but an organ that co-opted several pre-existing features, >(including developmental patterns, epithelial-mesenchymal interactions, >and metabolic pathways) into a new combination never before seen among >mammals or their ancestors. Thus, the mammary gland is "special", not >simply a modified gland, and not derived from anything as >prosaic as sweat glands.... a fitting origin for the feature to which we >mammals (probably) owe our current success. > >How about if I send you a copy of the Abstract to my 1991 paper for >potential posting; and if you want any of the above information as well, >you can include it. > >The 1991 paper still seems to be the latest (but probably not the last!) >word on the subject, and is also a good guide to the other hypotheses that >have been put forward. With the abstract, I can enclose my email and >homepage addresses; that way, if anyone wants to see the article, they can >seek it out themselves or mail me a reprint request. > >Dan > > 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