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>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