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from "Born that way" theory
The Human Embryo's Sex Differentiation:
Why Do Men Have Nipples?
A Book Review by Louis A. Berman
Professor of Psychology (retired),
University of Illinois at Chicago
March 31, 2006 - My eyes popped when I saw the title of the New Yorker writer Mark Leyner and Dr.
Billy Goldberg's little book, Why Do Men Have Nipples? I felt, I confess, more
than a touch of envy when their book hit The New York Times Bestseller list, and
came out in a paperback edition. My book, The Puzzle (Godot Press, 2003), covers
the topic more thoroughly, and discusses the role of nipples in the sex life of
both straight and gay males.
The Puzzle argues that male homosexuality results from an interaction between
inborn and social factors, and that an important inborn factor is low brain
masculinization. Why do male brains have to become masculinized at a given stage
of embryonic development? Because for the first six weeks of life, all embryos
are proto-female. Afterwards, some male brains become more thoroughly
masculinized than others. Males whose brains are masculinized to a lesser or
minimal extent, are more likely to display gender-discordance, or to drift
toward homosexuality as a way of correcting or accommodating to their felt
deficit.
A well-trained embryologist cannot tell the difference between a male and a
female embryo if the embryo is less than seven weeks old. At that early stage of
prenatal life, there is a fork in the road of development. If there are no
hormonal changes in the prenatal environment, the embryo developes into a
female. If, however, the embryo is destined to become a male, its Y-chromosomes
trigger the production of testosterone (the male hormone), which masculinizes
the brain and genitalia (internal as well as external) of the embryo. But it
takes no female hormone to produce a female infant. (Only at age ten or later
does the female body begin to produce the hormones that transform the girl into
a woman.)
Every person begins life with a proto-female brain. Testosterone masculinizes
the brain (and genitals) of those embryos that are genetically marked to develop
as males. Almost all male genitals are thoroughly masculinized. (There are,
unhappily, rare exceptions.) But, there is some direct evidence, and lots of
indirect evidence, that there is a wide range of variation in the degree to
which the male brain is masculinized. The Puzzle argues that the
low-masculinized brain shades the inner life of the individual with female
thoughts, feelings, and wishes. This tendency, it is hypothesized, underlies
gender-discordant behavior, fear of homosexuality, and homosexual behavior. As
one unhappy homosexual man lamented, "I am a male with a female brain."
So the problem (for those for whom it is felt as a problem) or the fact of their
homosexual situation begins with the fact that we all begin life as a
proto-female, and that a few males end up with a low-masculinized brain. What is
the evidence that life begins for all of us as proto-females? We all have
nipples, that's the evidence. As Leyner and Goldberg put it, "During
development, the embryo follows a female template until about six weeks, when
the male sex chromosome kicks in for a male embryo." But before the end of the
sixth week, a pair of sweat glands on the chest has already begun to
differentiate as nipples. All infants are therefore born with nipples and some
breast tissue. As they approach puberty, the female hormones that course through
the bloodstream of girls reshape their body in womanly ways, including the
development of their breasts. Males are left with vestigial nipples, a reminder
that life begins for all of us as proto-females, and some of us are fated to
become more masculinized than others.
Professor Berman is the author of The Puzzle: Exploring the Evolutionary
Puzzle of Male Homosexuality (Godot Press, 2003). His book has won the applause
of prominent psychologists, and of the foremost evolutionary biologist of our
time, Harvard University Professor and author Ernst Mayr.
Updated: 2 September 2008
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