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Unformatted text preview: h a lot of practice. Young
males often struggle to successfully penetrate a female spotted hyena.
Only through years of repetition do they get good at it. Even then the
female has to provide a lot of cooperation. Appearances to the contrary,
female hyenas’ pseudopenises differ considerably from penises both
functionally and anatomically. During copulation the female’s “penis,”
or enlarged clitoris, serves as the opening to her vagina. When the male
is properly positioned the female can invert her clitoris, pulling it up
inside of herself like turning the sleeve of a long-sleeved T-shirt outside
in. That gives the male access to her vagina and creates the possibility
of fertilization and pregnancy.
Though successful fertilization is the key to hyenas’ future, for the
female it can be an unpleasant prospect. At birth the baby hyena enters Where Our Sexes Come From 103 the world through the same pseudopenis that the hyena uses for urination and copulation. That requires a lot of changes.
“During birth it [the pseudopenis] stretches out so much that it
looks like a water balloon.”18 And sometimes that balloon bursts. In
fact, during first pregnancies the clitoris must break open for successful
delivery. After that some females never become pregnant and give birth
again. Others die. Even when everything goes right, or nearly right,
with the mother, in captivity about 60 percent of hyenas are stillborn.
That is a trade-off for the powerful, dominant females that have
made the spotted hyenas as successful as they are today. The unusual
development of female spotted hyenas provides the edge they need to
compete successfully, even against males, for too little food.
Spotted hyenas have been around for about seven million years,
all that time hunting prey, mating, reproducing, raising their young,
and surviving in a harsh environment. And all that time the females
have had an anatomical “problem” that, if they were humans, we
would insist on fixing. For spotted hyenas, intersex is simply a way
Androgen Insensitivity Syndrome
Other genetic changes that affect androgens can lead to male babies that
look like, or very nearly like, baby girls.
The process that leads to the formation of penises and scrotums during fetal development requires not only the production of androgens by
both the testes and the adrenal glands but also the normal expression of
receptors for these hormones. That is, the hormones—like testosterone
produced by the testes and the adrenal glands—normally bind to specific molecules on the surface of cells in the developing genitalia, like a
key slipping into a lock.
When the lock and the key come together just right, a baby boy
begins. When the androgens (the keys) are present but the receptors
(the locks) have changed, nothing happens. This condition is called
complete or partial androgen insensitivity, depending on the degree of
receptor change or loss. In androgen insensitivity the developing tis- 104 Between XX and XY Hormones bind to specific molecules on the surface of cells in the developing genitalia. sues—even though bathed in androgens—cannot use these hormones.
Then 46,XY babies are born that cover the range of possibilities from
nearly normal baby boys to almost perfect baby girls, even in the presence of a normal Y chromosome with SRY and normal levels of male
androgens. The gene responsible for the normal production of androgen receptors is called AR, and it is on the X chromosome.19
Because AR resides on the q arm of the X chromosome, losing pieces
of the q arm can have dramatic consequences during sexual development. Nearly one hundred different known mutations in AR cause partial or complete androgen insensitivity.20
Even though their sex chromosomes are normal, these babies have
been called pseudohermaphrodites because of the disconnect between
their sex chromosomes and how they appear to us. Nicky Phillips
Location: British Columbia, Canada
“Recently I had to fill out a form for Census Canada. I found one of the
questions to be problematic. It wasn’t one of those hard ones where you
were expected to calculate your income or the time you spent taking
care of seniors, it was the one which asked, ‘Are you male or female?’”
Nicky is a smart, fast-thinking, and thoughtful woman living in
western Canada. She is sixty-four years old and retired. She is also Where Our Sexes Come From 1 2 3 4 5 105 6/7 Schematic representation of a grading scheme for clinical classification of AIS.
Grade 1: normal masculinization in utero
Grade 2: male phenotype with mild defect in masculinization
Grade 3: male phenotype with severe defect in masculinization
Grade 4: severe genital ambiguity
Grade 5: female phenotype with posterior labial fusion and clitoromegaly
Grade 6/7: female phenotype21 pretty good with this sort of question. She has to be. Nicky is a woman
with complete androgen insensitivity syndrome.
“I checked female, which is the sex on my birth cert...
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This document was uploaded on 02/04/2014.
- Spring '14