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Does the Fetus Begin as Female?

The following discussion of whether all fetuses begin as female occurred
on WMST-L in April 2000.  For additional WMST-L files now available on the
Web, see the WMST-L File List.
Date: Wed, 5 Apr 2000 18:49:20 -0500
From: Diana York Blaine <dblaine @ UNT.EDU>
Subject: all fetuses female first?
It is my understanding that fetuses begin as female and then hormonal
changes instigate physiological alterations that lead to male anatomy in
some.  Is this true?  If not, what is true?  Does anyone have references?


Diana Blaine
University of North Texas
dblaine  @  unt.edu
Date: Wed, 5 Apr 2000 17:35:31 -0700
From: "A.R. Calvert" <scout @ HOYDEN.ORG>
Subject: Re: all fetuses female first?
Fausto-Sterling, Anne.  Myths of gender : biological theories about women and
men.  New York : Basic Books, c1985.

There's two theories, so far as I know.  The first and one embraced by
mainstream scientists and many feminists is the one you are asking about,
that all foeti are female until androgens masculinize the XY ones.

Fausto-Sterling casts doubt on the science around that, pointing out that
foeti are awash in a bath of hormones from the mother; it is possible that
for a female foetus to feminize "properly" that the mother's hormones must be
present.  Of course, the only way to test either hypothesis is to bring a
foetus to term outside of the presence of hormones.  Fausto-Sterling uses
this idea to cast doubt on the reliability of the former theory.

A.R. Calvert
scout  @  hoyden.org
Date: Wed, 5 Apr 2000 21:51:11 EDT
From: Susan733 @ AOL.COM
Subject: Re: all fetuses female first?
<< It is my understanding that fetuses begin as female and then hormonal
changes instigate physiological alterations that lead to male anatomy in
some.  Is this true?  If not, what is true?  Does anyone have references?>>

Zygote, embryo, and fetal sex is determined from conception, when the spern
enters the egg.  Sperm contain either an XY set of sexual chromosomes, or an
XX set.  The XY's swim faster and are less influenced by mucosal ph and
uterine changes, while the XX's live longer, thus the timing advantages for
selecting sex of the fetus.  Any zygote/fetus will be influenced by the
amount of maternal estrogen, progesterone, or testosterone circulating within
the maternal environment, but sexual genitalia per se is not changed from XX
to XY or vice versa.  It is indeed the male sperm that determines the sex of
the fetus.  It's pretty basic genetics, I'd suggest a search using the terms
gamete influence, sex embryology, sexual genetics.

Susan vanHoek
Susan733  @  aol.com
Date: Wed, 5 Apr 2000 22:23:51 EDT
From: Marty Smith <Bengeserit @ AOL.COM>
Subject: Re: all fetuses female first?
This is a story that has been told for at least 40 years.  I was told it back
when they also assumed fetuses all looked like fishes and therefore we were
descended from fishes.  If there are X and Y chromosomes, how on earth can
this it be true that Male fetuses are Females fetuses that have "evolved
further," as my male doctor told me.  He also told me that the man had to be
head of the house. --Marty

Marty Byers Smith, Retired Social Psychologist
Independent Internet Researcher
Date: Wed, 5 Apr 2000 23:35:43 EDT
From: GNesmith @ AOL.COM
Subject: Re: all fetuses female first?
The way I understand it is that, while the sex  of the fetus is determined by
the xx/xy chromosome combination, the sex organs start out looking female and
then later the penis/testicles develope in the xy (male) fetus. This is
different from having the fetus begin as female and then become male.
Date: Thu, 6 Apr 2000 07:54:50 +0200
From: Marilyn Safir <msafir @ PSY.HAIFA.AC.IL>
Subject: Re: all fetuses female first?
For the first 7 weeks the fetus is undifferentiated - and only an
examination of the chromosones cn indicate the sex. the imput of
androgenes triggers the basic orans to differentiate inot mlae organs.
Fetus with only one x chromosome ( and  no hormonal triggering develop
external femine sex organs Leading John Money to say that to get a male
hoemones must be added and the bascidc development of the fetus is femine.
There is a genetic syndrome in mlaes - inwhich the fetue is insentive to
androgens and dvelopes with an external appearance of a female.  these
twocase are what as know as intersexed.  there are many ohter sydromes.-
but in these castwo cases there is little to no differentioan of the
internal sex organs.  You might take a look aat Unger and Crawford'
Women & Gender: a faminist psychology or Janet S.Hyde  Half the human
experienc a psychology of women for chapters that go into more detail.

* Marilyn P. Safir, PhD         Internet:  msafir  @  psy.haifa.ac.il         *
* Director, Project KIDMA       Telephone: 972-4-824-0929/-0318w,/-5223h  *
* Department of Psychology      Fax:       972-4-824-0966/9014W, /0223h   *
* UNIVERSITY OF HAIFA           Telex:     46660 UNIHA                    *
* Haifa  31905, Israel          http://psy.haifa.ac.il/~kidma/
Date: Thu, 6 Apr 2000 11:26:40 +0100
From: Maria Jayme Zaro <MJAYME @ psi.ub.es>
Subject: Re: all fetuses female first?

See too Mary Sherfey's book (1966) about Jost's animal researchs, and
Ohno. It seems to have a biological programation in all sexual
animals to make fetuses females, thus male evolution is fast than
female, and need the intervention of "Y", MIS substance, etc. at
critical periodes, to finish their differentiation correctly.


Dra. Maria Jayme Zaro
Prof. Titular de Psicologia Diferencial del Sexe i el Genere
Facultat de Psicologia
Universitat de Barcelona

e-mail: mjayme  @  psi.ub.es
Date: Thu, 6 Apr 2000 12:42:20 -0600
From: Linda Holder <holder @ OCII.COM>
Subject: Re: all fetuses female first?
When an XY foetus' gonads release testosterone in the first trimester the
mother releases aromatase which converts the testosterone to estrogen. The
estrogen causes the XY foetus to differentiate (gonads descending and
formation of more pronounced external genitalia).  All estrogen production
by XX and XY foeti is suppressed by the mother during gestation.

An XY foetus that is not exposed to a significant amount of estrogen will
not differentiate and will develop feminine genitalia, however this "female"
will not develop into a woman because the XX combination is required for the
production of aromatase that will convert a females testosterone into
additional estrogen.  The reverse is also possible, an XX foetus that is
exposed to too much estrogen will masculinize, but "his" pubertal
development will be severely curtailed.

holder  @  ocii.com
Date: Thu, 6 Apr 2000 13:48:23 EDT
From: Susan733 @ AOL.COM
Subject: Re: all fetuses female first?
<<  The way I understand it is that, while the sex  of the fetus is
determined by
the xx/xy chromosome combination, the sex organs start out looking female and
then later the penis/testicles develope in the xy (male) fetus. This is
different from having the fetus begin as female and then become male.>>

All fetuses start out with either an XY or XX set of chromosomes.  When the Y
chromosome is stimulated, testicles will begin to develop, elongation of
penile tissue commences, and the interior aspects are stimulated to grow.  If
there is a problem and the Y chromosome does not become stimulated to grow
from the original primitive genitourinary tissues, there will be some degree
of aberration in the end result of genitalia.

If there is no adequate degree of stimulation of the Y chromosome, and
testicular tissue does not begin to grow, and there is a concommitant lack of
testosterone produced because the testis are underdeveloped, and if there is
an X chromosome present, then ovarian tissue begins to grow, there is no
formation/elongation of penile tissue, and the fetus takes on the growth
template of a female.  However, female development will occur if there is
only an X chromosome anyway.  Males develop first, then females -- if there
is a detected lack of stimulation to grow testes and no end target organs.
Easy to see how ambiguous sexual characteristics can develop; we all have our
unique cut-off level of inherited detection/RNA.

So we don't start out looking female -- we start out looking nebulous.

Susan vanHoek
Date: Thu, 6 Apr 2000 11:20:47 -0600
From: Judith Carla Grossman <jcgrossm @ UCALGARY.CA>
Subject: Re: all fetuses female first? (fwd)
Doesn't the answer to this question depend on the meaning ascribed to the
word female?  For instance more recent posts have differentiated between
femaleness as a function of chromosomal make-up and femaleness as a
function of external genitalia.....

Judith Grossman
jcgrossm  @  ucalgary.ca
Date: Thu, 6 Apr 2000 15:52:24 -0500
From: Suzanne Franks <sefranks @ ksu.edu>
Subject: all fetuses female first?
I started to write a private respone to Diane Blaine's inquiry:

>"It is my understanding that fetuses begin as female and then hormonal
>changes instigate physiological alterations that lead to male anatomy in
>some.  Is this true?  If not, what is true?  Does anyone have references?"

but then thought that other list members may be interested in this.

The short answer is yes, according to standard scientific thinking; the
long answer is that it's a bit more complicated than that.
Human fetuses are born with essentially two sets of proto-structures
that can develop into male or female.  The hormones and factors that
cause development of the male structures, and that inhibit development
and cause the female structures to be disassembled, so to speak,
have been identified.  Unless there are some late developments in
biology that I am unaware of, we do not know what the analagous
factors are that cause development of female structures and regression
of the male structures.  In part this is because for many years
scientists did not only not consider this a question worth investigating,
they didn't even consider it a question.  "The female is a female by
virtue of a certain lack" (I think that was Aristotle, right?) was/is the
guiding philosophy.  It took SOMETHING to make a male, but females 
happened by default.

For example, my physiology textbook (Textbook of Medical Physiology,
by Guyton, 1986, ISBN 0-7216-1260-1, p. 956) says "...the Sertoli cells
secrete several hormones that have very important functions, as follows:  
(1) mullerian inhibitory factor (MIF), secreted by the male testes during 
fetal development to inhibit the formation of fallopian tubes from the 
mullerian ducts in the male fetus..."
and on p. 988 "Human chorionic gonadotropin also exerts an interstitial
cell-stimulating effect on the testes, thus resulting in the production of
testosterone in male fetuses.  This small secretion of testosterone during
gestation is the factor that causes the fetus to grow male sex organs."  
This book, which was used for the physiology class that first year medical 
students took at Duke when I was a graduate student there in the late 80's, 
is silent on the subject of what, if anything, affects development of 
female sex organs.

Here's an interesting web site:
this is part of course notes or syllabus for a Human Biology course taught
by Robert Huskey and Fred Diehl in 1998 at UVA.  On the page noted above,
you can read about the Mullerian and Wolffian ducts and how they do or don't
develop, e.g.:
>"At the 13th week, gonads differentiate in response to germ cell invasion.
>   i.  If XX, no hormones released; Mullerian ducts develop into oviducts
>       (Fallopian tubes), uterus, and upper portion of vagina; Wolffian
ducts disappear
>       without stimulation from testosterone.
>    ii. If XY, gonads produce Mullerian duct inhibitor (MDI) which causes
>       duct to disappear; gonads produce testosterone which causes
Wolffian ducts to
>       develop into sperm collecting apparatus - epididymis, sperm duct
(vas deferens),
>       and seminal vesicle; conversion of testosterone to
dyhydrotestosterone (DHT)
>        causes development of prostate gland.
>NOTE: basic internal sex is female; male development depends on hormone
>production (testosterone, DHT, and MDI"

I consider this last statement to be a profoundly inaccurate leap of logic.
The "basic internal sex" has potential to be male or female.
Saying that the basic internal sex is female is based on acceptance of the
notion that it takes something to make a fetus male, but nothing at all to
make one female, that Female happens by default. It would be far more
accurate to say that all fetuses begin with the possibility of developing 
as either male or female, and that which way it goes depends on what factors 
and hormones the fetus is exposed to; we know which factors are important 
in male development, but not those that are important for female development.
I know that feminists have written on this, especially in the context of
discussions of individuals born with ambiguous genitalia, but cannot find
the right references just now.   A book that should be helpful is "The
Second X: The Biology of Women" by Colleen Belk and Virginia M. Borden.

Suzanne E. Franks, PhD
Director, Women in Engineering and Science Program
Kansas State University
sefranks  @  ksu.edu
phone 785-532-3395
Date: Fri, 7 Apr 2000 09:54:27 -0500
From: "Barbara G. Taylor" <btaylor @ COMP.UARK.EDU>
Subject: Re: all fetuses female first?
ALL fetuses do not start out XX or XY -- some are XXY, XYY, and a variety of
other possible combinations; it's our culture that likes the neat XX/XY
bifurcation, not nature.
Date: Fri, 7 Apr 2000 10:06:22 -0500
From: Suzanne Franks <sefranks @ ksu.edu>
Subject: female/male fetuses - correction and more discussion
In my haste yesterday I made a rather crucial and embarrassing
error in my response to the inquiry about whether or not all
fetuses begin female.  I wrote:

>"Human fetuses are born with essentially two sets of proto-structures
>that can develop into male or female."

The error, of course, is that phrase "human fetuses are _born_".
What I meant to say is that human fetuses begin development
with two sets of proto-structures....
Obviously, if it's a fetus, it hasn't been born yet.  I don't even want to
try to figure out how and why I wrote what I did in the initial post!
My apologies for any confusion I may have caused.

One person who also replied stated that the theory that the fetus
starts out female is embraced by "many feminists".  If this is true,
it's disturbing.  Mainstream science does hold this view, because, as
I noted earlier, it has not been considered an interesting question or
even a question at all to find out what factors cause the mullerian
ducts to develop into fallopian tubes with concurrent disappearance
of the wolffian ducts.  But feminists are precisely the group that should
find this to be a question worth posing!

It's even more fascinating to me that mainstream science has not taken
on this challenge, since (1) glory and fame might acrue to those who
elucidate the mechanisms and factors responsible for female sex organ
development and (2) recent scientific advances have shown that a process
called programmed cell death is important for fetal development; this is the
controlled process by which sets of cells or pieces of tissue are deleted from
a developing fetus (e.g. we initially make immune cells that would attack
our own tissue, these are selected against and "convinced" to commit
suicide, as it were).  It is a process that requires a signalling event to get
it started and it is highly unlikely that something as complex as
disappearance of the wolffian ducts could take place without the controlled
process of programmed cell death, and without an initiating signalling event.
(It's also a process that is centrally important in response of cancer
cells to certain chemotherapy drugs - they may work at least in part by
convincing cancer cells to kill themselves!)

Another poster said "Zygote, embryo, and fetal sex is determined from
conception, when the sperm enters the egg."  This is only partially correct.  
Chromosomal sex only is determined by whether the sperm contains an X or Y 
chromosome.  As other posters noted, it is possible to have XY individuals 
whose external genitalia develop to look female, XX individuals whose 
external genitalia develop to look male.  There are individuals born with 
neither XX nor XY sex chromosomes, but instead with three sex chromosomes 
of various combinations.  Various outcomes are associated with various 

The only part of this that is "basic genetics" is in the case of two sex
chromosomes, where chromosomal sex is determined by the chromosome
carried by the sperm.  Everything after that is complicated and
complex developmental biology, which is NOT genetics.  "Context is
all" said the Handmaid in Margaret Atwood's "Handmaid's Tale" and
it is certainly true here.  The context of what happens in the unfolding
of development - not just what chromosomes one has, but which genes
get expressed and when, what hormones and factors are produced
and in what quantities.  Environment and genetic inheritance are so
intertwined in developmental biology it's difficult to tease them apart at
times, especially in the complex developmental biology of humans.
Another word of caution:  when you are reading something about
what someone authoritatively tells you happens for sure or all the time,
be sure to question, in what species was this shown to be true, how
relevant is it to humans, what are the exceptions to the rule, how do
they come about, what is missing from this theory or result, and why.

One of the very depressing consequences, to me, of women being
so cut out of careers in science and engineering, is the difficulty we
will subsequently have when trying to explore the intersections of
science and engineering with our lives and our bodies.  And since
these intersections are so numerous and so frequent, this is a
dangerous state of affairs.
Suzanne E. Franks, PhD
Director, Women in Engineering and Science Program
115 Ward Hall
Kansas State University
Manhattan, KS  66506-2504
sefranks  @  ksu.edu
phone 785-532-3395
fax 785-532-6952

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