How Biology Affects Gender
Chapter 4
Genetics
Terminology
Genotype- genetic blueprint for potential traits- DNA plan locked in each
cell that directs development of the entire body.
Phenotype- outward expression of the genetic code
Genetics do not determine your outcome in a vacuum- environment shapes
(modifies) development of genetic tendencies (PKU disorder)
Gender determination
Zygote- the single cell formed from union of sperm and egg- holding the
complete genetic code, even the process of aging
Mitosis- process of cell division for all cells except sex cells- produces 2
cells with identical chromosomal makeup of the original cell.
Meiosis- cell division resulting in daughter cells with half the number of
chromosomes as the original cell- cell division that produces the sex cells.
DNA- deoxyribonucleic acid- makes up the genes that are held on the
chromosomes (about 20K genes on each chromosome) You can see why the
Human Genome Project took some time.
Genetic sex is determined by the combination of XY (male) or XX
(female) on the last pair of chromosomes- the sex chromosomes. Fathers
determine sex of child. The Y is specific to development of male sex organs.
More males are conceived, due to the speediness of the lighter Y-carrying
chromosomes, but not as many males are born due to fragility & higher numbers
of genetic disorders. This pattern continues all through life, leaving far fewer men
per women at the oldest ages. This is not just about genetic vulnerability, but also
about male roles and jobs being more risky. Estrogen has a protective effect on
women, also, which men don’t get.
Genetic Complications
Sex-linked inheritance- traits are determined by genes located on the sex
chromosomes- usually the X. Since women have 2 Xs, they are more likely carriers of
sex-linked traits, but men are more likely to express the trait in their phenotype. 200
disorders are X-linked- color blindness, night blindness, hemophilia, Duchenne’s
muscular dystrophy. Two Xs give women lifetime protection in many ways.
Turner’s syndrome results when the sperm cell contributes neither an X
or Y, so the girl who results has female genitalia, but don’t menstruate, don’t develop
secondary sexual characteristics at puberty, are very short, average intelligence, but many
learning disabilities and poor spatial skills. Without ovaries, they lack gonadal hormones,
are infertile, and yet due to socialization and feminine gender identity they develop in
many ways like other girls. It tells us socialization is critical in developing gender-related
behavior patterns and identity.
Sex Hormones
Terminology
Hormones- chemicals released into the body by one organ or gland that
influence the activity of other organs, even the brain. There is considerable overlap
between the sexes in levels of some hormones. Three types of sex hormones:
Estrogens – “female” hormones- more abundant in females. They
regulate menstrual cycles and produce female secondary sex characteristics.
Androgens- “male” hormones- more abundant in males. They are
produced by adrenal glands in both males and females, as well as in testes of men. The
most abundant form is testosterone. Much higher in men after puberty. Fluctuates
annually, highest between July and November, as well as on a daily basis- peaking
around mid-afternoon when levels are high, during the morning when levels are low.
Progesterone - secreted by the ovary which regulates the
menstrual cycle and maintains pregnancy. Present in males as well. Also relates to
promoting milk production following pregnancy.
Gender Categories- not as cut and dried as one thinks. One can assess sex based
on genetics, genitalia, hormone levels, gender of rearing, or internal sense of being male
or female- gender identity. Usually these categories are consistent, but not always.
Prenatal Development- the default sex is female. Without a Y chromosome, we
continue development as a female. With a Y, we get genes called the testes-determining
factor (TDF) which determines if the primitive gonad of the fetus develops into testes.
Then the testes produce androgens and a hormone called mullerian-inhibiting substance
(MIS). These both cause the wolffiian duct to differentiate into the male internal
reproductive system (epididymis, vas deferencs, and seminal vesicles) and the
mullerian duct disappears. This happens between 7 & 8 weeks prenatally.
With XX fetuses, the lack of androgens causes the wolffian duct to remain
undeveloped, and the mullerian duct will differentiate around 10 – 12 weeks (Into
fallopian tubes, uterus, and vagina) External genitalia develop from the same
embryonic tissue.
Consequences of Prenatal Hormonal Conditions- we can better understand the
effects of hormones by studying people who were exposed to abnormal levels of prenatal
hormones. We will see what is biologically related to hormone levels versus what is
socialized into us at a very early age.
Congenital Adrenal Hyperplasia (CAH)- genetic females (XX)
prenatally exposed to high levels of androgens during the critical period of gonadal
differentiation. May develop masculinized genitals. It is a recessive genetic disorder in
which the body’s adrenocortical glands secrete high amounts of adrenal androgens. These
girls have an internal female reproductive system because the high androgens don’t occur
until the internal system has developed. Externally, CAH girls have masculinized
genitals- but they don’t look completely masculine- often called “ambiguous.” Most are
raised as girls unless the parents don’t realize they are genetic girls. They usually have
some reconstructive surgery in infancy to feminize their external genitalia. They also
need hormone therapy to develop in the female pattern. Their behaviors are described as
tomboyish, very active, and they often prefer boy’s toys. They seem less interested in
traditional female pursuits regarding babies, dolls and parenting. They are not more
aggressive, and don’t have better spatial perception than other girls however. Gender
identity is feminine. They display wider gender role variability- more masculine
behaviors than other girls. This may be as a result of parents treating them slightly
differently since they realize they had masculine parts originally.
Complete androgen insensitivity syndrome (AIS)- genetic males (XY)
who are insensitive to androgens and so develop female genitals. Their penises resemble
clitorises, but there are no internal female organs. They may be raised as girls until
puberty when they fail to menstruate. There is breast development though, indicating
sensitivity to estrogen. They develop a female gender identity, due to gender of rearing.
This indicates socialization is more important than sex chromosomes in developing
gender identity.
5-Alpha reductase deficiency- recessive disorder that causes (XY) males
to develop normal internal genitals. But due to a deficiency of a steroid called 5-alpha
reductase, the boy fails to develop external male genitals. They are usually raised as a
female with a feminine gender identity during childhood. At puberty, though the testes
begin to produce testosterone, causing masculine secondary sex characteristics to
develop- even a penis and scrotum. Often these girls accept a male gender identity at
puberty. This suggests biology is responsible for gender identity, not sex of rearing. This
condition is fairly common in the Dominican Republic, and since males are highly
valued, the transition to male identity is not viewed negatively. Other studies show that
the culture did discriminate against these individuals, never fully accepting them as
normal males.
Diethylstilbestrol (DES)- between the 1940s and 70s some pregnant
women were given DES to prevent miscarriage. There were no negative effects
recognized at the time, but it was found that DES, an artificial estrogen, acted like
testosterone on the brain of the developing (XX) baby. While it didn’t masculinize their
genitals, it did show up in differences in some cognitive tasks. These girls, who were
raised as girls, showed strengths on visual-spatial tasks, more lateralized performance
which is more common in men. It also linked to developing cervical cancer in adulthood.
DES girls look like girls and have been raised as girls, so the behavioral differences seem
related to hormone exposure on the brain during development.
Hormones and Development- hormones act in concert with the environment to
create gender identity. Gender inconsistencies show that there may be more than 2 simple
categories of gender.
Commentary: How Many Sexes Are There? Sterling suggests that sex lies on a
continuum with males and females lying on the outside of the continuum, and intersexed
people falling in between. Hermaphrodites have both ovaries and testes. In the past,
people with ambiguous genitalia often had surgery in infancy to normalize genitalia, but
this procedure was fraught with risks- impairment of sexual function, identity confusion.
The practice today is more often to wait and see what gender the person develops.
The next surge of hormones comes during puberty, as people reach sexual
maturity. Menarche is first menstruation, as the internal organs respond to increases in
female hormone and fluctuations of those surges. The pituitary releases folliclestimulating hormone (FSH) which triggers the follicles in the ovary to prepare and egg
for release. Ovulation occurs as the egg matures and follicle ruptures, releasing the egg.
This is facilitated by FSH and LH (Luteinizing hormone). The corpus luteum releases
the egg and secretes progesterone. This causes LH levels to drop, the corpus luteum to
disintegrate. Then estrogen and progesterone levels drop if there is no fertilization,
signaling the release of the tissue built up in the womb into the menstrual flow. If the egg
is fertilized, however, it can implant itself in the endometrium of the uterus and begin to
grow. A woman’s eggs and ovaries decline over years, resulting in declines of estrogen
and healthy eggs. Menstrual periods become erratic. Menopause occurs when there has
been an absence of menstrual periods for a year.
Hormones and Behavior- testosterone influences aggression and sexual
behavior, libido. Higher levels of testosterone correspond to higher levels of both drives.
Sexual activity- most clearly related to hormone levels, especially
testosterone. This applies to men and women, although women never have a fraction of
the level that men traditionally have. Men with lower desire can be treated with doses of
testosterone and see improvement in desire and function. Women can be treated with
lower doses of testosterone and see their libido increase. In post-menopausal women a
combination of estrogen and testosterone results in higher levels of sexual desire, more
frequent sex, and more orgasms. Normal shifts in hormone levels in women’s’ bodies
don’t seem to relate to sexual interest, although some studies indicate higher drive around
ovulation (which makes evolutionary reproductive sense). But getting a true measure of
women’s interest is difficult because it is so related to their partner’s drive and other
environmental influences. Some women are more interested in sex after menopause due
to the freedom from pregnancy and greater independence found at that age.
Aggression- men do display more overt physical aggression than females,
related to testosterone levels. In the military though, some training of females has been
linked to protection of young. Women can be aggressive in protecting their children.
Sexual orientation- has been related to exposure to hormones prenatally.
CAH girls are 4 – 5 times more likely to be homosexual or bisexual than other women.
Even so they are more likely to be heterosexual than homosexual overall.
Brain sex- hormones do sensitize parts of the brain- especially the
hypothalamus. This may produce a set of behaviors or interests in sync with the hormonal
exposure.
Higher general activity level is associated with higher prenatal
testosterone exposure.
The Brain is being more accurately mapped and understood with the help of magnetic
resonance imaging (MRIs) and positron emission tomography (PET scans.) Are there
anatomical or functional differences between the sexes that make us who we are?
Hormonal Influences – hormones circulate through the bloodstream, even into
the brain. Brains are gendered due to the differing amounts of female vs. male hormones.
Hormones do create some measurable sex differences. They occur in two ways:
Activational- when hormones temporarily activate a particular behavior,
but don’t create any structure. Testosterone elevates sexual interest & activity. These
effects occur after the brain is fully formed.
Organizational- prenatal hormones sensitize cells in some part of the
brain so the structure responds to the hormone. This results in a permanent change in an
anatomical structure. Hypothalamus in the limbic system regulates feeding, drinking,
appetites of all sorts, body temperature, activity level, sexual drive, and hormonal
secretions. It is sensitized by a bath of prenatal hormones, triggering different hormonal
patterns at puberty. IN females the hypothalamus secretes gonadotropic-releasing
hormones which trigger the pituitary to release FSH and LH, which begin menstruation.
Evidence for other structural differences due to exposure to prenatal hormones is more
elusive.
Hemispheric Lateralization- the two sides of the brain- hemispheres- are
connected by a band of neural fibers called the corpus callosum. This connects and
coordinates the activities of both sides of the brain. The brain is lateralized- specialized
to do different activities on different sides of the brain. This occurs prenatally depending
on which side the fetus primarily rested on. The other side became dominant due to
greater mobility on the other side. So brain dominance relates to handedness. Right
handed people show more activity on the left side of the brain, especially for verbal tasks.
The right side is more activated to do visual-spatial tasks. MRIs have shown that men
generally have more lateralized brains, meaning that parts of the brain that are activated
are more discrete in men, and more homogeneous in women. (More parts of the brain
light up in women doing verbal tasks than in most men.) This does not translate to greater
ability in general in men or women, but more men do have reading disabilities. This may
be due to using only one side of the brain for these tasks. It also shows up in old age if
men or women suffer a stroke. Women will more easily retrieve verbal functions than
men will after damage. This aphasia is 3 times more likely in men than women.
Sex and Brain Size – men’s brains are generally larger than women’s, even
controlling for body size. Men’s brains are slightly heavier than women’s as well, but it is
difficult to measure brain size accurately. Difference in size doesn’t imply differences in
function, speed, or accuracy, however. One area of the brain studied is the corpus
callosum. The splenium in the back of the brain is larger and more rounded in women
than men. The function of the splenium is to tie together parts of the left and right
hemispheres in control of speech and spatial perception. Women’s larger splenium may
account for women’s advantage on some aspects of speech production and
comprehension. Does it also have some effect on men’s advantage on spatial perception?
It is also true that more differences in splenium size are found within same-sex groups
than between the sexes. Many studies find no difference in splenium size. And how to we
interpret this difference when we find it? Interpretation is not clear on this issue. But
people are interested in these findings since they naturally see gender differences and
want to understand the source of them. It is not so simple, however.
Biological Theories of Gender- these represent the “nature” side of the nature-nurture
controversy:
Biosocial Theory (Money and Ehrhardt)- this theory states that a series of critical
events lead to gender-typed behavior.
Conception- we get either XX or XY chromosomes. This leads to
development of fetal gonads- testes or ovaries, with the corresponding hormonal
secretion. Hormones start the development of the genitalia & create sex differences in
the brain.
Environmental influences occur as people react to the baby’s gender.
This begins a separate socialization pattern based on sex of baby. This treatment produces
the child’s gender identity. This identity is reinforced by pubertal hormones that
produce secondary sex characteristics and sexual drive.
Evaluation- CAH girls show that regardless of chromosomal makeup,
these girls’ behaviors show definite masculinization, regardless of socialization. This
must be due to prenatal hormone exposure. The question is whether their early
ambiguous genitalia caused others to treat them differently early on. Biosocial theory
says biology merely sets the stage for social reactions. It is biology and social experience
together that produce gender. In androgenized females who were originally raised as
males until later when they were discovered to be female. Those who were relabeled as
female before 18 months successfully adapted a feminine gender identity. Those who
were relabeled female after age 3 years had problems adjusting, thinking of themselves as
boys. This indicates there may be a critical period (18 months to 3 years) for
development of gender identity. After that, socialization cannot be erased in spite of
biological factors.
Featured Study: Mistakes of Gender and Gender Identity- the “experiment”
in which twins were brought to Dr. Money after one had his penis cut off during
circumcision was initially used to show the flexibility of gender after reassignment. The
little boy who lost his penis was altered surgically to have a vagina, be exposed to female
hormones, and the mother told to raise him like a girl. While Money followed the 2 for
years, assessing the reassignment as a success, later information showed this child had
gender confusion for years, to the point of suicide. When informed in his teens what
happened to him, he had corrective reconstruction and became a boy again. He had never
acted like a girl, in spite of Money’s findings to the contrary. He was so traumatized by
this experiment, that he ultimately did commit suicide. Recently I heard the brother had,
too, at this point. Tragic. Another experiment like this resulted in the child being given a
choice of genders at puberty. She chose to remain a girl, but said surgery did not make
her female- she regards herself as intersexed. 39% of those reassigned early in infancy
developed some psychopathology: gender identity disorder, deviant gender role,
depression, sexual problems. Prenatal hormones may outweigh surgical correction in
determining gender identity.
Social reactions to gender labels- parents and others do react differently to a
child according to the gender the child shows. It is disturbing to people if gender is not
signaled in some way with clothing, bows, etc. We use gender to structure babies’
worlds. So in accordance with biosocial theory, society does foster gender-typed behavior
by labeling and differentially socializing boys and girls.
Evolutionary Psychology- theory is based on Darwin’s concept of natural
selection- survival of the fittest with the object reproduction. (David Buss) We compete
for survival and the winner (most adaptive, successful) gets to pass on his/her genetic
endowment to another generation. It’s the most concrete immortality we can hope for. So
the most adaptive traits are most likely to be passed on.
Adaptive needs- sex differences occur in response to different adaptive
needs the sexes hold. Male oriented behaviors include aggression, competition,
promiscuity, concern for youth and attractiveness of partners. Female oriented
behaviors include less aggression, less concern with position in dominance hierarchy,
less promiscuous, more concerned with finding older males with resources or social
status. These basic differences have to do with relative investment in offspring. Women
invest much more deeply in offspring- with 9 months of gestation, nursing the baby, and
keeping the child alive through childhood. Men invest indirectly through provision of
resources. So women value men who are wealthy, capable of providing material
resources. Men value women who are young and fertile enough to produce children.
Evolutionary theory focuses on sexual strategies men and women use:
Men use short-term strategies. Men, with their millions of sperm
produced on demand, try to fertilize as many women as possible and
minimize their commitment to any one woman. This optimizes their
chances of producing offspring who carry their genes. They also have no
physical investment in the 9 months of gestation.
Females use long-term strategies. Women need 9 months to
produce a baby and only produce one egg per month. They need to ensure
that their few offspring will survive. So they concentrate on the long term
by mating with men who have resources and willingness to commit them
to a woman and her child. (This is true even if the woman chooses to mate
with a younger, more physically viable man on the side.)
This theory explains why women end up with most of the childcare
responsibilities. They have already made a large investment in the child
over the past 9+ months, and men have little investment at that point. Also
women are always sure that they are the mother of the child. Men do not
have that certainty. This theory is supported by the different expectations
of men and women for their partners. Men don’t need to know much of a
woman’s character to be willing to have sex with her. Physical
attractiveness is the defining trait for a short-term mate. Attractiveness is a
measure of health. Women do show a preference for men who have
reliable and successful careers. They use short-term dating strategies to
size up the potential of a man for a long-term relationship. They do look at
aspects of character in this search. Stinginess or promiscuity don’t bode
well for the long haul.
Evaluation- Bem believes this theory underestimates the power of
culture on this process. This is especially true since humans have shown
great power in transforming their environments as necessary. This theory
shows that gender differences have evolved over time, and maybe aren’t
very open to social change. (My personal view is that they do evolve, but
it is a slow process because so much in the environment is geared toward
keeping society stable and recreating the past traditions.) Buss has been
criticized for using people’s stated preferences as evidence for his theory.
What people say they want and what they actually choose are often
different. Other criticisms regard the universality of the application. Some
cultures show some differences in what is desirable in a mate.