Biology 202
2003 Second Web Paper
On Serendip

If we were to examine a high school calculus classroom or the staff at an engineering program of a college or university, chances are that the male to female ratio would be significantly skewed. Why are women and men so different in their choices and behavior? The brunt of popular opinion focuses on the environmental cues that lead to our distinct behaviors. But is there also an innate biological basis to the choices and differing abilities between men and women? Cognitive functioning or brain processing differences in the two genders has been a point of interest and contention for many years. The purpose of this essay is to explore if neuroanatomical and genetic differences between males and females play a role in the development of "gender-specific" behaviors, perceived intellectual strengths and professional choices.

Equality regardless of gender or creed is an axiom that is crucial to our modern day society. And yet even in this 21st century, the number of women in certain "male dominated" professions, has remained fairly unchanged. Many social theorists believe that women are discouraged from such professions and that if they were given an unbiased, level playing field, that demand for these professions would be identical for both males and females. Mary Pipher, a psychotherapist for adolescent females writes, "With girls... their success is attributed to good luck or hard work and failure to lack of ability, with every failure, girls' confidence is eroded. All this works in subtle ways to stop girls from wanting to be astronauts and brain surgeons. Girls can't say why they ditch their dreams, they just 'mysteriously' lose interest" (10). Experiments have shown that women perform better when given tests that they believe are unbiased to either gender. However, it may be naïve to believe Piper's statement without studying the male and female innate differences.

Contrary to popular belief, gender and anatomical sex refer to two distinct and separate constructs as each develops at different times and in different parts of the body. John Money coined the phenomenon that codes for masculinity or femininity as "Gendermaps" (1). At a very early age and through an interaction of both nature and nurture, this gendermap imprint is established. What makes gender identification and sex so frequently parallel to each other is that gendermap evolvement is notably also induced by hormones that emanate from the developing fetus (1).

Behavioral Differences:

Though there are many similarities in the cognitive abilities of men and women, there are also discernible differences. For the most part, the behavioral differences between the intellectual capacities of the sexes have to do more with patterns of ability than the actual intellectual capacity (3). For one, attention and perception differ early on. Baby girls have been noted to gaze longer at objects than baby boys. Later they rely on landmarks and memory for guidance. Boys on the other hand, have a better visual-spatial ability such as aiming at stationary or moving targets and detecting minor movements in their visual fields more easily. The fact that males perform better in navigation seems to agree with the possible theory that evolutionarily, many of these abilities would have been important for survival in the time of hunter-gatherer societies, where males navigated unfamiliar terrain while hunting, and females foraged more nearby areas gathering food (3). Another difference is their verbal ability. Women have been repeatedly shown to excel in language and tasks that involve manual dexterity and perpetual speed such as visually identifying matching items. Men appear to have an advantage in tasks requiring quantitative and reasoning abilities and excel in math as well as science (14).

Neuroanatomical Differences:

There are epidemiological suggestions that there may be neuroanatomic differences contributing to the cognitive functioning of males and females, although the literature is by no means conclusive. While it would be ethically suspect to make any conclusions based on observational anatomic research - it is useful to distill the anatomic differences cited in the literature to date.
Comparison in size shows that the male brain is on average 10% larger than the brain of females, although women usually have a larger percentage of information-processing gray matter. A greater proportion of gray matter suggests a greater processing capacity. This explains why the belief that greater head size indicates greater intelligence is invalid in this instance. Women, albeit smaller have more efficient brains - thus explaining why the sexes score similarly on intelligence tests (9). Magnetic Resonance Imaging has shown that male brains contain more white matter and cerebrospinal fluid than females, which may contribute towards better spatial, geometrical capability (11).

Another caveat in the neuroanatomical discrepancy of the sexes is in the hippocampus, hypothalamus and corpus callosum. The right cerebral hemisphere is larger in males leading to possibly the aggressiveness typical of male behavior. One test that verifies the asymmetry is that male rats given testosterone (the principle male sex hormone), develop a thicker, right hemisphere (2). In females, the cerebral hemispheres are symmetrical, with both functioning equally in the processing of speech. This higher level of interchangeability of hemispheres may relate to increased language prowess in females (12). For all these dissimilarities, it is important to keep in mind that the above published differences only represent gross averages of study populations. They cannot and should not be used to directly prove causality, but rather a potential avenue for further exploration.

Genetic and Physiological Differences:

The genetic makeup of individuals tends to dictate physiological differences. An individual with an extra Y chromosome or XYY instead of XY genotype will not only have a different phenotype, but will be much more aggressive due to the increased "maleness". The XYY syndrome brings up another very intricate issue, criminology with behavioral genetics. XYY subjects may be more violent. Adoption and twin studies also show a genetic linkage to certain behavior. Identical twins are genetically identical, and because of their similarity of criminal behavior, it is suspected that behavior is genetically linked (15).

Infants have been shown to have differences in behavior at a young and tender age, preceding much environmental influence. One study reported that the least sensitive female infant may be more sensitive than even the most sensitive male. Female infants appear more sensitive to noise and are also more social. "They are more inclined to "gurgle" at people and to recognize familiar faces than baby boys" (8). The behavioral differences between infants of different sexes appear very early in life, indicating that the mechanism controlling these behavioral patterns is innate and not learned from society.

The difference in the sexes may begin even earlier than the cradle in their perinatal existence. In a study by Emese Nagy, the heart rates of 99 newborns were measured with simultaneous video recording of their behavior. Proving that alert newborns have a similar differences in heat rate as those found in adults: males had a significantly lower baseline heart rate than girls, suggesting that heart rate is gender dependent from birth onward (6).

Hormones also seem to play a major role in sexual differences. Sexual dimorphism according to some studies relies on the presence of androgens such as testosterone. If absent, this leads to female gendermaps. Others suggest the presence of estrogen influencing female gender. In rats, there is a region called SDN (sexually dimorphic nucleus) in the brain that is larger in males. Giving testosterone can actually increase the size of the SDN (2).

An intriguing issue is how estrogen and progesterone hormone levels are
much higher in women, and fluctuate across the lifespan, including puberty, seasonally, during the menstrual cycle and after menopause. Researchers have examined the contributions that these hormones make to behavior and learning through various tests. Females that have been exposed to high levels of testosterone such as in congenital, adrenal hyperplasia, demonstrate a more aggressive behavior as well as improved spatial skills - behavioral strengths of the opposing sex (14). Hormone replacement therapy is actually used in the medical field today for post-menopausal women. Increasing certain hormone levels will improve their attention levels, similar to the situation for adolescent girls with dyslexia, who via increases in their estrogen level during puberty show an improvement in their reading abilities.

Environment:

Although there is much evidence suggesting that gender differences be based on the natural and physiological distinctions in our bodies, the environmental and social influences certainly play a major role as well. From day one, starting with their initial noisy entrance into this world, babies are viewed according to their gender; even color coding them right away. Oh, it's a girl! God forbid if this child ends up wearing blue - she may have a social identity crisis. With their clothes, toys and even rooms decorated accordingly, it would be difficult to remain untouched by this social stereotyping that goes on in society throughout life. Society plays a role in initiating and perpetuating role-assignments of the genders, influencing decision-making and social behavior.

There are cases to support the nature versus nurture theory however, such as the infamous Joan/John case. In 1967, a twin boy had an accidental castration, and a medical decision was made, to raise the child as a girl with the help of surgery. For the next two decades, many sex reassignments were performed. Twenty-five years later, this medical success story came to haunt those same sexologists when Joan, though initially unaware of the facts could not adjust to the change and chose to return to her former sex (7).

Conclusion:

In a society where the exploration of innate variation is a topic of ethical controversy, it is only prudent to approach any data or discussion on gender difference very gingerly. Data interpreted to show genetic biases for differences among humans in intelligence, motor learning capabilities, criminality, and a broad range of other behaviors has, unfortunately, been used to support racism and other forms of bigotry (3). Because of such societal interpretations, scientists are becoming much more cautious of the conclusions they draw in an effort to avoid discriminatory sociological or political ramifications (13).

Throughout this entire semester, we have discussed the matter of brain equaling behavior. Quantifying exactly what behavior to expect from a man or a woman is an enigma, as we're talking about not just the anatomical variations one is born with, be it an XX sex chromosome or an XY, but also the changes that occur over one's lifespan. The brain is a structure that continues to evolve, be it because of the stages in development or stimuli/experiences of life. While the dominance of nurture over nature is no longer assumed yet the percentage of the effect that genetics and environment play on sexual identity is uncertain.

References

1) Gender Identity Disorder by Anne Vitale

2) The Role of Estrogen in Sexual Differentiation by Elaine Bonleon de Castro

3) Gender Differences in Cognitive Functioning by Heidi Weiman

4) Sex on the Brain - Biological Differences between Genders by Deborah Blum

5) Cognitive Development

6) Gender-Related Heart Differences in Human Neonates by Emese Nagy

7) Boys will be Boys: Challenging theories on Gender Permanence by Josh Greenberg

8) Neural Masculization and Feminization by Mary Bartek

9) Thinking about Brain Size

10) Gender Issues - Excerpt from "Reviving Ophelia" by Mary Pipher

11) Women's Brains - More Effective?

12) Speech Processing in the Brain

13) The Nature Versus Nurture Debate

14) The Genetic-Gender Gap

15) Explanations of Criminal Behavior


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