Biology of gender

The biology of gender is scientific analysis of the physical basis for behavioural differences between men and women. It is more specific than sexual dimorphism, which covers physical and behavioural differences between males and females of any sexually reproducing species, or sexual differentiation, where physical and behavioural differences between men and women are described.

Biological research of gender has explored such areas as: intersex physicalities, gender identity, gender roles and sexual preference. Late twentieth century study focussed on hormonal aspects of the biology of gender. With the successful mapping of the human genome, early twenty-first century research started making progress in understanding the effects of gene regulation on the human brain.

History
It has long been known that there are correlations between the biological sex of animals and their behaviour. It has also long been known that human behaviour is influenced by the brain.

The late twentieth century saw an explosion in technology capable of aiding sex research. John Money and Milton Diamond made great progress towards understanding the formation of gender identity in humans. Extensive advances were also made in understanding sexual dimorphism in other animals. For example, there were studies on the effects of sex hormones on rats. The early twenty first century started producing even more amazing results concerning genetically programmed sexual dimorphism in rat brains, prior even to the influence of hormones on development. "Genes on the sex chromosomes can directly influence sexual dimorphism in cognition and behaviour, independent of the action of sex steroids."

Brain
The brains of many animals, including humans, are significantly different for males and females of the species. Both genes and hormones affect the formation of many animal brains before "birth" (or hatching), and also behaviour of adult individuals. Hormones significantly affect human brain formation, and also brain development at puberty. Both kinds of brain difference affect male and female behaviour.

In 2006, Alexandra M. Lopes and others published that: A sexual dimorphism in levels of expression in brain tissue was observed by quantitative real-time PCR, with females presenting an up to 2-fold excess in the abundance of PCDH11X transcripts. We relate these findings to sexually dimorphic traits in the human brain. Interestingly, PCDH11X/Y gene pair is unique to Homo sapiens, since the X-linked gene was transposed to the Y chromosome after the human–chimpanzee lineages split.

Although men have a larger brain size, even when adjusted for body mass, there is no definite indication that men are more intelligent than women. In contrast, women have a higher density of neurons in certain parts of the brain. However, difference is seen in the ability to perform certain tasks. On average women are superior on various measures of verbal ability, while men have specific abilities on measures of mathematical and spatial ability.

Richard J. Haier and colleagues at the universities of New Mexico and California (Irvine) found, using brain mapping, that men have more than six times the amount of gray matter related to general intelligence than women, and women have nearly ten times the amount of white matter related to intelligence than men (Haier, Rex E Jung and others, 'Structural Brain Variation and General Intelligence', NeuroImage 23 (2004): 425–433). "These findings suggest that human evolution has created two different types of brains designed for equally intelligent behavior," according to Haier. Gray matter is used for information processing, while white matter consists of the connections between processing centers.

Aptitude
A 2001 report by Richard J. Coley of the ETS found that females often outperformed males on various measures of verbal ability, while males tended to outperform females on measures of mathematical and spatial ability. 

Studies have shown that men show a greater variance in scores than females. The average scores of young men and women in mathematics, for example, will be close, but there will be more men than women in the very low scores and in the very high scores. In this sense, the red bell curve in the diagram represents women, compared to men in green. There is evidence to suggest that forms of autism may be essentially extreme expressions of certain typically male characteristics. This is represented by the blue in the diagram.

Behavior
Hormones have been linked with male aggression.

For an illustrated description of clear differences between male and female brain response to pain see Laura Stanton and Brenna Maloney, 'The Perception of Pain', Washington Post, 19 December 2006.

Nature or nurture
There is a lot of variation in men and women that is not yet understood. It cannot be proven that male-ness or female-ness is 100% biological (in fact virtually all studies show that it is not). However, it is also probably true that male-ness and female-ness are not 100% determined by upbringing and culture (social determinism). These issues remain an area of ongoing research, with profound relevance for people of many different types. One journal (Genes, Brains and Behavior) is devoted specifically to research in this area.

Research motives
Most biological research is motivated by seeking the causes of diseases in human beings, and ways of treating or preventing those diseases. For example, there is study into genetic predisposition to, or causes of, Alzheimer's disease and mental illnesses. Also: Scientists have cracked the code of an essential signal in the sequence of steps that controls the molecular choreography of gene regulation. The discovery is expected to aid development of therapies and prevention strategies for certain genetically triggered diseases such as breast cancers, pediatric cancers, and leukemia.

Patriarchy
Most societies in recorded history have been arguably patriarchal. Some people believe things like patriarchy and sexual differentiation are not only inevitable but constructive. However, many others consider them destructive and want to eliminate them. Also, it can and has been argued that "patriarchy is not a universal feature of human societies."

Ethics
Even if it was possible to remove partriarchal behaviour by an injection, there are ethical questions that need answers before any such procedure could be performed:
 * Should it be made law for such an injection to be given?
 * Should parents be given the choice, or only mothers?

Literature

 * Baron-Cohen, Simon. The Essential Difference: The Truth about the Male and Female Brain. New York: Perseus Books Group, 2003.
 * Brizendine, Louann. The Female Brain. New York: Morgan Road Books, 2006.
 * Brown, Donald E. Human Universals. New York: McGraw Hill, 1991.
 * Kimura, Doreen. Sex and Cognition. MIT Press, 1999.
 * Moir, Anne and David Jessel. Brain Sex: The Real Difference Between Men and Women.
 * Pinker, Steven. The Blank Slate: A Modern Denial of Human Nature. London: Penguin Books, 2002.

Journals

 * Genes, Brains and Behavior