[under construction]… are they different? … how different are they? … what about political correctness?
If we separate humans into the two genders male and female, and measure all kinds of things, physically and psychologically, we find that, on average, some traits differ between the genders. This is clearly not rocket science – we see evidence of that daily when we notice that, on average, men are taller than women, have more body and facial hair, and smaller breasts.
If a trait is stronger in women, it may be called feminine; if it’s stronger in men, it may be called masculine. This is simply how language works, there is no discrimination or value judgement implied. Such classification also does not mean that all women have a particular feminine trait, or that this trait is stronger in every single woman than it is in every single man. It doesn’t even mean there is a large difference between the genders, or that there is only a small or no overlap between the genders. It simply means a significant difference can be observed. Such classification also makes no statement about cause, only about correlation. If a psychological difference is observed, the root may be social, cultural, physiological, etc., or a mixture of many factors.
Normal distribution is a commonly occurring probability distribution. In nature and social sciences, observations very often cluster around an average, and outliers (observations that differ strongly from the average) are rare. Examples for such distributions are people’s height or intelligence. Average height for humans might be around 1.75 m, and many people are close to this average. People who are very short or very tall are rare. It’s the same for intelligence – the average IQ is 100, and most people are between 80 and 120. People with very high or very low intelligence are rare.
An interesting article regarding sex differences in the brain is “Sex Differences in the Brain: The Not So Inconvenient Truth” by Margaret M. McCarthy, Arthur P. Arnold, Gregory F. Ball, Jeffrey D. Blaustein and Geert. J. De Vries, published in “The Journal of Neuroscience”, 2012. The article states that “there are pervasive sex differences in the brain”, “there are important sex differences in cogntitive and emotional responses relevant to learning and memory, language, fear, anxiety and nociception”, and argues for more research into such differences. It also lays out ways on how brain sex differences can be attributed to their respective causes, such as genetic effects, hormonal effects before and around birth or hormonal effects in adulthood.
To bring clarity into the definitions of gender differences, the article by McCarthy et al. operationally defines the following three categories (remember, we are usually talking about averages on a spectrum of possibilites):
My website deals with selected aspects of transsexualism, and gender differences are not an area I cover, or specialise in. However, many of the articles I have collected, do touch on gender differences, for example in brain development. To give just two quick examples of psychological gender differences, have a look at these two scientific studies: “Gender Differences in Personality across the Ten Aspects of the Big Five” and “The Distance Between Mars and Venus: Measuring Global Sex Differences in Personality”.
Findings from these studies include: “Replicating previous findings, women reported higher Big Five Extraversion, Agreeableness, and Neuroticism scores than men” and “[…] the largest differences between the sexes were found in Sensitivity, Warmth, and Apprehension (higher in females), and Emotional stability, Dominance, Rule-consciousness, and Vigilance (higher in males)”.
Based on the evidence provided, it seems that there are psychological differences between men and women. Please note that these studies do not cover causes of sex differences, so we can not tell from them whether they are socially caused or biologically innate.
When we look at female and male humans, we do see a difference. It would be very surprising if this difference was limited to secondary sexual characteristics, to the genitals, and the reproductive organs. As one would expect, the sex differences also extend to the brain, our biggest sex organ. And since the brain produces our identity and makes us what we are, differences in the brain can lead to differences in personality and behaviour. The other way around is also true – differences in personality and behaviour can also be tracked to brain structure and function.
The question about why men and women are different, and whether this difference is biologically innate or simply the product of culture and society, used to be simply put as the “nature-versus-nurture” debate. One of the extreme hypotheses relating to this debate is the “blank-slate” theory, which states that men and women are psychologically identical at birth – all differences are created socially, by society raising and treating the genders differently. This hypothesis has long been discredited, not only by the daily lived experience of transsexuals, but also by dramatic cases such as the tragic John/Joan case.
Additionally, animal observations and experiments as well as studies on human new-borns who haven’t been socially influenced and on twins can inform us about innate sex differences. There are many such studies (some can be found on the reference pages on brain development). As an example, gender differences in play and social behaviours in humans also been found in many other animals. This goes so far to include gender-specific toy preferences – male monkeys show strong preferences for wheeled toys, while female monkeys prefer plush toys. Psychologist Gerianne Alexander states on these findings in the New Scientist that “there is likely to be a biological tendency that is amplified by society”.
Many of these sex differences can be linked back to the actions of sex hormones before birth. They act during the early developmental phase of the brain, which can have permanent effects. However, developmental and psychological issues tend to be very complex, and sexual dimorphic behaviours are certainly shaped by a great multitude of factors, including hormonal, genetic, epigenetic, environmental, social and cultural influences. Many, many factors contribute to shaping us into the person we are. The result is always an unique individual, a person special in many ways, and this also means different in many ways – a fact we should celebrate!
 Some quotes from McCarthy at al. about the causes of brain sex differences: “It is likely that the majority of sex differences in the brain are caused by gonadal hormones, acting in the adult (different effects of ovarian and testicular hormones) or early in development (especially effects of testicular hormones).”; “The importance of early life programming pervades all of neuroscience but is perhaps best exemplified in the profound impact of hormones on the developing brain to ‘organize' or ‘program' the brain as male or female across the life span.”
 “Gender Differences in Personality across the Ten Aspects of the Big Five” by Y. J. Weisberg, C. G. Deyoung and J. B.Hirsh in “Frontiers in psychology”, 2011.
 “The Distance Between Mars and Venus: Measuring Global Sex Differences in Personality” by Marco Del Giudice, Tom Booth and Paul Irwing in “PLoS One”, 2012.
 The John/Joan case in brief: After a botched circumcision, the penis of a baby boy was removed and sex change surgery performed. This was due to the belief of the psychologist John Money in the blank-slate theory, thinking that the child would be better off raised as a girl. During adolescence, however, the patient transitioned to live as a male and later went public to prevent similar medical practices. After suffering years of severe depression, he committed suicide. The case was made worse by John Money actually publishing the case as successful and as evidence that gender identity is primarily learned. It took the research of Milton Diamond to discover the truth.
 “Studies over the last 50 years have verified that prenatal androgens have permanent effects in rhesus monkeys on the neural circuits that underlie sexually dimorphic behaviors. These behaviors include both sexual and social behaviors, all of which are also influenced by social experience. Many juvenile behaviors such as play, mounting, and vocal behaviors are masculinized and/or defeminized, and aspects of adult sexual behavior are both masculinized (e.g. approaches, sex contacts, and mounts) and defeminized (e.g. sexual solicits).” – “Effects of prenatal androgens on rhesus monkeys: a model system to explore the organizational hypothesis in primates” by J. Thornton, J. L. Zehr and M. D. Loose in “Hormones and behavior”, 2009.
 “Male monkeys, like boys, showed consistent and strong preferences for wheeled toys, while female monkeys, like girls, showed greater variability in preferences. Thus, the magnitude of preference for wheeled over plush toys differed significantly between males and females. The similarities to human findings demonstrate that such preferences can develop without explicit gendered socialization. We offer the hypothesis that toy preferences reflect hormonally influenced behavioral and cognitive biases which are sculpted by social processes into the sex differences seen in monkeys and humans.” – “Sex differences in rhesus monkey toy preferences parallel those of children” by Janice M. Hassett, Erin R. Siebert and Kim Wallen in “Hormones and Behavior”, 2008.
 “Sex differences in response to children's toys in nonhuman primates (Cercopithecus aethiops sabaeus)” by Gerianne M. Alexander and Melissa Hines in the “Evolution & Human Behavior”, published 2002. “Sex differences in Infant’s Visual Interest in Toys” by Gerianne M. Alexander, Teresa Wilcox and Rebecca Woods in “Archives of Sexual Behaviour”, published 2009.
 “Male monkeys prefer boys’ toys” by Ewen Callaway in the “New Scientist”, published on 2008-04-04.
 “Early Androgens Are Related to Childhood Sex-Typed Toy Preferences” by Shetri A. Berenbaum and Melissa Hines in “Psychological Science”, published 1992.
 “Sex differences in chimpanzees’ use of sticks as play objects resemble those of children” by Sonya M. Kahlenberg and Richard W. Wrangham in “Current Biology”, published 2010.