Although the neural mechanisms involved in ageing have not been widely researched, it has been suggested that they could involve the same neural circuitry as that which is affected by hormones. A region of the suprachiasmatic nucleus, involved in the control of circadian rhythms which affect sleep patterns, contains twice as many neurons in men as in women until middle age, when the sex difference reverses and then ultimately disappears. Women live longer than men but only by an average of about four years, though the oldest person to have lived was a woman aged 125 while the oldest man was ten years younger at 115.
Changes in gene expression occur during ageing of the brain, affecting more than three times as many genes in men than in women. Women and men have equivalent numbers of up-regulated (more active) and down-regulated (less active) genes. In men there are reductions in volume in regions of the brain which are greater than those in women, especially in frontal and temporal lobes but also in whole brain volume. Brain volume reductions might lead to less ability to carry out particular tasks in men than in women. Women tend to show stronger reductions than men in the hippocampus and parietal lobe, possibly leading to more deficits in memory functions. But women still have better memories than men regardless of age. In both men and women the sex drive declines with age. This happens more quickly in the case of women, though their desire for sex does not seem to go altogether. The effects of the menopause are important, especially with the loss of sensitivity in the genital area that tends to occur at that time.
All of these examples go to show that sex differences in health and illness are significant.
13
Differences
Well, there’s a little bit of man in every woman and a little bit of woman in every man.
Betty Smith
When I started this book I already knew that the differences between men and women were a hotly disputed area. There were many ingrained myths, for which the evidence is very poor, such as women being less intelligent than men or speaking much more than men, and some trivial myths for which the evidence is quite good, such as men being better at map-reading and women poorer at parallel parking. There are many contrasting theories on the origin of differences and whether they came from biological or social causes. I knew little about the differences in emotions, skills and brain structures. But having studied the evidence I am persuaded that there are significant biological differences that affect how the two sexes behave. Further research, though, is required to understand the neural basis of these differences.
Humans are very complex, their brains and social life especially so, and so clear results from research are not easy to come by. The evidence, however, is persuasive that there are some fundamental biological differences between men and women. Intellectual differences are small, but differences in emotions are more significant, as are the physical and physiological differences that arise during development of the embryo and which have the most profound effect.
These differences can be best understood in terms of Darwinian evolution, as they have made the two sexes better adapted to their environment and also, by having two sexes at all, have generated more variants for selection to act on. In spite of the importance of evolution in determining differences between males and females, it is often totally neglected in studies that deny the role of biologically based differences. It could even help male–female relationships if the fundamental biological differences between men and women were more widely understood and appreciated.
Evolution has resulted in men being modified women. The early development of the human embryo is similar in males and females, and is essentially female, with sexual differences appearing only at later stages. The default development of the embryo is female, and testosterone, together with some genes, plays a key role in causing male development, both in body and brain, so males are essentially modified females and that is why they have functionless breasts. Evolution cares only about reproduction and the survival of offspring and it has been crucial in determining the biological differences between men and women. Men were modified to fulfil tasks requiring speed and strength, like hunting and protection, and so in development grew to be significantly bigger and stronger than women. They are also more aggressive, and this can be a physical and social advantage enabling men to dominate women. Women can be aggressive too, but their aggression is rarely physical. Men are also more likely to take physical risks. These physical male advantages, together with women bearing and caring for children, are the main reasons why women have been discriminated against and subordinated for a very long time. The nature of sexual attraction today may still have echoes from our evolutionary past as signs of good health and a symmetrical body that is neither too fat nor too thin are considered important female characteristics in developed cultures.
Unlike men, women were selected to be loving carers for their children and this resulted in them having much stronger feelings of empathy. Women thus have an ability to share other people’s feelings, to have a positive interest in other humans, and to excel in the ability to decode non-verbal emotional cues which plays an essential role in child care. When viewing sad humans they show enhanced brain activity in brain regions believed to be part of a mirror neuron system which supports empathy. Women are more emotional than men, show their emotions more and have better recall of emotional memories. They cry and smile more than men.
Men have less empathy than women and have evolved to be systemisers. Systemising is the intuitive ability and drive to analyse and construct systems which follow rules, and these systems often explore areas which are more abstract and not directly related to other humans. These differences between an empathetic brain and a systemising one can make male–female relationships a bit difficult at times.
Clear sex differences with a biological basis can be seen in the behaviour of children from a very early age and show the early expression of empathy and systemising. Newborn girls spend more time looking at faces, while boys are more interested in things like mechanical mobiles hung from the ceiling. Sex-typed toy preferences, such as boys preferring trains and cars, and girls preferring dolls, and other sex-typed differences in children’s play and conversation would seem to be biologically determined and influenced by testosterone in the womb. However, social influences, such as how babies and children are treated by their parents, can play a role.
We know that there are genetically specified differences in male and female brains that can affect their behaviour, but there is still much to be learned. Development results in the adult male brain being ten per cent larger than the female brain. Females tend to have more localised regions of information-processing grey matter and more networking white matter relative to brain size than males, which may explain some intellectual differences. Although there is no difference in intelligence, males vary more widely in certain abilities–there are more males with both high and low scores when tested for maths–while women tend to be better at assimilating and integrating information, and at remembering it.
Several structures related to sexual behaviour are different in men and women, and there are also reports of structural differences in various other regions whose function remains to be further investigated. While significant brain differences are mainly due to development in the embryo, social factors must also play a role.
Reproduction is at the core of male–female differences. The evolutionary advantage of having two sexes is complex but probably depends on generating more differences in the offspring produced, so that only those that are best adapted are selected. The desire for children and hence for sex are genetically determined emotions in both men and women and were programmed into our genes in the course of evolution. A fundamental biological difference is that men are much more sexually motivated than women. Both during tactile genital stimulation and when viewing the same sexually arousing visual stimuli, the differences in brain activity are particularly marked. Male sexual orientation is based upon the direct effect of testosterone on the developi
ng human brain, as shown by genetic disorders that prevent cells responding to testosterone. CAH causes excess testosterone in the womb and leads to an increased incidence of homosexual feelings in women, although most CAH women are heterosexual. Male homosexuality is influenced, surprisingly, by how many older brothers a male has.
There are numerous differences between men and women in their susceptibility to certain illnesses. Bearing children, with months of pregnancy and years of caring for offspring, has had far-reaching effects. Women’s health in relation to infections was crucial and they evolved a very strong immune system which can unfortunately overact and cause autoimmune illnesses like multiple sclerosis. Women are more prone to suffer from chronic diseases such as depression and arthritis, while men are more likely to suffer cardiovascular disease, stroke and autism. These are clear examples of genetic origin.
There are no major intellectual differences between men and women. Possibly related to systemising is the major and well-established difference that men score higher than women on tests of mental rotation and on tests of spatial perception and orientation. Male hormones play a key role, and females with CAH have higher spatial ability than their sisters throughout life. Women generally score higher than men on memory tests based on finding objects in spatial displays. They can even recall objects that have been added, or have changed places, making them more efficient shoppers in a supermarket. Females have also been found to excel at landmark memory, that is, memory of images of differing types of structures. They are also better with episodic memory, that is long-term memory based on personal experiences, and with short-term memory.
The almost universal subjection of women by men is hard to explain in terms of the differences in the emotions and skills that I have discussed, but empathy possibly makes women more willing to do what men request. Much more significant is the greater physical strength and aggression of men, and the burden on women of childbirth and the bringing up of children, which have been genetically imposed.
A recent report by the European Union Agency for Fundamental Rights showed that in Europe one-third of women have been victims of violence and in Britain even more. In a different study it was found that more than half of women in Britain have experienced bullying or harassment at work in the past three years
Women do not talk more than men, but what they say can be very different. The difference between men and women in relation to language is either small or close to zero. Differences in language use thus probably have a strong social cause, although biological factors like empathy are also involved.
The absence of women from fields related to maths and technology is largely due to social and biological factors that result in them preferring not to work in these areas and their having to look after children, not to their abilities. It could also be that their greater empathy attracts them less to these subjects, or that they are discouraged by strong negative stereotypes of women being unsuitable to work in these fields. Better early education of girls would help to overcome these stereotypes and give them more confidence about entering such fields. It is important to get rid of negative female stereotypes in relation to maths, science and engineering, and there must be greater effort to support the care of children. There is evidence that women can do well in engineering if they are linked with similar colleagues and have the necessary training. This is a set of objectives to be strongly encouraged. It is also necessary to get rid of prejudice, as a recent study in the United States found that both male and female researchers tend to rate job applications from women for a post in science lower than those from equivalent men.
In an article by Kay and Shipman about their new book The Confidence Code, they claim that there is ‘a vast confidence gap that separates the sexes. Compared with men, women don’t consider themselves as ready for promotions, they predict they’ll do worse on tests, and they generally underestimate their abilities. This disparity stems from factors ranging from upbringing to biology . . . The good news is that with work, confidence can be acquired. Which means that the confidence gap, in turn, can be closed.’
There is no doubt that biology, via evolution and genetics, has made men and women significantly different. But where skills are concerned, there are not so many differences between the sexes and serious efforts must be made to make this widely known, and for women to be urged to enter a wider variety of fields.
*
In writing this book, I have learned a good deal about myself and a great deal about women. For example, I knew virtually nothing about empathy. I try now to see if I really do lack empathy and make an effort to use it in relation to my family. But there is no good evidence that I am succeeding. I am a classic systemising male, after all.
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