Chromosomes
Chromosomes are comprised of genes which in turn are strands of DNA:
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Humans have 23 pairs of chromosomes, the 23rd pair being the sex chromosomes. XX Female Therefore the ovum always contains an X. A sperm can contain an X or a Y. Sex of offspring is therefore decided by the male. |
The Y chromosome contains the Sex-determining Region (SRY). It’s the SRY that results in the development of testes in babies in XY (male) babies. Once developed, the testes then secrete androgens (male sex hormones) such as testosterone that results in the development of a male. Clearly, women who have no Y chromosome have no SRY so remain female.
Note: there are a few very rare exceptions to this rule. These are discussed when we look at atypical chromosome patterns.
Research support
The case of David Reimer offers support for the power of chromosomes in determining not only our sex but also our gender. David, born Bruce, was brought up as a girl (Brenda) after a botched circumcision resulted in the destruction of his penis. Despite being brought up as a girl, Brenda never felt feminine. Despite the best (and worst) attempts of psychologist John Money to convert David into a girl he never accepted his femininity. In later life he did convert back to being a man. This would appear to support the power of biology over socialisation and nature over nurture in the development of gender.
Hormones
Hormones play essential roles in sex development and have particularly powerful effects at two key points in our development.
In the womb it is sex hormones that determine the development of primary sex characteristics. Presence of SRY causes testes to develop that then secrete testosterone and other male hormones. These cause the development of male genitalia. (See the case of the Batista Boys).
At puberty another release of hormones produces the secondary sex characteristics associated with this stage of life. Testosterone in boys leads to deepening of the voice and male patterns of body hair. Oestrogen in girls causes breast development and triggers the menstrual cycle.
Testosterone
Although the testes develop in the womb, it’s not until they start producing sex hormones like testosterone that development into a male begins. In particular testosterone is responsible for development of the epididymis and vas deferens. Later it will also be instrumental in descending of the testes into the scrotal sac. As well as testosterone two other crucial androgens are produced by the testes: anti-müllerian hormone (AMH), and dihydrotestosterone (DHT). See the story of the Batista Family below.
Oestrogen
The main female sex hormone, secreted by the ovaries, it determines the secondary female sex characteristics and menstruation. It is also plays a role in the fluctuating moods experienced during the menstrual cycle. When experienced at the extreme these symptoms can be diagnosed as PMS (pre-menstrual syndrome). Many however, question the validity of this diagnosis, whilst others object to the concept of labelling women as somehow odd because they experience changeable moods. Here we have a perfect example of research that labels women as odd because they have an experience different to men. We looked at this in the topic of gender bias. If men have emotions and feel anger there will be a logical, situational explanation. Similar symptoms in women must be due to their different biology. Beta bias in the form of androcentricism.
Oxytocin
Oxytocin is the love hormone (pronounced lurrrvve obviously J). Although men produce small amounts, women produce it in much greater quantities, particularly after giving birth. It appears to facilitate bonding and breast feeding. During child birth large amounts are secreted by the hypothalamus and is thought to create the very close and intimate mother-child bond. Again we have a possible example of beta bias. It is thought to be responsible for the nurturing nature of women (see what I did there?) so again explaining away women’s behaviour in terms of their biology.
Already said this, but men do produce small amounts and in fact during intimate acts such as kissing and intercourse produce just as much as women.
Research support for hormones
Transgender (male to female) patients who are receiving injections of female sex hormones show less aggression, whereas female to male who are receiving injections of testosterone become more aggressive. This does seem to suggest a casual role of hormones on sex-typed behaviour.
Dabbs et al (1995) found that men imprisoned for violent and sexual assaults generally had higher levels of testosterone.
However, Tricker, in a double blind study, compared two groups who were either receiving weekly injections of testosterone or a placebo. No significant difference in levels of aggression was reported.
Overall
As always the biological model offers an overly-simplistic model of gender determination. It fails to consider differences in the way the two genders appear to think (best explained using the cognitive models). Similarly it doesn’t consider the vital role played by parents, media and culture. Maccoby & Jacklin (1974), as we’ve already seen, believed there only to be four genuine sex differences. If biology was so important surely we’d expect to find more.
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The Batista Boys
There is a family in the Dominican Republic that highlight the importance of the presence or absence of testosterone. They are rare. In fact there are only known to be 23 families in the World that have this condition.Their rare genetic disorder occurs because of a missing enzyme which prevents the production of a specific form of the male sex hormone – dihydro-testosterone – in the womb. All babies in the womb, whether male or female, have internal glands known as gonads and a small bump between their legs called a tubercle. At around eight weeks, male babies who carry the Y chromosome start to produce dihydro-testosterone in large amounts, which turns the tubercle into a penis. For females, the tubercle becomes a clitoris. But some male babies are missing the enzyme 5-α-reductase which triggers the hormone surge, so they appear to be born female with no testes and what appears to be a vagina. It is not until puberty, when another huge surge of testosterone is produced, that the male reproductive organs emerge. What should have happened in the womb happens around 12 years later. Their voices deepen and they finally grow a penis. They are brought up as girls for twelve years before emerging as boys at puberty. |
Atypical patterns of sex chromosomesClearly the norm as far as sex chromosomes is concerned is either XX or XY. However, in rare circumstances other patterns do occur and can have dramatic effects.
Klinefelter’s Syndrome (XXY)
This is the result of one such abnormal chromosome pattern. It occurs in only 1% of the population, although this figure could be higher since most patients are unaware of their condition.
The pattern is XXY and the person appears male.
Physically the person tends to have reduced body hair and more feminine secondary sex characteristics such as more rounded hips and addition sub-cutaneous fat. There may also be some breast development (gynecomastia) at puberty. Legs are often longer and there may also be less well-developed sex organs.
Presumably, because of the additional breast development, breast cancer is more likely in patients suffering from Klinefelters.
Psychologically and behaviourally, patients are more likely to be clumsy, have poorer language skills, especially reading, be more passive, shy and less able to cope with stress.
Turner’s Syndrome (XO)
Even rarer than Klinefelter’s, Turner’s Syndrome is believed to only affect I in every 2000 girls. It is caused by a missing X chromosome, hence the designation XO. Turner’s patients only have 45 chromosomes rather than the usual 46. As a result the ovaries fail to fully develop and patients are unable to have children.
Physical characteristics include amenorrhoea (cessation of periods) as often seen with anorexia. Their overall appearance remains pre-pubescent. The lack of ovaries and therefore oestrogen and progesterone results in lack of secondary sex characteristics such as breasts, and lower waist to hip ratio. In addition there may be webbing of the neck, and low-set ears.
Psychologically and behaviourally, patients have above average language skills, especially reading, but tend to be less able than average at maths. Socially they tend to be immature.
Evaluation
Nature versus Nurture
As always when things go wrong with brains and bodies psychologists can learn a lot about a whole range of issues. In these particular cases, the fact that language ability has been affected by a chromosomal abnormality would seem to suggest our biology plays a role in this ability, rather than just the way we are educated. It suggests, controversially, that genes can have a direct influence on intelligence. Perhaps the most controversial in the history of psychology!
However, as always, we have issues with cause and effect. Both conditions affect a whole range of physical and psychological factors and many of these characteristics might be having indirect consequences for others. An example will help me explain.
The immaturity, particularly in relation to peers and in social situations might be due to their immature appearance. Because they look pre-pubescent, there may be a tendency for people to treat them as though they’re much younger. In which case they may not develop more adult social-niceties. Think how we often speak to young people and how that differs to the way we treat older people.
Similarly, teachers may well have lower expectations of them because of their youthful appearance. Lower expectations can be a self-fulfilling prophecy.
Following on from this argument: drawing conclusions about the causation of psychological functions from such an atypical group is clearly troublesome.
Additionally, only one third of Klinefelter’s patients appear to be aware of their condition and therefore known to the medical profession. It seems fair to assume that the ones we are aware of are not typical of Klinefelter’s patients as a whole. It’s likely that those aware of their condition have the more severe symptoms. Those unaware are likely to have milder symptoms resulting in fewer noticeable issues. As a result, the patients being studied are not even typical of the condition.
Practical Applications
Greater awareness of these conditions and of the problems that can arise, has resulted in earlier diagnosis, which in turn can result in better long term outcomes. An Australian study of 87 patients with Klinefelter’s Syndrome showed that earlier intervention had significant benefits for the patients.
CGS Psychology Blog: Mrs Harris 