Hormones in Context:
Systems and Controls.
Estrogens and Androgens.
Testosterone and Aggression.
The role of aggression.
Mice and rats.
Flooded with testosterone?
Crimes of violence.
Clearly the motivation to fight is influenced by the situation. A male may fight another male that threatens his mate, or approaches one that he courting. A female might fight to protect her young when, at other times she might flee. Rats that were deprived of nourishment when very young were more likely to fight when they were older. In experiments where they were trained to press a bar to obtain food, they also continued much longer. However, since they were undernourished when suckling, by depriving the mother, she was affected, which meant that she was less attentive, and they interacted less with their peers.
In earlier chapters, we described how biologists are concentrating their attention on the extent to which learning influences behaviour. Even the behaviour of rats and mice is influenced by the sort of maternal care they receive. It has been suggested that, when newborn rats have their hormones tinkered with, the difference in their smell may well affect maternal care. In addition, a study has demonstrated that the general behavioural characteristics of the mother can have an effect.
Laboratory rats and mice can be selected for specific physiological or behavioural characteristics. In one study,(1) there were two strains. One exhibited a generally low level of aggression, measured on the frequency of chasing, attacking and fighting. The other strain exhibited high levels under the same conditions.
When a low aggression female was mated to a high aggression male, the male offspring consistently had a low aggression score. When a low aggression male was mated to a high aggression female the opposite result was obtained. In other words, the mother's 'personality' had a significant effect on the offspring.
This could, of course, have been a genetic effect of the mother's X chromosome, or prenatal hormonal effects. However, the experiment was repeated by cross-fostering the young. Thus the male offspring of parents that were both from the high aggression strain, were fostered by a low aggression mother. The offspring displayed a significantly lower level of aggression than those that stayed with their original mother, and vice versa. It would seem, then, that a significant effect arose from the way the mother treated the young after they were born.
Similar studies were carried out with other species, including rhesus monkeys. Mitchell and Brandt concluded that mothers encourage greater independence and activity in males. Mothers of males act as "punishers", of females as "protectors". Young males are "doers"; young females are "watchers."(2)
There is no ethical way that one can carry out experiments on human beings. However, the side effects of various drugs used to help women in pregnancy is said to support the idea that prenatal hormones affect the personality of the child. A problem for women with diabetes is that they often suffer spontaneous abortions. For a while this effect was countered by treating the mothers with a hormone, diethylstilbestrol. Later, it was discovered that little boys, born to these mothers, were much less assertive as they grew up. For a while, too, male hormone had been administered to mothers with toxemia and, again, if the child was a girl, she was said to show measurable behavioural differences.
However, in such studies, no account was taken of the effect on the mother after the birth, or her emotional state. In some cases the mother's condition was severe enough to require daily attention. Were mothers' behaviours different towards their offspring? In other cases, the baby had genital abnormalities. What effect did these have on the children's view of themselves? Once again, there were several studies and the results were, by no means, as straightforward as is sometimes suggested.
Fausto-Sterling(3) is clear that "The claim that clear-cut evidence exists to show that fetal hormones make boys more active, aggressive or athletic than girls is little more than fancy, although harmless it is not."
The effects of socialisation on animals, even rats and mice, is considerable. Some time ago, experiments were carried out on young Rhesus monkeys that might now be considered unethical. One group was brought up from birth with an artificial 'mother' made out of cloth, without any living companions.
When introduced into the community, they exhibited behavioural problems, ranging from hyperaggression to withdrawal, with sexual and parental incompetence, along with other social disorders.
A second group had real mothers but no age peers. They also exhibited hyperaggression. They were extremely mother-dependent, although they were more willing to explore.
In other studies, Rhesus monkeys developed within a normal social structure, but lived in what is known as a restricted environment. This was bare and monotonous with little to stimulate the senses, rather like an inner city housing estate. The monkeys were more gregarious but, at the same time, more aggressive, and there was less social grooming
Next Page: Flooded with testosterone?
Bibliography and good reading.
Bland, J.,(2002) About Gender: Testosterone and Aggression - Mothers.
Book graphics courtesy of Amazon.co.uk
Web page copyright Derby TV/TS Group. Text copyright Jed Bland.
06.05.98 Last amended 12.03.02