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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.

However, since the social argument points out that humans behave in much more complex ways than rats, research switched to various species of apes and monkeys. Various experiments, injecting male hormone into female rhesus monkeys at different stages of development produced different sexual and aggressive behaviours.

An experiment with female talapoin monkeys injected them with hormones so that they all had the same circulating level. Only the dominant female made any attempt to interest a male, exclusively directing her interest at the dominant male, with his attention directed exclusively at her. In many species of monkey, the dominance relationships that existed before castration, continue afterwards.

Whatever effects sex hormones have, in organising effect prenatally, and later stimulating behaviour,. they are greatly reduced in species which have a social organisation. They may have an effect on what a creature is ready to do, but what it actually does, depends on the situation, and with an even more complex social organisation, the situational variables for humans are much greater.

The individual developmental history has also to be taken into account since experience of the animal, even of mice and rats, particularly of fighting, also has an effect. In groups which have a social dominance structure, the highest ranking male may fight only rarely. While a given male may be considered the most aggressive because he has the most access to resources, those successful at fighting tend to be high ranking. At this point, the experiential effect occurs. The testosterone level tends to be high, but winning a fight tends to raise it, while losing causes it to fall.

Thus hormone levels become the result rather than the cause of fighting and, in some species, a low level inhibits the sexual abilities of the low ranking members. But, in any case, animals learn about winning or losing. If their first fights as adults are successful, they will fight in different way than if they were unsuccessful.

Chimpanzees in the wild rarely come to blows, or there is no serious violence, at least within the group. The group hierarchy is derived by complex socialisation, mutual grooming, a placatory caress and, on the other hand, daunting power displays, with males crashing around in the undergrowth. Often a subordinate male will form a coalition with one or two others to oust a senior male.

Chimpanzee aggression is channelled through politics. Symons(1) suggests that, in the beginning, the evolution of human intelligence was encouraged by similar, or more complex, social interactions. However, his suggestion that the evolution of human intelligence, derived from male sexuality, with the implication that females got it by default, has not been received well by feminists.

Jane Goodall(2) carried out a thirty-five year longitudinal study of chimpanzees of Gombe National Park in Tanzania. In the process, she found that many assumptions about their behaviour were simply not true. She, and her assistants, studied several families in a group, learning to recognise each individual by sight. For convenience each of the offspring in the matriarchal line were given names with the same initial letter. It is easy to anthropomorphise in such situations - to assign to animals human emotions and personalities - but the complexity of their behaviour made it necessary to describe it in humanly understood language.

A television programme(3) focused specifically on a female, Flo and two of her sons, Freud and Frodo. Freud was the oldest of the two brothers. He was very laid back, and had taken over as alpha (senior) male with very little fuss. Even when younger, he had been very gentle and passive. There was no hint he would become the leader. Yet, when he did feel it necessary to assert his authority, by a threat display, even his brother would find a nearby tree.

His younger brother, Frodo was much bigger and stronger, large even by chimpanzee standards, and brash. Most of his play sessions as a youngster ended with him bullying the others. Perhaps the other males remembered. Perhaps they mistrusted his slightly erratic nature, but he had never managed to form a coalition of other males, and could not face his older brother down, even though he was bigger and probably stronger

The researchers were sure that Freud's quiet confidence was the key - size wasn't everything. His confidence was such that he could quietly disappear for a few hours to spend time alone, without worrying about what the other males might be doing.

Next Page: Mothers.

Bibliography and good reading.

  1. Symons, D., (1979) The Evolution of Human Sexuality, New York: Oxford University Press (bookshelf)
  2. Goodall, J., (1986) The Chimpanzees of Gombe, London: Harvard University Press. (bookshelf)
  3. Fifi's Boys: A Story About Wild Chimpanzees, BBC Television (The Natural World), 4th. February, 1996
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Bland, J.,(2002) About Gender: Testosterone and Aggression - Primates.
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Web page copyright Derby TV/TS Group. Text copyright Jed Bland.
06.05.98 Last amended 12.03.02