Hormones are the body’s chemical messengers. In collaboration with the nervous system, the glands that produceensure that the various organs function in harmony with one another. Nerves work quickly but usually for only a short time. Hormones take effect more slowly but their action is of much longer duration. Many of the effects of hormones are not yet known. A great deal of research is being done, especially on their function in the brain. From experiments with animals, for example, it has been discovered that a number of hormones can affect the learning function; , a hormone that plays a part in childbirth and breast feeding, is believed to have a negative influence on the ability to learn, whereas vasopressin, which plays a part in, for example, regulating the amount of water in the body, is believed to have a positive influence on learning. The significance of this discovery for humans has not yet been fully established. From other data too, it is clear that hormones have a large influence on behaviour. Whereas an excessive production of thyroid hormones, for example, makes a person feel agitated and irritable, a deficiency results in listlessness. Protracted treatment with large quantities of adrenocortical hormones can give rise to mental disorders.
A subject which always gives rise to heated debate is the difference between the behaviour of men and women. Some people assert that the differences between male and female behaviour are purely hormonal, others that they are strictly cultural – that is, the result of upbringing.
The truth probably lies somewhere in the middle. What is certain is that the sex hormones are responsible for the differences in the appearances of men and women, in the form of a large difference in the amount of muscle and a totally different distribution of body fat.