In male infants, between the thirtieth and sixtieth days after birth, there is a rise to about 260mg/100ml, which has so far been unexplained. It then gradually drops to the low childhood level. Particularly puzzling is the fact that it does not appear to be active, being 'bound' to SHBG (sex hormone binding globulin) which rises in both sexes. There is no rise in testosterone for female infants, and Bancroft(1) speculates that it may have something to do with the development of the male central nervous system.
At five, children traditionally began formal learning in earnest, whether as a member of a tribe or in a Western school. Boys used to change to long trousers at eight. Whether such changes are simply a traditional pattern of social organisation, or a sense of biological changes, rites of passage indicate tacit agreement that there is a pattern.
Piaget developed an elegant description of childhood cognitive development, while Kohlberg extended this into perceptions of gender. Yet we are only just beginning to investigate the cognitive implications of sexual development in childhood.
Where there is no parental care in species complex behaviours have to be genetically programmed to ensure that mating occurs. Where there is care of the young, they have been shown to demonstrate sexual imprinting, sometime after birth, or hatching, when they are nearing maturity. Thus male ducklings are said to imprint on their mother, and so will mate with female members of their own species. Where only one parent cares for the young, sexual imprinting is said to be confined to one sex. In some species, the imprinting is more specific, occurring with individuals similar to their family, but not exactly the same. Thus they are more likely to mate with distant, rather than close, relatives. Even in animals, there much still to be researched. How, for instance, does imprinting work when both parents provide care for the young?
However, among humans and the primates, with complex socialisation patterns, it is may be that if there are genetic substrates for behaviour patterns, sexual or otherwise, they are likely to be more generalised. The problem is that what is learned depends on how it is learned. Human beings exhibit a bewildering array of sexual 'turn ons,' from power and money, through to immense collections of shoes.
At about the age of six the adrenal glands begin to produce androgens in both sexes. These are thought to promote the start of further sexual development and stimulate the early growth of pubic hair.
Having reluctantly admitted the fact of infant sexuality, following Freud's idea of a latency period, developmental studies also tended to assume that not much happened until teenage. In fact, a great deal goes on. There seems to a tacit assumption that sexual imprinting occurs in humans, but little research.
Whether there is anything as complex as Money's Lovemap Template,(2) which proposes an innate substrate, comparable to Chomsky's Language Acquisition Device, combining with experiential factors, is debatable. It may be intuitively assumed, however, that, there is a period in late childhood, when there is a particular sensitivity to cues which form the erotic focus. Given that any hypothesis would be difficult to test, the question about what proportion is innate and what is learned is a subject of massive scientific indifference, or perhaps, negativity.
Yet, as Reiss(3) says: "Do we really want our scientists to be neutral and silent on issues that tragically impinge on our lives? . . . ."
Around ten, control by the hypothalamus changes. This allows a rise to occur in various steroids, which are produced partly, but not exclusively, by the gonads. This is clear because the rise in occurs even in children without gonads. The earliest signs are nocturnal surges in the levels of gonadotrophins.
Androgens promote increased muscle bulk, in combination with exercise, a fact well known to body-builders. Bone growth in terms of body size seems to be influenced by the SRY gene, as we said in the last chapter. The exact contribution of each to male maturation is unclear, though it may be significant that the adolescent growth spurt in boys is probably dependent on an initial low concentration of testosterone. This occurs between 11 and 16, and lasts for about eighteen months, Testosterone begins to rise steeply until the age of 15 to 17, bringing the growth spurt to an end, and from 17 to the early twenties, rises more slowly to the adult levels.
In girls, the growth spurt starts two years earlier, with the first period occurring at about 13 years.
The first ejaculation in boys is about 11, though full virility is presumably not attained until later. For both boys and girls, there is a variation of two or three years either way, a feature in development that may well be an unwelcome addition to the teenage child's problems.
It is thought that testosterone also increases storage of calcium, phosphorus, and promotes the production of more red blood cells. In girls, estrogen and progesterone redistribute fat around the body - the so-called 'pears rather than apples'
Bland, J., (1998) About Gender: Physical Development.
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Last amended 12.05.98