From its time in the womb right through to old age, the male body is continuously adapting to the environment and to accommodate its own needs. And hormones play a crucial part in life's major changes.

Early days

Whether a baby develops into a boy or a girl depends on the pair of sex chromosomes they get from their parents. If there are two X chromosomes a girl develops, while a boy develops from a combination of an X and a Y chromosome.

Very early on in pregnancy, at about six to eight weeks, the Y chromosome kicks into action and triggers testes to develop - without a Y chromosome this embryonic tissue would have become ovaries. The foetal testis produces the male hormone testosterone and this promotes the development of the penis and scrotum. In doing this, testosterone prevents the formation of fallopian tubes, a womb (uterus) and vagina.

Puberty

In boys the process of sexual development, called puberty, starts between the ages of 12 and 15 and lasts for about four years. During this time hormones secreted by the pituitary gland in the brain, called follicle stimulating hormone (FSH) and luteinising hormone (LH), prompt the testes to produce more testosterone, causing a sharp increase in the levels of this male sex hormone.

This testoster