Development of the unborn child is possible because humans have very specialized reproductive systems.
Babies require many years of development before they themselves are able to reproduce.
Puberty Puberty refers to the changes that take place in boys and girls to bring about sexual maturity. A biological clock, located inside the brain, decides when the body is ready for these changes to begin and then stimulates the release of chemical signals, called sex hormones, to cause the developments that turn boys into men and girls into women. At this stage, boys and girls become more interested in each other. All of the developments that take place during puberty are known as secondary sexual characteristics. Hormones are powerful chemicals that control or influence particular functions of the body.