These relationships become significant because they begin to help the adolescent understand the concept of personalities, how they form and why a person has that specific type of personality. Some of the issues first addressed by this group include: Adolescence is a sensitive period in the development process, and exposure to the wrong things at that time can have a major effect on future decisions. Adolescence is marked in red at top right. Research also indicates that baseline sensation seeking may affect risk-taking behavior throughout the lifespan. For example, without a willingness to take risks, teenagers would not have the motivation or confidence necessary to leave their family of origin. Colour pin-ups of pop and film stars of the day were at the heart of the title, along with 'dreamy picture love stories', which evolved into photo strips, fashion and beaty shoots and the cathy and Claire problem page. The first facial hair to appear tends to grow at the corners of the upper lip, typically between 14 and 17 years of age. This may help explain sex differences in athletic performance. Three neurotransmitters that play important roles in adolescent brain development are glutamate , dopamine and serotonin. Some have argued that there may be evolutionary benefits to an increased propensity for risk-taking in adolescence. Girls attain reproductive maturity about four years after the first physical changes of puberty appear. The testes primarily release testosterone , and the ovaries predominantly dispense estrogen.