Breaking rules and taking risks with casual sex and binge drinking are inevitable for teenagers, according to a new study. Parents should thus stop condemning their offspring's difficult behaviour and accept it as a necessary part of human development, researchers add. "Heightened risk-taking during adolescence is likely to be normal, biologically-driven, and, to some extent, inevitable. There is probably very little we can or ought to do," the Daily Mail quoted Laurence Steinberg, of Temple University in Philadelphia, as saying. "This is a development shift that likely has evolutionary origins," he added. In the study, Steinberg found that though more than 90 per cent of all high school students (in the U.S.) have had sex, drug and driver education in their schools, large proportions of them still have unsafe sex, binge drink, smoke and drive recklessly. Another study he did with psychologist Jason Chein, which measured brain activity in adolescents and adults, showed teenagers are more likely to take risks in groups. As part of an experimental game, adolescents playing alone behaved in a similar way to adults, but the teenagers took more risks when they knew friends were watching. Professor Steinberg said teenagers find socialising with their peers rewarding, so it makes their brains more susceptible to receiving rewards.