Within the non-pathological realm, there are many factors that influence the timing of puberty in addition to the fact that girls enter puberty on average 2 years before boys. There is a familial tendency in the timing of puberty, and those in more affluent and privileged societies enter puberty earlier. Well nourished children tend to go into puberty earlier than those who are thinner and this is particularly evident with girls. When underweight is severe, delay is almost inevitable as in anorexia nervosa. Those who undertake extreme competitive training for sports commonly are late in going into puberty , perhaps linked with a reduction in fatness rather than being underweight. Prolonged physical or psycho-emotional stress as in neglect or abuse has a powerful adverse effect on the timing of puberty not necessarily due to undernutrition.