Identical twins are not so identical, study suggests

Research finds they differ by an average of 5.2 early mutations, adding new perspective to nature-versus-nurture debates

Genetic differences between identical twins can begin very early in embryonic development, according to a study that researchers say has implications for examining the effects of nature versus nurture.

Identical - or monozygotic - twins come from a single fertilised egg that splits in two. They are important research subjects because they are thought to have minimal genetic differences. This means that when physical or behavioural differences emerge, environmental factors are presumed to be the likely cause.