The age-old question of whether human traits are determined by nature or nurture has been answered, a team of researchers say. Their conclusion? It ’ s a draw. By collating almost every twin study across the world from the past 50 years, researchers determined that the average variation for human traits and disease is 49 percent due to genetic factors and 51 percent due to environmental factors.

University of Queensland researcher Beben Benyamin from the Queensland Brain Institute collaborated with researchers at VU University of Amsterdam to collate 2, 748 studies involving more than 14.5 million pairs of twins. “ Twin studies have been conducted for more than 50 years but there is still some debate in terms of how much the variation is due to genetic or environmental factors, ” Benyamin said.

He said the study showed the conversation should move away from nature versus nurture, instead looking at how the two work together. “ Both are important sources of variation between individuals, ” he said. While the studies averaged an almost even split between nature and nurture, there was wide variation within the 17, 800 separate traits and diseases examined by the studies. For example, the risk for bipolar disorder was found to be 68 percent due to genetics and only 32 percent due to environmental factors. Weight maintenance was 63 percent due to genetics and 37 percent due to environmental factors. In contrast, risk for eating disorders was found to be 40 percent genetic and 60 percent environmental, whereas the risk for mental and behavioral disorders due to use of alcohol was 41 percent genetic and 59 percent environmental.

Benyamin said in psychiatric, ophthalmological and skeletal traits, genetic factors were a larger influence than environmental factors. But for social values and attitudes it was the other way around.