A culmination of more than half a century of research collected on 14.5 million pairs of twins has finally concluded that the nature versus nurture debate is a draw. According to the plethora of data, both have nearly identical influences on a person’s behavior, which suggests we need to stop looking at ourselves as a result of nature versus nurture, and instead realize we are a combination of both.

The recent study, published in the journal Nature Genetics, is the result of the collaboration between Dr. Beben Benyamin from the Queensland Brain Institute and researchers at the VU University of Amsterdam. They reviewed nearly every twin study ever done in the past 50 years. The impressive global twin review revealed that, on average, the variation for human traits and diseases is split almost equally.

“When visiting the nature versus nurture debate, there is overwhelming evidence that both genetic and environmental factors can influence traits and diseases,” Benyamin said in the press release. “What is comforting is that, on average, about 50 percent of individual differences are genetic and 50 percent are environmental.

The finding did not ring true for every case, however, as certain conditions leaned way more than others. For example, in the case of bipolar disorder, this was found to be around 70 percent genetic and only 30 percent due to environmental factors.

Although the finding may be unsatisfying for those hoping that one side of the spectrum held more weight than the other, according to Benyamin, the findings have “implications for choosing the best strategy to find genes affecting disease.” The data may also change the way that scientists approach the study of genetics. In about 69 percent of the cases, the twins' individual traits ended up being the cumulative effect of genetic differences.

“This means that there are good reasons to study the biology of human traits, and that the combined effect of many genes on a trait is simply the sum of the effect of each individual gene,” Benyamin explained.

Twin studies have been an integral part of science because of the unique genetic similarities between twin siblings. Identical twins develop from a single fertilized egg and they have the same genome. This means that any differences between the twins are due to their environment, not their genetics. For nearly a century scientists have used twin studies to better understand the extent to which certain traits are inherited.

Source: Polderman TJC, Benyamin B, de Leeuw CA, van Bochoven A, Visscher PM, Posthuma D. Meta-Analysis of the Heritability of Human Traits based on Fifty Years of Twin Studies. Nature Genetics. 2015.