A lengthy study that involved 50 years of observation has yielded definitive results about nature vs. nurture, settling a several century-long debate that started as early as 1690 when philosopher John Locke coined the term tabula rasa ("blank slate") in the work "An Essay Concerning Human Understanding."

The report titled "Meta-analysis of the heritability of human traits based on fifty years of twin studies" was published in Nature Genetics, and the long-running research examined twins for half a century before discovering that 51 percent of human traits and disease variations can be attributed to environmental factors and 41 percent of variation can be accredited to genetics. Also, the publication unveiled the results of the cumulative effect of genetic differences.

"When visiting the nature versus nurture debate, there is overwhelming evidence that both genetic and environmental factors can influence traits and diseases," the study's lead researcher Dr. Beben Benyamin said in a statement. "The findings show that we need to look at ourselves outside of a view of nature versus nurture, and instead look at it as nature and nurture."

Dr. Benyamin, who's from the Queensland Brain Institute, worked with researchers at VU University of Amsterdam. Together they studied 2,748 classical twin studies, and involved more than 14.5 million pairs of twins between 1958 and 2012. Identical twins were compared against non-identical twins during the twin studies due to the fact that identical twins possess identical genetic makeup while non-identical twins share just half of their genes. Researchers examined precisely 17,804 trait variations, including tobacco use and depression, to determine whether traits linked with non-identical twins were additionally influenced by environment.

Environment and genetics contribute equally to traits. However, they did find variations in individual traits. For instance, 70 percent of bipolar disorder is due to genetics and other 30 percent can be ascribed to environmental factors. Also, the risk of developing eating disorders was found to be 60 percent environmental and 40 percent genetic.

The report carries vital implication for treating diseases simply by identifying the genetic and environmental influences that impact disorders. The research was also able to pinpoint genetics' increased impact on mental disorders and skeletal traits, while environmental factors play a more significant role in social values.

Nonetheless, genetic and environmental influences were balanced across most traits. The complex traits in humans have two parents, which are environment and genetics. The study provides the most comprehensive analysis of trait variation to date, and it will likely guide future gene-mapping efforts.

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