It has long been a subject of debate: are human traits determined by nurture or nature? Now, a team of researchers has investigated whether our genes or the environment, where we have been raised in, influences who we are.
For the study published in the journal Nature Genetics on May 18, Danielle Posthuma, from the Vrije Universiteit Amsterdam, and colleagues looked at nearly every study on twins that has been conducted in the past 50 years.
They surveyed over 2,700 studies on twins to look at over 17,000 traits, comparing variations in identical twins, who share all their genes, and also the differences between fraternal twins, who share half their genes.
The researchers in particular looked at physical traits such as metabolism, height and weight as well as psychological traits, which include intelligence, personality, temperament and likelihood to suffer from depression.
They found that 49 percent of the average variation for human diseases and traits can be attributed to genetics. Fifty-one percent, on the other hand, can be attributed to environmental factors. They likewise found that about two-thirds of the traits are the result of the cumulative effect of many genes.
"Estimates of heritability cluster [register] strongly within functional domains, and across all traits the reported heritability is 49%," reported the researchers. "For a majority (69%) of traits, the observed twin correlations are consistent with a simple and parsimonious model where twin resemblance is solely due to additive genetic variation.
Although the results showed a near draw between nurture and nature, there were variations within the traits and diseases that were examined. Risks for bipolar disorder, for instance, were found to be 68 percent attributable to genetics. Thirty-two percent of the odds were due to environmental factors.
Odds for eating disorder were likewise 40 percent genetics and 60 percent environmental while risks for behavioral and mental disorders due to alcohol use were 59 percent environmental and 41 percent genetics.
Social values and attitudes were found to be largely influenced by environmental factors while ophthalmological, psychiatric, and skeletal traits are largely determined by genetic factors. The researchers, however, pointed out that there was no single trait without the contribution of genetic factors.
"What is comforting is that, on average, about 50 percent of individual differences are genetic and 50 percent are environmental," said Beben Benyamin, from the University of Queensland. "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."
Photo: Donnie Ray Jones | Flickr