Genes or the Enviroment (Age-old nature nurture debate almost finalizes)

How much our genes or environment takes part in our development has been calculated by a meta analysis of 5 decades of twin studies. 
 
In a study published recently, an international team of researchers shows an almost 50-50 split in the influence of genes or the environment on the development of various human traits.
The finding, published in Nature Genetics, is based on a review of 2748 studies involving 14 million twin pairs from across 39 countries.
The twins involved in the various studies ranged in age from 18 to 64 years.

Co-first author Dr Beben Benyamin (in photo above) says:
"there was some controversy and differences in terms of how much of the variation [in traits] is due to genetics and how much is due to environment,"

He says the team, including Dutch and American researchers, looked at all published twin studies to answer this puzzle.
Benyamin says while identical twins are genetically the same, non-identical twins share 50 per cent of their DNA.
The researchers were able to determine the contribution of genetics and the environment on the trait by measuring how similar various traits are between identical twins and non-identical twins.

"If the trait is genetic then you would expect identical twins will be more similar than the non-identical twin. The more similar an identical twin to a non-identical twin then we can infer the trait is largely due to the genetic factor,"  says Benyamin.

For all traits, the average genetic influence was 49 per cent while the environment accounted for 51 per cent.

"We were amazed the number was so close to half," admits Benyamin.

However, he says, this is an average figure and some traits are more or less influenced by genes.
For example:
*schizophrenia is 70 per cent the result of genetic influences and 30 per cent environmental.
 *social values are shaped by around 30 per cent genetics, and 70 per cent socio-economic factors.


The researchers also found almost 70 per cent of the effect of genes on a trait is additive.
This means that where hundreds of genes are involved in a trait, such as height, each gene has a tiny cumulative impact.

"So for example in height one gene might add one centimetre, the next gene a half a centimetre," Benyamin says.

This finding has implications on the design of gene mapping studies, says Benyamin, as it enables researchers to adopt the correct modelling.

"We comprehensively reviewed everything in the literature of twin studies — and we found everything is inherited, but the degree to how much the genetics contributed varies between traits and phenotype."

Since the birth of psychology, the psychologists have been fighting over the share of nature or nurture in the development, as illustrated below showing different psychological models and their viewpoint.




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