Nature vs Nurture: well-matched opponents

Researchers studying thousands of human traits have concluded that, overall, they are influenced equally by genetic and environmental factors.

By comparing data from over 50 years' of twin studies, Dutch and Australian scientists say that 49 percent of almost 18,000 traits studied are mostly influenced by genetics and 51 percent are mostly influenced by environmental factors.

However, the relative influence of the two factors varied significantly between types of traits. For example, the risk of bipolar disorder was almost 70 percent influenced by genetics while the risk of eating disorders was only 40 percent due to genetics.

The researchers noted that the heritability of traits was not random, but fell into clusters. So, while neurological, ophthalmological and skeletal traits tended to be highly heritable, traits related to values and attitudes had some of the lowest heritability values, implying that environmental factors play a greater role in such traits.

Suggesting that it is time to move away from the traditional 'nature vs nurture debate', lead co-author Dr Beben Benyamin from the University of Queensland, Australia comments that we should 'instead look at it as nature and nurture'.

Overall, he and his colleagues found that all of the studied traits have some sort of genetic influence, with around two-thirds attributable solely to the cumulative effects of genes.

Dr Benyamin told the Guardian: 'Genetics contribute to all traits - the difference is, by how much.'

The research, reported in Nature Genetics, reviewed studies carried out between 1958 and 2012, including more than 14 million twins worldwide.

These used a classic twin-study design to compare non-identical to identical twins. These are conducted on the rationale that, while it can be assumed that environmental factors have been the same for each pair of twins, the genetic make-up is different for the non-identical twins. Such studies can therefore identify the influence of genetic heritability.

However, the authors note that data from twin studies alone are insufficient to explain why certain traits might deviate from a simple genetic pattern of inheritance.

'Additional data are required, for example from large population samples with extensive phenotypic and DNA sequence information, detailed measures of environmental exposures and larger pedigrees, including non-twin relationships,' they comment.