So far it's a draw.
For instance, a massive meta-study, reported in Nature Genetics, quantified the heritability of human traits by analyzing more than 50 years of data on almost 18 thousand traits measured in over 14.5 million pairs of twins. They determined that heritability accounted for 49 percent of all traits and environmental influences for 51 percent.
They essentially found that genes and the environment play an equal role in human development. But that isn’t the end of the debate.
Researchers at Osaka University Graduate School of Medicine in Japan have now added a twist. They used positron emission tomography (PET) to examine how genetics and environmental factors affect the brain, as reported in the March issue of Journal of Nuclear Medicine.
The researchers used PET imaging to measure the glucose — or energy — metabolism throughout the brain. The authors explained their motivation in the JNM article:
The patterns of glucose metabolism in the brain appear to be influenced by various factors, including genetic and environmental factors. However, the magnitude and proportion of these influences remain unknown.
The researchers studied 40 identical twin pairs and 18 fraternal twin pairs. Any differences between identical twins is expected to be due to environmental factors since they are genetically identical, whereas fraternal twins only share half of their genes on average.
The researchers compared imaging results between the two types of twins to estimate the extent of genetic and environmental influences. When a genetic influence is dominant, the identical twins would have more trait similarity than fraternal twins. When an environmental influence is dominant, the trait similarity would be the same for identical and fraternal twins.
The researchers found that both genetic and environmental factors influenced glucose metabolism in the brain, but they predominantly affected different areas. Genetic influences played a major role in the left and right parietal lobes and the left temporal lobe, whereas environmental influences were dominant in other regions of the brain.
The brain's parietal lobes process sensory information such as taste, temperature and touch, and the temporal lobes process sounds and speech comprehension. More research is needed to understand why these areas of the brain were shaped more than other regions by genetics.
In addition to adding new information to the "nature verses nurture" debate, these results could be applied to other research areas, such as using imaging to better understand the underlying cause of Alzheimer’s disease or psychiatric disorders. Identifying which regions of the brain are more influenced by genetics or the environmental may add critical information to help better understand and treat diseases.
Previously: In human defenses against disease, environment beats heredity, study of twins shows, Wishing for a genetic zodiac sign: how much can genes really tell us about personality? and Nature/nurture study of type 2 diabetes risk unearths carrots as potential risk reducers
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