Mum Dad Gave Me Half My Happiness

An exceedingly silly and misleading headline from the Health and Science section of Times of India:

Half of our happiness lies in genes

A study showed that personality traits including those such as propensity to worry, sociability and some others which predispose a person to happiness are hereditary. The study was done using 900 twin pairs. The conclusion:

The researchers say that although happiness has its roots in our genes, around 50% of the differences between people in their life happiness is still down to external factors such as relationships, health and career.

The interpretation by media:

Therefore 50% of our happiness is in the genes. Notice I highlighted "our". Because herein lies the misunderstanding of the quantity 50%. The common sense notion of heredity is that parents pass on traits to their children. The common interpretation of this is that since personality traits may be inherited, this study shows that an individual inherits 50% of the capacity to be happy from his/her parents. This is simple untrue and a completely meaningless statement. What was been measured in the study using twin pairs is heritability, which is the proportion of variation of the trait in the sample population that is attributable to genetic differences between individuals. Heritability is a population concept. It says nothing about the role heredity plays in the development of the trait in an individual. So, a heritability measure of 0.5 does not mean that 50% of the trait in an individual is because of genes. In a study if we measure heritability of height to be 80% then it does not mean that about 4 feet 9 inches of the height of a 6 feet tall person is due to genes and the rest due to the environment. It simply means that 80% of the variation in height in the population may be attributable to genetic differences between individuals. This number can change with the sample studied. If you sample a population subjected to a wide variation in environmental conditions such as accessibility to good nutrition, sanitation etc, then the heritability measure of height will be much less, since more of the variation in height is explainable by the differences in environmental conditions faced by different individuals. In contrast if we measure heritability in a population that faces a more homogeneous environment, then any differences in height between individuals are more likely to be due to genetic differences and that sample will have a high heritability value for height. Heritability estimates by themselves do not say anything about the particular genes that contribute to that trait. Genes are not blueprints for traits. Genes and environment interact in complex ways during development to build the phenotype.

Yet the media never learns. The Times report was a copy and paste of a press release. Despite stating in the report that 50% of the differences between people.... there was no mention that what was actually measured in the study was heritability, let alone an attempt to explain the difference between heredity and heritability. I caught the last bit of a CNN report on TV and they too had a headline to the effect that 50% of human happiness is genetic, reinforcing the misconception that an individual inherits 50% of the capacity to be happy from parents.

I'm glad that the Times has a health and science section. But I am less that half happy at the awful reporting :-)