Twin research: duplicate or one-off?

Is it our genetic make-up, lifestyle choices or the environment that determine who we are, what we look like or how long we live? Five findings from twin research.

Text: Julie Freudiger; photo: José León/Unsplash

For decades, twins have been the ideal test subjects for researchers interested in examining the impact of nature vs. nurture. Although monozygotic twins have an identical genetic make-up because they are formed from the exact same sperm  and egg of their father and mother, they are not simply copies of each other. Researchers are very interested to know why this is the case. Twin studies also compare monozygotic and dizygotic twins. The latter share only half their genes, but tend to grow up under the same conditions. Comparisons like these help researchers find out which traits are hereditary. The insights gained from twin studies can also be applied to people who aren’t born as a pair.

1. Intelligence is inherited,  but nothing grows without water

Anita Rauch, professor of medical genetics at the University Hospital of Zurich, says “intelligence and talent are about 80% inherited”. But external factors determine whether the genetic potential is leveraged or not. 

2. To some extent, our health is in our hands.

Many illnesses, such as migraines, high blood pressure, diabetes, acne and rheumatism, are inherited, “but external factors such as exercise or stress also play a role”, says Rauch. Current studies with identical twins show that environmental factors even influence the course of diseases such as breast cancer or multiple sclerosis. 

3. Living to old age is not inherited

A twin study conducted in the UK indicates that your genes don’t play a big role in how long you live. The twins observed in the study died at very different ages and from different diseases. “Moreover, the cluster of cells from which identical twins are formed does not always divide into two equal halves”, Rauch explains. This means that only one may suffer from an inherited illness. 

4. The environment alters genes 

Studies with identical twins have shown that environmental factors can activate or deactivate genes, because the longer that twins live apart from each other , the greater the differences in their genes. So, your genetic make-up is not set in stone. In the same way,  genes also have an impact on your environment. For example, if you like to take risks, you look for friends with a similar outlook. And this  reinforces the starting point of the genes. 

5. There is no personality gene

Genes do determine our basic characteristics. However, identical twins have the same genetically identical blueprints and live in the same environment, but they still have two different personalities. On the one hand, studies show that all people experience the same environment differently and are thus shaped by it in different ways – even identical twins. On the other hand, twin studies show that  personality traits, such as risk-taking or sociability, are inherited – between 30% and 50% depending on the study. However, researchers are yet to find a “personality gene” .