Some of us know exactly what we want to do with our lives while others are less sure; some thrive in exam conditions while others underperform; and some are broadly satisfied with life while others are unhappy with the way things work out. As human beings we differ in many ways from each other, and decades of genetic research have shown that these differences have their origins in both DNA and life stories. We recently completed a study that dug into some TEDS twins’ life stories in order to better understand the experiences that explain some of the differences we observe in human behaviour.

For most behaviour the experiences that matter have been found to be specific to individuals. These are experiences that either only affect one member of a family (e.g. a best friend or a broken leg), or which affect one sibling differently to another (e.g. problems at home). They are known in the research literature as non-shared environmental (NSE) experiences. We have known that these NSE effects matter for around three decades but have struggled to identify the specific experiences that make a difference.

In an effort to generate new ideas about these NSE experiences we asked almost 500 monozygotic (MZ) twin pairs to tell us about the differences between them, and about aspects of their lives that they (and their parents) saw as explaining those differences. Only NSE effects can explain differences between MZ twins because they share their genes and much of their environment, both of which make them similar to each other rather than different.

Twins and their parents told us that the experiences they believed to have led to differences between them in GCSE performance included their perceptions of teachers (e.g. were they good teachers and did they have a good relationship with them?) and of themselves (e.g. self-belief). In describing differences in mental health and self-confidence many told us that different experiences of friendship had been important. We tested ideas related to GCSE performance with a sample of 2165 twin pairs and have plans to test the ideas related to peer relationships in future work. If you would like to read more about this study's findings please click here for the public report.

Linked documents describing the study:

• Public report
• Executive summary
• Paper published on line by AERA, Nonshared Environmental Influences on Academic Achievement at Age 16. A Qualitative Hypothesis-Generating Monozygotic-Twin Differences Study.