Sibling Psychology: Lastborns Aren’t Daredevils After All

Study refutes the idea that birth order influences people’s risk propensity

Some ideas and assumptions are so common that they are generally accepted as true. For example, the idea that lastborn children are more willing to take risks than their older siblings. Using three large data analyses, a team of researchers from the Max Planck Institute for Human Development, the University of the Balearic Islands, the University of Basel, and the German Institute for Economic Research have now shown that there is no relationship between birth order and individual risk-taking propensity. Their results have been published in PNAS.

Charles Darwin, Alexander von Humboldt, and Rosa Luxemburg were the youngest children in their families and had character traits that are often attributed to lastborns: They were intrepid, adventurous, and rebellious. The idea that birth order influences personality has been a topic of heated discussion in psychology and beyond for some time. It came to the fore in the 1990s, with the work of science historian and Darwin expert Frank Sulloway. In trying to pinpoint why people become political or scientific revolutionaries, Sulloway found that lastborns are statistically more likely to take these routes. According to his family dynamics model, firstborns can be sure of their parents' undivided attention, whereas younger siblings have to fight for a "family niche." That leads them to take risks that in turn shape their personality.

Sulloway's family dynamics model is now viewed more critically, and recent studies have found no relationship between birth order and personality in general. But does the same apply to the willingness to take risks? Are lastborns more reckless than their older siblings? A team of researchers from the Max Planck Institute for Human Development, the University of the Balearic Islands, the German Institute for Economic Research, and the University of Basel conducted three analyses to investigate these questions.

First, the researchers examined data from one of the most comprehensive scientific surveys in Germany, the Socio-Economic Panel (SOEP). Each year, the SOEP surveys around 30,000 people on a variety of topics, including their self-assessed willingness to take risks in contexts such as driving and financial decisions. The researchers compared the responses of firstborns with those of their younger siblings. In 96% of the comparisons, no relationship was found between birth order and risk-taking propensity.

Second, the researchers re-analyzed data from the Basel–Berlin Risk Study. This study examined the individual risk propensity of 1,507 adults in experimental behavioral tests in the laboratory as well as in self-report measures. Again, they found no correlation between birth order and willingness to take risks.

Third, the researchers looked at the birth order of almost 200 famous explorers and revolutionaries. “We wanted to rule out the possibility that lastborns might be more willing to take risks in real life, but that this trait doesn’t show up in surveys or behavioral tests. So we consulted the history books to see whether the risky life choice of becoming an explorer or revolutionary depends on birth order. But we found no statistical patterns there either,” says Tomás Lejarraga, lead author of the study, Adjunct Researcher in the Center for Adaptive Rationality at the Max Planck Institute for Human Development, and Associate Professor at the University of the Balearic Islands in Mallorca.

“The idea that family dynamics—which could be impacted by birth order—influence the willingness to take risks seems intuitive and plausible. But we found no evidence for it in survey data, experimental data, or examples of famous risk takers from history,” says Ralph Hertwig, Director of the Center for Adaptive Rationality at the Max Planck Institute for Human Development and co-author of the study.

Given that Martin Luther, Christopher Columbus, and the British explorer Mary Kingsley were also firstborns, there must be factors other than birth order that prompt people to choose a risky life.

Original Publication
Lejarraga, T., Frey, R., Schnitzlein, D. D., & Hertwig, R. (2019). No effect of birth order on adult risk taking. PNAS. doi:10.1073/pnas.1814153116