Bucknell Study Links Personality Traits to Family Size Across Cultures

When it comes to family size, personality may matter more than you might think.

Bucknell University Professor T. Joel Wade, psychology, is a co-author of a new international study that found people who are more outgoing and agreeable — and less prone to negative emotions — tend to report having more biological children.

The study, published earlier this month in the professional journal Culture and Evolution, examined the relationship between the Big Five personality dimensions — openness to experience, conscientiousness, extraversion, agreeableness and neuroticism — and the number of biological children participants reported having. Researchers analyzed representative samples from more than 15,000 participants in the United States, Canada and Japan.

Higher levels of extraversion and agreeableness were significantly associated with having more children, while higher levels of neuroticism were associated with fewer. Contrary to researchers’ expectations, openness and conscientiousness showed no significant relationship with the number of children.

"This study confirmed that personality can have a role in these reproductive decisions," Wade says. "There have been studies looking at individual Westernized countries and a few looking at non-Westernized countries, but no one had done this comparison of Westernized and non-Westernized countries together."

Pairing with Similar Personalities
Wade, whose research focuses on evolutionary social psychology and human relationships, says the results make sense in light of previous research showing that people often pair with partners who share similar personality characteristics.

"If you've got a couple of extroverts together or a couple of agreeable people together, there isn't going to be as much conflict about what to do," he says. "You're positive, your partner is positive, you're highly sociable — all those characteristics can help with that."

The researchers suggest extraversion may support reproductive outcomes by expanding social networks and opportunities to find partners, while agreeableness may contribute to the relationship stability needed for cooperative parenting. Lower neuroticism, meanwhile, may reduce chronic stress and relationship difficulties that can affect reproductive and relationship outcomes.

The study also found significant associations involving demographic factors. Married participants, women, older participants and heterosexual participants reported more biological children. Participants in the United States and Canada also reported more children than those in Japan.

Findings Across Cultural Differences
For Wade, one of the study's most notable findings was the similarity of the broad personality patterns across three culturally distinct countries.

"The greatest surprise was that there was pretty much consistency across the three countries," he says. "Japan is a little different, but the fact that the personality dimensions linked to having more children show up basically in all three countries was both welcoming and surprising."

The researchers say the findings demonstrate that personality is only one part of a much more complicated picture. Cultural expectations, economic conditions, relationship status and other demographic factors can influence whether and when people have children, potentially strengthening or weakening the effects of individual personality traits.

That may help explain why conscientiousness, despite its links to relationship satisfaction in previous research, was not associated with family size.

The cross-cultural dimension was especially important because Canada and the United States share relatively individualistic cultures, while Japan has traditionally placed greater emphasis on collectivism.

"It was really nice to have Canada and the United States, where there are some slight differences, and then Japan, which is a very different society," Wade says. "Having such large samples and the multicultural aspect is really valuable."

The researchers plan to continue exploring how personality interacts with cultural, social and economic conditions to influence reproductive decisions, particularly as many developed nations confront declining birth rates and aging populations.