A new study has found a link between men's and women's personalities and the likelihood of them having kids.
Men with neurotic personality traits are having fewer children compared to previous generations, according to the study.
The study examined the effect of personality on how likely a person is to have children, using extensive survey and birth registry data from Norway.
It also found that men who are extraverted and open tend to have more children, while women who rank as conscientious on personality tests tend to have fewer children, although these findings were constant across generations.
The study could have important implications for population dynamics at a time when fertility rates across developed countries have fallen to below replacement rates.
Personality effects may be one factor contributing to the decline of fertility rates in Europe, but they have not previously been studied in detail, IIASA's Vegard Skirbekk, who led the study, said.
Population changes are an important factor for projecting future changes in sustainability, climate, energy, and food security, IIASA's core research areas.
In particular, Skirbekk notes the decline in childbearing among neurotic men-neurotic meaning individuals who tend to be moody and emotional.
The study found that the effect only applies for men born after 1957.
Skirbekk said that the change in these men's fertility could be due to new norms in having children, for example that couples today wait longer to have children, and couples tend to test each other out more before committing to raising children together.
The study is published in the European Journal of Personality.