Researchers have found that childless people tend to have more permissive social attitudes and that having children, rather than aging, helps explain why other people tend to become less permissive.

“There is this idea that as you get older you become more conservative from experience and from being bitten by the real world,” said Dr Nick Kerry, co-author of the research from the University of Pennsylvania.

“But it doesn’t seem to be the case. If you look at people who are not parents, you just do not see an age difference.” What changes people’s attitudes instead appears to be having children.

The study potentially offers a fresh take on the decline in birthrates seen in many countries. “I think it could contribute to liberalisation in those countries,” said Kerry. Many countries now have fertility rate well below replacement level.