Dads have always tended to be older than mums

Men have consistently had children later in life than women according to a study mapping conception age over the past 250,000 years of human history.

Researchers found that the average age of conception over that period was 26.9 years old, but with over seven years difference in average age for men and women: women conceived on average at age 23.2, while their male partners had an average age of 30.7. They also noted the remarkable consistency of these parental ages over much of human history, with an increase in female generation time only evident more recently.

'Through our research on modern humans, we noticed that we could predict the age at which people had children from the types of DNA mutations they left to their children', said Professor Matthew Hahn, co-author of the study published in Science. 'We than applied this to our human ancestors to determine what age our ancestors procreated'.

The team from Indiana University, Bloomington looked at the number of de novo genetic mutations occurring in offspring over three generations of 1500 Icelanders and used these to create a model that associated these mutations with the age their parents were when they conceived them. They used this model on a sample of 2500 modern people living across the globe to discern the timespan of generations throughout history.

This information can tell us a lot about the historical social organisation of humans, as well as the environmental challenges presented to our ancestors, the authors argued. Lead author Dr Richard Wang told Nature he thought longer generation times for men existed as men are biologically able to have children later in life than women, bringing up the average age of fatherhood.

But other societal influences might also be at play, such as a patriarchal society putting pressure on men to gain status before fatherhood, said Professor Mikkel Schierup, a population geneticist at Aarhus University who was not involved in the study, or the more recent increase in female education and women pursuing careers delaying the age of motherhood.

Notably, the model used in this study is based on the signature of mutations resulting from parental age, and some critics of the work note that other factors – such as environmental exposure – can cause mutations which might be misattributed to parental age. In the future, a more confident assessment of parental ages through history will likely require sampling more populations, suggested Professor Schierup.

For now, this study provides 'sensible estimates' which can be used along with archaeological and anthropological findings to piece together human history.