Men with Younger women

According to Martin Fieder, an anthropologist at the University of Vienna in Austria, a woman should get together with a man several years older than herself if she wants a lot of children - at least in Sweden.

The analysis of Swedish birth records reveals that men who partner with women six years younger than themselves produce the most offspring.

Across many cultures men and women prefer younger and older mates respectively, says Martin Fieder. In theory these age preferences make evolutionary sense, he says. However, there has been little reliable data on whether the preferences translate into a real advantage in terms of having children.

To find out more, Fieder and Susanne Huber - his two-years-younger wife and a researcher at the University of Veterinary Medicine in Vienna - examined population data from Sweden. This country keeps meticulous records of births, including the names and ages of both parents, regardless of whether they are married or not.

They randomly selected the records of about 5600 men and 6000 women born between 1945 and 1955, and looked at the number of children born to each individual before 2003.

This is the most recent generation that could be assumed to have stopped having new children. Previous studies have shown that in Sweden only 2% of people have a child past the age of 45.

Six-year high

An analysis of the records revealed that men who had
younger women six years younger than themselves had the greatest number of children: about 2.2 children on average, a relatively high number in a country that has long had low fertility rates in the past.

By comparison, men who had partners six years older than themselves had 1.8 children on average.

Women bore the greatest number of children when they chose men four years older than themselves. Those who partnered with such men had 2.1 children on average.

The age-gap figures and numbers of children do not match up because the people studied were randomly selected from a large number of the Swedish population and therefore not likely to have been partners with each other, explain the researchers.
Evolved preferences

Fieder speculates that men evolved a preference for younger women because these women have a longer fertility span than older female counterparts. He adds that women, meanwhile, might give birth to more children when they choose older partners because such men are likely to have greater financial resources to support a family than younger men do.

However, men partnered with a much younger woman did not produce the maximum number of children. Mothers more than 10 years younger than their partners had about 2.0 children on average.

When too much of an age difference exists, there is perhaps a greater chance of male fertility problems and disagreement over family planning, suggests Fieder.

Fieder notes that his study relied on birth records and so did not include data on childless couples. He says that this could have skewed the results and hopes that future analyses will be able to include childless couples