In evolutionary terms, the difference between 2.1 and 2.2 children is a lot more important than the small difference sounds, especially as it accumulates over time.

A new study in Royal Society Biology Letters says that achieving that maximum offspring count is best accomplished by men if their partner is approximately 6 years younger and by women if their partner is approximately 4 years older.

This means that a man may not just be interested in a trophy wife, he may be thinking about the future of humanity. But this happens with women also. Women who find a new mate still choose a partner older than themselves, though younger than the first.

Martin Fieder, in the Department of Anthropology at the University of Vienna, and Susanne Huber, from the University of Veterinary Medicine in Vienna ( editor's note: come again? ) did their study by examining 55 years worth of information from the Swedish national registries, detailing the number of births and age of parents.

A sample of 10,000 Swedish men and women who did not change their partners between the birth of their first and last child resulted in the age differences for maximum offspring they found.

They concluded that the age preference for the partner yields fitness benefits for both men and women and may thus be an evolutionarily acquired trait.

It's been a long-held belief that women prefer older men and men prefer younger women but this is the first study to demonstrate the optimum age differences if reproduction is important.

Article: Parental age difference and offspring count in humans