Hugh Hefner or Michael Douglas are just faithful followers of an evolutionary pathway. A new statistical research published in "Biology Letters" reveals that monogamous men indeed have more children if their wives are younger than them, more exactly, by 4 to 6 years.

The research team used the data from a Swedish research, applied a simple equation to the age difference of the parents and the number of offspring, and discovered that, in the case of the adults keeping monogamous relationships throughout adulthood, the highest number of children was delivered by couples in which the husband was 4 to 5.9 years older than the wife.

"Men want women younger than themselves because they are physically attractive, while women tend to prioritize a partner who can provide security and stability, and so tend to opt for older men," said co-author Martin Fieder at the University of Vienna.

Others stress that it is not about the age difference, but the age of the mother.

"The age of the mother is likely to be more important than any age difference: the older the mother, the lower her chances of having more children," said Erik Lindqvist at the Research Institute of Industrial Economics in Stockholm, Sweden.
But the measurements have showed that this factor does not count much.

"We added that factor into the calculation. The importance of the age difference didn't change," said co-author Fred Bookstein, statistician at the University of Washington.

Still, this pattern does not fit in any culture. A Finnish research published last year in "Biology Letters" investigated the case of the Saami (Laps) people of preindustrial Finland, finding that men had to marry a woman about 15 years younger.

The team gathered data from church records of 700 couples from the Utsjoki, Inari and Enontekiö settlements going from 17th to 19th century, with the purpose of taking out of the equation the child survival boosted by modern medicine. The women's age was the main factor influencing the biological success (translated in the number of surviving children): the younger the woman, the more healthy children she could deliver. An old wife or husband decreased significantly the couple's fertility.

Anyhow, I cannot imagine anyone today in the western world regarding himself/herself biologically unsuccessful with no more than 1-2 kids. On the contrary...