These age preferences were confirmed in marriage records with males marrying females younger than them and vice versa.
This study used 21,245 participants between 18 and 65 years of age who were not involved in a close relationship.
A British psychological study published in Evolution and Human Behavior in 2010 concluded that men and women, in general, continued to follow traditional gender roles when searching for mates.
However, human males tend to have more parental investment compared to mammal males (although females still tend to have more parental investment).
Thus, both sexes will have to compete and be selective in mate choices.
These differences may be sexual, financial or social in nature. Socially, a society with a difference in wealth distribution between older and younger people may affect the dynamics of the relationship.
Although the "cougar" theme, in which older women date much younger men, is often portrayed in the media as a widespread and established facet of modern Western culture, at least one academic study has found the concept to be a "myth".
Differences in age preferences for mates can stem from evolutionary mating strategies and age preferences in sexual partners may vary cross culturally.
There are also alternative social theories for age differences in relationships as well as suggested reasons for 'alternative' age-hypogamous relationships.
Male chimpanzees tend to prefer older females than younger and it is suggested that specific cues of female mate value are very different to humans.
Buss attributed the young age preference for females to the cues that youth has.
A study released in 2003 by the United Kingdom's Office for National Statistics concluded that the proportion of women in England and Wales marrying younger men rose from 15% to 26% between 19.