Age-disparity relationships have been documented for most of recorded history and have been regarded with a wide range of attitudes dependant on sociocultural norms and legal systems. Relationships with age disparity of all kinds have been observed with both men and women as the older or younger partner.In various cultures, older men and younger women often seek one another for sexual or marital relationships.Differences in age preferences for mates can stem from evolutionary mating strategies and age preferences in sexual partners may vary cross culturally.
Parental Investment Theory refers to the value that is placed on a potential mate based on reproductive potential and reproductive investment.
As well as asking participants a number of questions on mate selection criteria, they also had to provide the oldest and youngest partner they would accept.
It was found that for all ages males were willing to accept females that are slightly older than they are (on average 4.5 years older), but they accept females considerably younger than their own age (on average 10 years younger).
The study found very few instances of older women pursuing much younger men and vice versa.
Within sexual selection Darwin identified a further two mechanisms which are important factors in the evolution of sex differences (sexual dimorphism): intrasexual selection (involve competition with those of the same sex over access to mates) and intersexual choice (discriminative choice of mating partners).