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.An overarching evolutionary theory which can provide an explanation for the above mechanisms and strategies adopted by individuals which leads to age disparity in relationships is called Life History theory, Life History theory posits that individuals have to divide energy and resources between activities (as energy and resources devoted to one task cannot be used for another task) and this is shaped by natural selection.Parental Investment Theory refers to the value that is placed on a potential mate based on reproductive potential and reproductive investment.
A 2003 AARP study reported that 34% of women over 39 years old were dating younger men.
In females, relative youth and physical attractiveness (which males valued more compared to females) demonstrated cues for fertility and high reproductive capacity.
Buss stated the specific age preference of around 25 years implied that fertility was a stronger ultimate cause of mate preference than reproductive value as data suggested that fertility peaks in females around mid-twenties.
Females demonstrate a complementary pattern, being willing to accept considerably older males (on average 8 years older) and were also willing to accept males slightly younger than themselves (on average 5 years younger).
This is somewhat different to our close evolutionary relatives: chimpanzees.