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).
In August 2010, Michael Dunn of the University of Wales Institute, Cardiff completed and released the results of a study on age disparity in dating.
Dunn concluded that "Not once across all ages and countries ...
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 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.
This theory predicts both intrasexual selection and intersexual choice due to differences in parental investment; typically there is competition among members of the lower investing sex (generally males) over the parental investment of the higher investing sex (generally females) who will be more selective in their mate choice.
These two theories explain why natural and sexual selection acts slightly differently on the two sexes so that they display different preferences.
For example, different age preferences may be a result of sex differences in mate values assigned to the opposite sex at those ages.
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.