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).
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.
Another study also showed a higher divorce rate as the age difference rose for when either the woman was older or the man was older.
But the rule of seven may not actually describe what people consider acceptable.
In 2001, a team of Dutch social psychologists, led by Bram P.
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.
The study found that, as supported by other academic studies, most men preferred younger, physically attractive women, while most women, of any age, preferred successful, established men their age or older.
Age disparity in sexual relationships is the difference in ages of individuals in sexual relationships.
Concepts of these relationships, including what defines an age disparity, have developed over time and vary among societies.
Muhammad might not have been the most reliable relationship counselor, though; he was also concerned about height disparity: “a tall man married to a too short woman, or vice versa … Now, the half-your-age plus seven rule has entered the cultural lexicon.
It’s defined ten times on Urban Dictionary, gets its own section in Wikipedia’s page on age disparity in sexual relationships, is espoused by Barney Stinson on “How I Met Your Mother” and is referenced by and The Awl.