A theory that can explain this finding from an evolutionary perspective is the parasite-stress theory which explains that an increase of infectious disease can cause humans to evolve selectively according to these pressures.
Evidence also shows that as disease risk gets higher, it puts a level of stress on mating selection and increases the use of polygamy. In regions such as Sub-Saharan Africa the use of polygyny is commonly practiced as a consequence of high sex-ratios more males born per females and passing on heterozygous diverse genetics from different females to offspring. Another reason that polygynous communities have larger age-gaps between spouses is that intrasexual competition for females increases as fewer females remain on the marriage market with males having more than one wife each , therefore the competitive advantage values younger females due to their higher reproductive value.
Smaller than average age-gaps[ edit ] Comparatively in Western societies such as the US and Europe we see a trend of smaller age-gaps between spouses, reaching its peak average in Southern Europe of 3. Using the same pathogen-stress model we see a lower prevalence of disease in these economically developed areas, and therefore a reduced stress on reproduction for survival.
Additionally, it is common to see monogamous relationships widely in more modern societies as there are more women in the marriage market and polygamy is illegal throughout most of Europe and the United States. As access to education increases worldwide, the age of marriage increases with it, with more of the youth staying in education for longer. The mean age of marriage in Europe is well above 25, and averaging at 30 in Nordic countries, however this may also be due to the increase of cohabitation in European countries.
Social structural origin theory argues that the underlying cause of sex-differentiated behaviour is the concentration of men and women in differing roles in society. It has been argued that a reason gender roles are so prevalent in society is that the expectations of gender roles can become internalised in a person's self-concept and personality. Women and men tend to seek a partner that will fit in with their society's sexual division of labour.
For example, a marital system based on males being the provider and females the domestic worker, favours an age gap in the relationship.
An older male is more likely to have more resources to provide to the family. The picture often displays a stereotypical pairing of a divorced, middle-aged, white, affluent female dating a younger male with the relationship taking the form of a non-commitment arrangement between the partners. Sexual double standards in society, in particular, may account for their rarity. A number of variables have been argued to influence the likelihood of women entering into an age-hypogamous relationship, such as racial or ethnic background, level of education, income, marital status, conservatism, age, and number of sexual partners.
French President Emmanuel Macron and his wife Brigitte. The couple married in ; at the time he was 30 years old and she 54, demonstrating a year age gap between the pair.
Another example illustrating the varying literature surrounding age-hypogamous relationships is research indicating that a woman's marital status can influence her likelihood of engaging in age-hypogamous relationships. It has been found that married women are less likely to be partnered with a younger male compared to non-married women  in comparison to more recent findings, which provides evidence to suggest that previously married women are more likely to engage in an age-hypogamous sexual relationship compared to women who are married or who have never been married.
A recent study found that when shown pictures of women of ages ranging from 20—45 with different levels of attractiveness, regardless of age, males chose the more attractive individuals as long term partners.
Relevant discussion may be found on the talk page. Please do not remove this message until conditions to do so are met. September Learn how and when to remove this template message The age disparity between two partners is typically met with some disdain in industrialized nations, and various derogatory terms for participants have arisen in the vernacular. In English-speaking countries, where financial disparity, and an implicit money-for-companionship exchange, is perceived as central to the relationship, the elder of the two partners perceived as the richer is often called a "sugar daddy" or "sugar mama" depending on gender.
The younger of the two is similarly called the sugar baby. In extreme cases, a person who marries into an extremely wealthy family can be labelled a gold digger , especially in cases where the wealthy partner is of extreme age or poor health; this term often describes women but can be applied to either gender. In the latter case, the term trophy is broadened to include any substantial difference in power originating from physical looks, wealth, or status.
It should be noted that the trophy label is often perceived as objectifying the partner, with or without the partner's implicit consent. Where the primary perceived reason for a relationship with a significant age difference is sexual, many gender-specific terms have become popular in English-speaking cultures.
A woman of middle to elderly age who pursues younger men is a cougar or puma, and a man in a relationship with an older woman is often called a boytoy, toyboy, himbo , or cub.
In reverse, the terms rhino, trout and manther a play on the panther term for women are generally used to label an older man pursuing younger women, and the younger woman in such a relationship may be called a kitten or panther.