Understanding XMMs and sugar daddies using evolutionary principles

Yeo Shen Yong
5 min readJan 22, 2022
taken from https://www.gq-magazine.co.uk/article/rules-older-men-dating-younger-women

Today, couples with the male older than the female counterpart is a common occurrence. A famous example involves a controversial US president Donald Trump and his wife Melania. The duo share an age gap of a great 24 years, leading to some snide remarks of him being a ‘sugar daddy’. A sugar daddy, being a rich and usually older men who buys presents for or gives money to a younger person, especially a woman, usually so that the younger person will spend time with him and have a sexual relationship with him, is actually not uncommon at all, although people tend to be hesitant in throwing the phrase around, because of the negative connotations bound to it. On the other hand, you have the sugar babbies, who are typically much younger females. In Singapore, a common slang used to describe them would be 小妹妹 (xiaomeimeis, or XMMs, for ‘small girls’), again another derogatory term not be used loosely.

But have you ever wondered why aren’t there as many sugar mommies, or 小弟弟 (‘small boys) around? Beyond that, looking at marriage statistics in Singapore, you will find that the median age of first time marriages for brides is consistently about 2 years older than grooms.

Median age of first time marriages in Singapore from 2011 to 2020, by gender, taken from https://www.statista.com/statistics/625108/median-age-of-first-time-marriages-in-singapore/#:~:text=As%20of%202020%2C%20the%20median,Singaporean%20women%20in%20delaying%20marriage.

Why is this so? Some would point out the fact that mandatory national service in Singapore results in Singaporean males entering tertiary education two years later than females, or attribute it to other cultural reasons, but in fact, the main causative factor is evolutionary in nature.

Mate Preference of Males

From a biological and evolutionary perspective, males and females play a very different role in a sexual relationship, and hence adopt different strategies to find ideal mates for reproduction and passing down genes to the next generation. Males look for females who are fertile and hence better able to bear children for them, which directly benefits the male as he is able to pass down his genes to the next generation.

Age is a critical factor when it comes to a female’s fertility. On average, females are most fertile at the ages of 20–24, dropping to 85% fertility at 30–34 years and subsequently to nearly 35% at age 40–44 and then 0% at age 50. Males, however, do not share the same characteristic, as their fertility reduces much less drastically, being 90% fertile at age 45–50 and 80% for those over 55 (Pawlowski, 2000). From an evolutionary standpoint, males would have come to understand and recognise this, hence formulating a strategy to look for females which look young and hopefully are young to bear their children.

Besides age, other physical factors such as beauty and waist-to-hip ratio also influence male mate preference, with beauty indicating good genes and a low waist-to-hip ratio indicating that the female is not pregnant and hence able to bear children [To understand the full picture, I recommend reading my previous article, Sorry Twice, But Love Is Actually a Science].

Mate Preference of Females

When evaluating a potential mate, females tend to look for someone who is able to take care of the offspring in the long term. The traits which are related to that include resource holding potential, which refers to an individual’s financial and occupational status, as well as a more qualitative trait domestic virtue, referring to how capable the individual is in fulfilling his domestic responsibilities, which is largely not related to finance.

In general, an individual’s income and hence resource holding potential increases with age for most societies around the world. Take the table below for example, which shows the median gross monthly income for the populations under different age groups. Notice how monthly income increases and then peaks at the age group of 40–44.

A table showing the median gross monthly income from work in Singapore for different age groups. Taken from https://dollarsandsense.sg/earning-much-peers-much-average-salary-singapore-every-age-group/

Resultingly, an older male actually fits the bill for an ideal partner most of the time, simply because he will likely be better able to support the household as compared to younger males. Of course, in reality, there are many other factors which influence mate preference for both males and females, but age has always been a powerful one (Bereczkei 1997).

Interestingly, females who are confident in their physical attractiveness are more demanding on requirements for potential mates, and males who are more resource-rich likewise want a more attractive partner. The evidence highlighting the constant evolutionary game between individuals of the two sexes is indeed fascinating.

Cultural and Environmental Influences

The age gaps in sexual relationships between males and females of different population varies based on cultural and environmental influences. In several countries in Sub-Saharan Africa, for example, which are largely third-world, poorly developed countries, age gaps in many of the countries could be higher than other regions around the world, with a Singulate Mean Age Marriage (SMAM) difference of up to 9 years, which is the the difference in average age at first marriage between men and women. This is because these countries are plagued with pathogens and diseases, which increases the use of polygamy, in particular polygyny, where one male mates with many females, in these societies (Low 1990). The use of polygyny allows males to produce offspring with a diverse range of alleles, increasing the chance for an offspring to survive and continue propagating their genes. Polygyny, in turn, tends to increase the average age gap of sexual relationships, because of the increase in intrasexual competition between males (due to the reduction of the number of females available for mating), hence males value younger females for their higher reproductive value.

However, as communities around the world become increasingly modernized, spousal age gaps are diminishing with it. As more women are working nowadays, the notion of having the male figure in the household be the sole breadwinner is rather outdated. Traditions of the past, which are a result of evolutionary pressures are being challenged today, and people can generally exercise more freedom of choice. In many cases, gender roles in a family are reversed, and having a bride older than the groom is not an uncommon occurrence.


The human race has come such a long way from our humble beginnings, and I find it interesting to see how our evolution has shaped our behaviors today. It is important to remember that we are not defined as who we were, and are not obliged to act as our ancestors did, as the environmental pressures from the past are different from they are now. As they say, love knows no boundaries, so be free to choose who you fall in love with.


Pawłowski, B. (2000). The biological meaning of preferences on the human mate market.

Tamas Bereczkei; Silvia Voros; Agnes Gal; Laszlo Bernath (1997). Resources, Attractiveness, Family Commitment; Reproductive Decisions in Human Mate Choice. , 103(8), 681–699. doi:10.1111/j.1439–0310.1997.tb00178.x

Low, B. S. (1990). “Marriage systems and pathogen stress in human societies”. American Zoologist. 30 (2): 325–340. doi:10.1093/icb/30.2.325.



Yeo Shen Yong

Critically analysing life a lot more than I should.