Science has yet to definitively pronounce on whether humans are naturally monogamous (lifelong male-female breeding pair) or polygamous (single male breeding with more than one female). The human male body provides ambiguous clues to the answer but the balance of evidence indicates that we are biologically inclined towards monogamy while retaining an urge to "sleep around". A nicely written summary of this field was written by David Engber in Slate – published on October 9th, 2012.
Consider testicl* size as an indicator of mating habits. Male chimpanzees compete with each other to have sex with as many female chimps as possible. A female chimp’s uterus at any given time will contain sperm from several males. If any particular male is to have a chance of impregnating a female, he must ejacul*te lots of sperm many times a day and this calls for big cojones. Chimp testicl*s routinely weigh 150 grams to 170 grams, one third the weight of the chimp brain. On the other hand, humans have evolved relatively small testicl*s, maxing out at about 50 grams (3 per cent the weight of human brain). Human testicl* size points towards conservative sexual habits.
Clue
Male to female size ratio (sexual dimorphism) in a species is also a clue as to whether monogamy or polygamy is practised. The bigger the gap in size between male and female, the greater the competition among males for access to females. For example, male gorillas are much bigger than females and polygamy is the rule. The dominant male in a gorilla group services a harem, hogging all the sex with all females in the group and denying the subservient males any “look-in”. The dominant male’s sperm doesn’t have to compete with other male sperm and so the gorilla has evolved relatively small testicl*s. Based on this gorilla pattern the relatively small human testicl*s point towards polygamy.
Considering his massive body size, the male gorilla has a surprisingly small erect penis, on average 6.4cm long. The average erect human penis on the other hand is 15.2cm long. However, if you look across the entire primate range, the human penis size is not remarkable – one baboon one third of human weight has a penis almost as long as the human penis. Twenty-nine per cent of primates are monogamous but human penis size does not point emphatically towards monogamy.
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Penis configurations across primate species are generally much more interesting than the human penis. The penises of other primate species commonly have lumps, ridges, kinks, spines or flanges, whereas the straight and smooth human penis lacks such features (unless you are rather unfortunate!). Bland characters such as the human penis are usually found in monogamous animal species.
Also, DNA studies of male to female breeding ratios in hom*o sapiens indicate about two women to every procreating man. This ratio is within the range for societies described as monogamous.
Monogamous habits
Paleontologist Owen Lovejoy has published evidence (Science, October 2nd, 2009) that human changeover to mostly monogamous habits occurred with our ancestor Ardipithecus ramidus, who lived 4.4 million years ago. Ardipithecus walked on two legs, freeing the hands, thereby allowing males to carry food to females. One can conjecture that females would favour males who offered them food, indicating how natural selection could introduce monogamy. And monogamy offered an obvious attraction to lower-ranking males. Monogamy is also a much more energetically economical arrangement than polygamy which is wasteful of time and energy as males fight over females.
Engber also describes cultural reasons to explain why monogamy became the norm. Polygamy tends to cause social problems, leaving many angry men without wives and inclined to behave in risky ways. This increases conflict and lowers productivity. A preference for male babies in China distorted the natural male to female societal ratio. In the period 1988 to 2004, the number of unmarried man doubled and so did crime.
In the modern human world monogamy is far more widely practised than polygamy. Polygamy is legal in 58 out of almost 200 sovereign states; the great majority being Muslim countries in Asia and Africa, but polygamist marriage is not recognized in the rest of the world. I don't think polyandry, where one woman has more than one husband, is legally recognised anywhere.
William Reville is an emeritus professor of biochemistry at UCC
FAQs
We are termed 'socially monogamous' by biologists, which means that we usually live as couples, but the relationships aren't permanent and some sex occurs outside the relationship. There are three main explanations for why social monogamy evolved in humans, and biologists are still arguing which is the most important.
Is it natural for a man to be polygamous? ›
To begin, it is important to clarify that polygamy is not a gender trait. There is no biological or scientific programming in a typical man or woman that inherently drives them to seek multiple sexual partners.
How common is monogamy in nature? ›
Scientists now estimate that only about three to five percent of the approximately 4,000+ mammal species on Earth practice any form of monogamy. Before the advent of DNA fingerprinting, scientists believed that about 90 percent of bird species were truly monogamous.
Is monogamy natural or a social construct? ›
Even though many people may accept monogamy as the standard relationship style, viewing it as a social construct rather than an innate need may help us understand the diverse ways in which people may actually manage their romantic lives today.
Are men biologically polygamous? ›
Polygamy is not the desire for more partners. Men are not naturally polygamous, neither is a woman. Everyone desires more. Interestingly, polygamy only does apply to the married — a bachelor(rette) or a person in a monogamous marriage can't be polygamous — if anything, you're promiscuous.
Do humans have a biological imprint of polygamy? ›
We also carry the biological imprint of polygamy, the opposite of lifelong fidelity to one mate. Polygamy is divided into two categories: Polygyny, in which a man has more than one wife, and polyandry, in which a woman has more than one husband.
Do men prefer monogamy or polygamy? ›
About one-third of 18- to 44-year-old men (35%) prefer complete monogamy over complete non-monogamy (9%), while 46% want something in-between.
Were ancient humans monogamous? ›
By about 3.5 million years ago, however, the finger-length ratio indicated that hominids had shifted more toward monogamy. Our lineage never evolved to be strictly monogamous. But even in polygamous relationships, individual men and women formed long-term bonds — a far cry from the arrangement in chimpanzees.
Did humans evolve to be polygamous? ›
Acknowledged evolutionists and anthropologists discovered that human beings evolved in a regime that was often polygamous. In fact, 80 percent of early human societies were polygamous.
Were Native Americans monogamous? ›
It could be monogamous or polygamous, endogamous or exogamous between different tribes for expansionist purposes, as well as matrilineal or patrilineal, based on agreements between families with a strong clan sense. For them, arranged marriages with the bride's consent also existed.
The answer is simple: being monogamous is not as realistic as everyone thinks. This isn't to say that monogamy isn't possible, but rather that it isn't likely in a relationship meant to last a lifetime.
Which gender is more monogamous? ›
Given the pref- erential mating strategies dictated by evolutionary theory, it would be expected that men would not value their own sexual monogamy highly, even when they value their partner's sexual monogamy. Indeed, women were found to value sexual monogamy more than men.
Is monogamy unnatural for humans? ›
This “pair bonding” is one reason that monogamy—including lifelong monogamy—is at least possible for humans, even if it doesn't spring naturally from our biological makeup. Recall that even in polygamous societies, many end up monogamous anyway: It's a possibility evolution had to deal with.
Is monogamy nATURAL or cultural? ›
Despite the human ability to avoid sexual and genetic monogamy, social monogamy still forms under many different conditions, but most of those conditions are consequences of cultural processes. These cultural processes may have nothing to do with relative reproductive success.
Is polyamory nATURAL? ›
“nATURAL” HUMAN
Franklin Veaux, author of More Than Two: A Practical Guide to Ethical Polyamory, argues that humans are naturally polyamorous, naturally monogamous, and naturally asexual.
What percentage of people are polyamorous? ›
While studies indicate that only about 5 percent of Americans are currently in polyamorous relationships, growing interest and acceptance of the practice could damage a broad range of relationships and families.
Were neanderthals monogamous? ›
Humans are broadly monogamous, so the researchers suggested that there might be a link between a species' digit ratio and sexual strategy. If they are right, Neanderthals – who had ratios in between the two groups (0.928) – were slightly less monogamous than both early modern and present-day humans.
When did the Bible switch to monogamy? ›
As Christianity emerged in the Roman Empire in the first centuries AD, it embraced monogamy and took it further, insisting that two people must reserve their bodies and desires for each other, marriage becoming 'an everlasting threesome with God'.
