Not strict monogamy but humans may be following serial monogamy.
When we speak of monogamy in humans we mean partnership for life, both social and sexual. Whether we humans, as a species, are monogamous by nature? There is no clear-cut answer to that. The topic is much debated and overcrowded with many hypotheses.
Since humans are so similar to chimpanzees, we are often under the impression that we are meant to be promiscuous like them. Any monogamous behaviour seen among us is attributed to either imposed societal restrictions or individual restraint arising out of some indomitable strive to achieve righteousness. In other words, we tend to think, if any of these social and moral restrictions were lifted and we were allowed to be set “free”, we would be no better than apes, or even worse.
Many believe that sexual liberation of the human race would unleash havoc where all our repressed desires take form and we end up with a massive sexual catastrophe. But a little peek at a few statistical reports do not narrate this version of the story. Research says that humans are primarily monogamous. Any species that has shown signs of highly cooperative social behaviour are monogamous by nature, be it insects, birds or mammals.
Before we go into further discussion on monogamy in humans, we must first understand what monogamy means.
What is Monogamy?
The word “monogamy” is derived from the Greek words, ‘monos’ meaning one, and ‘gamos’ meaning marriage. Monogamy refers to the situation where two individuals share an intimate relationship and they live together, share resources, divide labour, produce offspring and take care of their offspring together. The existence of an exclusive sexual relation between two partners, where they do not engage in sexual activity outside their partnership, is also a key characteristic of monogamy.
Monogamy can be of many types. Let’s discuss them one by one.
Genetic monogamy
Occurs when there is no genetic evidence of sex outside the monogamous relationship and all the offspring are produced by the two parents only. In other words all the offspring are full siblings.
Sexual monogamy
An arrangement where a pair share an exclusive sexual relationship without having any sexual partners outside the relationship.
Social monogamy
Social monogamy is an arrangement where two individuals live together under a social setting sharing resources, parenting duties and also having a sexual relationship.
Marital monogamy
Marital monogamy occurs when two individuals are bound together by the sacred vow of marriage. They do not associate in any relationship outside their marriage.
Marital monogamy can be further divided into two categories. They are –
Classical monogamy – Classical monogamy is defined as a relationship where two people come together in marriage as virgins, mate exclusively with one another, produce offspring and turn celibate when either one of them dies.
Serial monogamy – Serial monogamy occurs in a situation when a person is married to only one partner at a time. There can be many partners serially in time but only one partner in a single frame of time.
Monogamy in Humans
Ethnographic studies in pre-industrial and contemporary human societies spread across different regions of the world have shown the existence of polygamous mating systems. Let’s hear what human history has got to say?
Monogamy in human history
A dataset from the Standard Cross-Cultural Sample reveal that polygynous marriages, where a single male gets to marry multiple females, is found in 85% of pre-industrial societies. This particular piece of information was used as a weapon to justify the sexually intensive nature of the human male and argue the legitimacy of a man keeping multiple wives in the modern age. However, closer inspection revealed something even more interesting. While polygyny was accepted, the majority of the population in these societies lived monogamously.
It must be understood that in the pre-industrial societies across the world, which were mostly patriarchal, men controlled much of the wealth. But only a handful of males controlled sufficient wealth to maintain multiple wives. The majority of them had just enough resources to be happily married to one woman.
Marriage signified Monogamy
The sole purpose behind the origin of marriage as a social institution was to give public acknowledgement to who has sexual access to whom. The very institution of marriage warrants sexual fidelity from both partners. When this trust was lost to extra-marital affairs it resulted in separation or divorce, going by legal terms.
Serial Monogamy
Before the advancement of medicinal science, human mortality was high and partners died before the completion of the reproductive period. The surviving individual remarried which resulted in serial monogamy.
When pairs separated by divorce or by free will (seen in some tribal communities), remarried the outcome was also a form of serial monogamy.
Modern contraceptives and sexual infidelity
The advent of modern contraceptives eased the process of sex outside marriage without having the serious repercussion of an extramarital pregnancy. It allowed cheating couples to maintain genetic monogamy without practising sexual monogamy.
For other socially monogamous species there is not much disparity between rates of sexual and genetic monogamy due to the absence of birth control. Extra-pair paternity is low in humans ranging between 0-11% across different societies. This number places humans far ahead of even birds (20% extra-pair paternity) who have a reputation for being exclusively monogamous.
Genetic Monogamy in humans
Genetic relation between siblings is an excellent way to measure genetic monogamy. A study showed that if we just measure the proportion of full siblings in different human societies, humans with 66% full siblings on average, emerge more monogamous than many other known monogamous species. The proportion of full siblings approaches that seen in socially monogamous non-human mammals (70.6%).
Monogamy and Parental Care in Humans
Humans have a long gestation period and the human offspring require parental aid before it could fare for its own in the world. Prolonged periods of parental care is necessary from both parents for the human child to survive which is best achieved under a monogamous arrangement.
Moreover, unlike many other animals human females can be sexually receptive within a few months after childbirth which shortens the gap between two pregnancies. Parental care for multiple children spanning different age groups cannot be handled by a single parent. Under a monogamous arrangement, the biological father and the older children who are full siblings to the newborn (r = 0.5 genetic relation in both) share responsibility with the mother in raising the offspring.
Human fathers provide assistance to their children till the second decade and even third decade of their lives. Only when paternity is confirmed are such helps bestowed on the child. Human parental care being a long affair!
Monogamy and evolution of complex social structures
Monogamy is essential for highly organized social structures to evolve. Complex social networks and wealth accumulation work best when monogamy prevail leading to the development and maintenance of family lineages, a key feature of human societies.
Are humans Monogamous?
Before we go into any claims about the topic we must first etch one thing in our minds that humans are highly intelligent emotionally evolved species. Analysis of any interaction between two individuals of our species should involve the emotional factor as well and not just be weighted by a simple cost-benefit ratio measurement.
But, the pragmatic way to arrive at a rational conclusion involves some tedious observations which must be delved into.
What it’s like in our closest relatives?
To confirm the nature of our mating systems we need to take a quick look at the mating practices and their indicators in our closest relatives – the apes.
Polygamous mating in our nearest relatives, the apes, indicate difference in body size between males and females. The male is much larger than the female and maintains a harem of females. The largest males do 70% of the mating while the rest stay unhappy bachelors. In humans, sexual dimorphism in body size and weight is much reduced with men being just 15% heavier than women. This is indicative of monogamy and matches well with ratios found in monogamous primates like gibbons (Hylobates lar).
Polygamous and promiscous primates have large testes which is indicative of heavy sperm production and multiple copulation. Human testes are much smaller in comparison when adjusted for body size. This further solidifies the claim that humans are meant to be monogamous.
Ovulation in human females are concealed without any visible signal common in chimpanzees and baboons. Concealed ovulation serve to keep information regarding sexual receptivity a secret from males which prevents male versus male competition. Limiting other males from access to such knowledge allows for stable monogamous relationships to develop between a couple.
Fathers care more for their own children
In mammals due to viviparous reproduction or internal gestation mothers are sure of their maternity while fathers can have doubts on their paternity. Paternal investment on offspring is more when paternity is confirmed.
The human child require parental care from both parents to survive better. Monogamy provides the necessary arrangement for the human child to attain optimal parental care from both parents increasing its survival rate and promoting further development.
The emotional appeal of Monogamy is still strong
Humans pair with one another relying on strong emotions. Betrayal from partners take a huge emotional toll on the one who has been cheated on. So, the relationship between a man and a woman and their children does not just rely on fitness benefits, genetic relation and material inheritance but emotional factors as well.
Desire for a lifelong partnership and a happy family is still prevalent in many societies. Even in today’s world with rising divorce rates and cheating becoming a second nature among couples a large section of the young human population (81% of Gen Z) still believes in the concept of monogamy.
Not strict Monogamy but Serial Monogamy may be the trend in humans
Humans are not strictly monogamous but monogamy is the prevalent mode of mating among us. Pre-industrial societies and even some communities in the present world support polygamous mating systems like polygyny and in some cases polyandry, although very rare. But monogamy has been the most common mode of reproduction throughout a large part of human history. If a mating system is to be assigned to humans, Serial Monogamy would be the just one.
