Many relationships, especially in Western societies, are considered monogamous, but not all couples are equated with this term. Etymologically, “monogamy” is a Greek word meaning the act of marrying only once in a lifetime, but in practice there is much confusion about what the term means and how to properly use it. This is true even in scientific fields that study the social behavior of animals.
Let’s imagine that two mice live their entire lives together and have an emotional bond, but they have sex with other mice. Or two solitary fish breed only once in their life and only with the same individual. Should we consider these animals monogamous? What exactly defines monogamy?
For much of the 20th century, the scientific community assumed that most birds were monogamous, as 90% of species formed pairs. Women were believed to be faithful. Scientists have only rarely documented cases of forced mating, where another male goes to the nest of a mated female and forces her to have sex. This behavior is consistent with the widely accepted hypothesis of parental investment. According to proponents of the theory, women are more selective than men when it comes to sex because they must expend more energy on reproduction. So, scientists believed that female birds are passive and it is up to males to actively seek sex.
Such ideas coincide with modern concepts of women. For example, in Desmond Morris’s influential 1967 book Naked Monkey, he described the woman in hunter-gatherer societies as a monogamous creature who happily waits for her man to return from hunting in order to satisfy her sexually. In fact, Morris argued that the female orgasm first emerged to strengthen the bond between couples.
Dissenting voices soon questioned the idea of a submissive and monogamous woman, notably feminist scholars such as Sara Hardy and Patricia Gowaty. The latter was studying bluebirds (Sialia cialis), was considered monogamous. In an interview, Gowaty says that early in his career, in the 1980s, he saw women actively cheating. “Women will take off in the middle of the night and fly a mile away,” he said. When he informed his colleagues, they refused to accept what he was saying; this was not the behavior of female birds. Nevertheless, he finally managed to acknowledge the research results; In 1984, he published the first paper questioning the sexual passivity of female birds.
Today, we know that infidelity occurs daily in bird pairs, by both males and females. Indeed, according to a 2002 study, 11% of offspring are “the result of extra-pair paternity.” There are several hypotheses that attempt to explain the evolutionary advantages of a female breeding with a male who is not a common mate. According to one theory, the behavior allows the female to maximize genetic diversity among her offspring. Another hypothesis is that this allows her to take advantage of the opportunity to breed with a male who may have better opportunities than her mate. Whatever the reason, sexual exclusivity is so rare in animals that scientists have finally come to define what they mean by social monogamy, which does not necessarily mean sexual monogamy.
However, it is not just about distinguishing between social and sexual monogamy. The reason there is so much confusion about this topic is that monogamy is not a single feature; rather, there are different ways to be monogamous. In some species, husbands and wives participate equally in caring for offspring, while in others, couples have unequal roles; some always live together, and some only intermittently. Some mate for life, others only for one season; some are jealous and some are not; most show affection, while others only procreate.
Even among primates, there are differences. For example, the Masoala hook-eared lemur (Phaner furcifer) is a nocturnal primate from Madagascar; these animals form pairs and live together in the same area. Males actively defend the territory. Couples are very stable and usually last more than three years. However, men and women rarely have sex; when they do, they show little interest in each other, or worse, the dates aren’t friendly. Females are dominant and often fight for food, while males avoid conflict. Their communication is limited to distant voices and sexual encounters. It is a union with no emotional attachment.
This is very different from the monogamy of marmosets, where the affective bond is so strong that the animals have been proposed as a model for studying sentimental bonds between humans. They tend to stick together to eat and move, attack individuals who might threaten their bond, become stressed when separated, maintain sexual exclusivity, raise their young together, and even nest their tails together. Marmosets are one of the very few species that combine various aspects of monogamy.
As with animals, monogamy varies among humans. Some people live together but have sex with other people. Others have children from the same individual, but fall in love with more than one person at the same time. Some people raise their children together, but there is no romantic relationship. So, when can we talk about monogamy? To avoid confusion, perhaps it is more useful to talk about cohabitation, sexual exclusivity, co-parenting and love.