Monogamy refers to the norm or condition of a single male mating with a single female by forming a “pair bond,” with both defending territory and caring for the young. The need to care for the young necessitates many of the species to enter into monogamous relationships. For example, monogamous male parent birds care for the young by watching for danger (willow ptarmigans) or defending a territory with a nest cavity (eastern bluebirds), whereas his mate collects the food to feed the offspring. Male birds are involved further in most passerines, where they feed brooding females and/or help to feed the young. In herons, egrets, some woodpeckers, and others, males not only provide food for the young but also share in incubation. On the contrary, for species whose males contribute little or nothing to rearing the young, females are very choosy in selecting the best mates. Males of these species compete to be chosen and are not themselves choosy. Females of these species, because of their biological ability to produce only a limited number of offspring, prefer mating with only the best males. From the male point of view, mating many times and with many females increases the chances of producing surviving offspring. Therefore, males must invest their energy to make themselves more attractive and appealing to as many females as possible. For example, the magnificently tailed peacock’s elaborate train does nothing to enhance survival but is necessary for attracting mates.
The monogamous “bond” may vary from a single season to a lifetime. For example, most of the birds seem to form a monogamous bond that lasts from as short a period as single nesting (house wrens) to as long as a lifetime (albatrosses, petrels, swans, geese, eagles, and some owls and parrots). In a similar fashion, many monogamous animals pair for a season, but some (e.g., gibbons) pair for a lifetime.
During recent years, many ornithologists and behavioral ecologists began to view monogamy as part of a “mixed” reproductive strategy, that is, where matings may occur outside the primary pair bond but both members of the pair still contribute substantially only to the care and feeding of the young from their own nest. Some species are viewed to be “facultatively” monogamous; that is, they are monogamous due to certain environmental constraints. Once these constraints are removed or altered, they would typically exhibit some other form of mating system such as polygyny (one male mating with more than one female) or promiscuity (mating without forming pair bonds). For example, North American dabbling ducks are considered to be monogamous only due to the inability on the part of males to monopolize more than one female. These ducks breed synchronously, and their populations typically contain more males than females.
Prairie voles (Microtus ochrogaster) are among a select 5% of mammals that are habitually monogamous. Once they have mated, the males “fall in love” and stay close to their partners, protecting them, helping them raise offspring. Their close cousins, the meadow voles (Microtus pennsylvanicus), however, mate with multiple partners and pay little attention to subsequent offspring. When researchers alter the behavior of meadow voles by manipulating a single gene—vasopressin receptor—meadow voles become as monogamous as prairie voles.
Among human populations, monogamy stipulates that a man can marry only one woman at any one time in his life. It is essentially a social norm or a cultural custom. Even though various forms of marriages have been practiced through the generations, monogamy has emerged to become law in some countries today, such that the legal registration of more than one wife becomes a violation. Nonetheless, there are still several nations that prefer polygamy. For example, a worldwide ethnographic survey of 849 human societies showed 708 whose customs are polygynous (more than one wife), 4 whose customs are polyandrous (more than one husband), and 137 whose customs are monogamous. Even among those monogamous societies, a considerable number of married men and women tend to have sexual relationships with individuals outside their marriages. In her study on Adultery, Annette Lawson noted that various researchers arrived at a general consensus that (a) approximately one quarter to one half of married women have at least one lover after they are married in any given marriage and (b) married men stray more often than married women—perhaps 50 to 65% by 40 years of age. Similarly, Maggie Scarf thought that most experts estimate some 50 to 65% of husbands and some 45 to 55% of wives to be extramaritally involved by 40 years of age. Peggy Vaughan echoed that 60% of men and 40% of women are likely to have extramarital affairs. The significance of these figures is even higher when the total number of marriages involved is considered because it is unlikely that all of the men and women having affairs happen to be married to each other. Vaughan observed, “If even half of the women having affairs (or 20 percent) are married to men not included in the 60 percent having affairs, then at least one partner will have an affair in approximately 80 percent of all marriages. With this many marriages affected, it’s unreasonable to think affairs are due only to the failures and shortcomings of individual husbands or wives.” Therefore, these scholars argue that the irony of the “monogamy myth” (a belief system that most people are monogamous and that only a few “bad” or “weak” people have extramarital affairs) is that it prevents societies from dealing with the issues that need to be addressed to make monogamy a more attainable goal for everyone.
Some studies suggest a new term, serial monogamy, to denote the practice of restricting sexual contact to a single partner (married or not) for a limited period of time and then ending that relationship before beginning another (although in practice there may be a brief overlapping time period). On the other hand, some have broadened the scope of the term monogamy to mean confining a sexual relationship to one other person even in the absence of a legal status of marriage (e.g., an unmarried heterosexual couple, a homosexual couple in a jurisdiction that does not recognize marriage between homosexual persons). Monogamy in this sense is recommended by health professionals discussing safer sex practices.
- Ehrlich, P. R., Dobkin, D. S., & Wheye, D. (1988). The birder’s handbook: A field guide to the natural history of North American birds. New York: Simon & Schuster.
- Lawson, A. (1989). Adultery. New York: Basic Books.
- Lim, M. M., Wang, Z., Olazabal, D. E., Ren, X., Terwilliger, E. F., & Young, L. J. (2004). Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene. Nature, 429, 754-757.
- Scarf, M. (1987). Intimate partners. New York: Random House.
- Vaughan, P. (1989). The monogamy myth. New York: Newmarket Press.