Many authors criticize lifelong sexual monogamy as unnatural and unrealistic. They contend that humans have never been a sexually monogamous species, and that cultural expectations of sexual monogamy place enormous burdens on individuals to fulfill all the sexual needs of their partners. These expectations are quite unrealistic given how much variety exists in people's sexual desires and sex drives. In addition, sexual desires and sex drives can change over time due to circumstances (e.g., periods of high stress or poor health) and due to normal aging (e.g., changes in hormonal levels). Loving partners can find themselves mismatched in terms of their current sexual desires or sex drives. The failure to live up to unrealistic expectations of lifelong sexual monogamy causes people needless suffering.
"Currently, monogamy is the only lovestyle style considered legitimate by our culture, even though the evidence clearly indicates that humans are not monogamous by nature. The reality is that the majority of husbands and wives have extramarital affairs and often get divorced as a result. In fact, one form of polygamy, often called serial monogamy, is now the most common form of relationship found in our culture. But divorce and remarriage are extremely stressful for children as well as their parents. Might there not be a better way? "
"Monogamous couples are completely dependent on each other for affection and sex; and many become dissatisfied due to sexual incompatibilities, differences in level or frequency of sex, boredom with their sexual patterns. When they feel strong sexual attractions towards others they must repress these feelings or end their current relationship in order to have sex with someone else. Many complain bitterly that although they love their spouse and feel strongly attracted to him or her, the spouse doesn't want sex frequently enough or does not enjoy the same sexual activities. This leaves one partner always wanting more sex or more variety in sexual practices, and the other always feeling pressured for sex, often resulting in one partner having secret affairs with other lovers to fulfill their sexual needs.
Research supports the claim that lifelong sexual monogamy is unnatural and unrealistic. Biologists have strong evidence that social monogamy is rare among animals, and that sexual monogamy is even more rare, as most socially monogamous species are not sexually monogamous.
It would be somewhat odd if people were sexually monogamous for life; Then again, people do many odd things in comparison to other animals. The fact that 80-85% of societies allow polygynous marriage further argues against the idea that sexual monogamy is built in to human nature.
Studies of extramarital affairs and divorce provide evidence that lifelong sexual monogamy is unrealistic. Substantial numbers of people engage in extramarital sex.About half of married people in the United States divorce, and the majority of divorced people find new partners and marry again.Many people, perhaps the majority, simply do not live up to the expectation of lifelong sexual monogamy.