Correspondingly, monogamy and commitment are more commonplace.
On the other hand, when people live within environments that encompass little stress and threats to the viability of offspring, the need for serious and committed relations is lowered and therefore promiscuity and infidelity are more common.
It is more common for men compared to women to engage in extradyadic relationships.
The National Health and Social Life Survey found that 4% of married men, 16% of cohabiting men, and 37% of dating men engaged in acts of sexual infidelity compared to 1% of married women, 8% of cohabiting women, and 17% of women in dating relationships.
One measure of infidelity is covert illegitimacy, a situation which arises when someone who is presumed to be a child's father (or mother) is in fact not the biological father (or mother).
Frequencies as high as 30% are sometimes assumed in the media, but research Such studies show that covert illegitimacy is in fact less than 10% among the sampled African populations, less than 5% among the sampled Native American and Polynesian populations, less than 2% of the sampled Middle Eastern population, and generally 1–2% among European samples.
According to this theory, an area has a high sex ratio when there is a higher number of marriage-aged women to marriage-aged men and an area has a low sex ratio when there is more marriage-aged men to marriage-aged women.
Strategic pluralism is a theory that focuses on how environmental factors influence mating strategies.
According to this theory, when people live within environments that are demanding and stressful, the need for bi-parental care is greater for increasing the survival of offspring.
Depending on the context, men and women can experience social consequences if their act of infidelity becomes public.
The form and extent of these consequences are often dependent on the gender of the unfaithful person.
Support for this theory comes from evidence showing higher divorce rates in countries with lower sex ratios and higher monogamy rates in countries with higher sex ratios.