A shortage of female mates appears to impact willingness to engage in uncommitted sexual relationships, according to researchers from the University of Glasgow.

Expanding upon previous research, study authors Michal Kandrik, Benedict Jones, and Lisa DeBruine used multi-level analysis to examine how regional differences play a role in men and women’s mating strategies based on the scarcity of female mates.

The online study involved 3,209 heterosexual women and 1,244 heterosexual men. The Revised Sociosexual Orientation Inventory was used to assess individual differences in disposition to engage in uncommitted sexual relationships; sociosexual subscales focused on differences in behavior, attitudes, and desires.

Additional data from the U. S. Social Science Research Council provided information from all 50 states and Washington, DC and were used to evaluate regional differences; these data included adult sex ratio, fertility rate, teenage pregnancy rate, women’s age at first marriage (used to measure scarcity of female mates); the human development index, gross domestic product per capita (used to measure wealth); infant mortality rate, percent of low-birth-weight infants, life expectancy at birth, and percent of children (under 6 years of age) living in poverty (used to measure environmental demands).

Researchers were particularly interested in examining the possible relationships between sociosexual orientation and regional variation in the shortage of female mates, environmental demands, and wealth. Results revealed that only one factor—scarcity of female mates—predicted differences in men and women’s global sociosexual orientation, specifically, “participants in states where female mates were particularly scarce reported being less willing to engage in uncommitted sexual relationships.” Of additional interest were findings from the three sociosexual subscales—attitude, desire, and behavior.

The researchers noted that a shortage of female mates predicted scores on both the attitude (e.g., “Sex without love is OK.”) and desires (e.g., “In everyday life, how often do you have spontaneous fantasies about having sex with someone you have just met?”) subscales, but not the behavior subscale (e.g., “With how many different partners have you had sexual intercourse on one and only one occasion?”). Given that behavior can be more restrained than attitudes and desires, these findings support previous research that “regional differences in sociosexual orientation reflect psychological adaptations evoked by the local environmental conditions.”

The study authors provide an interesting link to their results with other research of bird species, noting that “across bird species, pair bonds are more stable when sex ratios are male-biased. Together, these results suggest that scarcity of female mates can have similar effects on mating strategies in diverse taxa.” Kandrik and his colleagues advocate that additional research investigate the causal associations “among regional differences in the scarcity of female mates, individuals’ sociosexual orientations, and regional differences in cultural norms and values, such as anti-promiscuity morality,” a position also favored by other researchers.

The study, “Scarcity of Female Mates Predicts Regional Variation in Men’s and Women’s Sociosexual Orientation Across US States” was published in the May 2014 issue of Evolution and Human Behavior.