New research suggests humans have their grandmothers to thank for their monogamous romantic relationships.

University of Utah anthropologist Kristen Hawkes came up with the "grandmother hypothesis," which suggests prehistoric grandmothers are responsible for our long life spans, the University of Utah reported. Now, Hawkes has used computer simulations to demonstrate a link between ancient grandmothers' influence on longevity and human monogamy.

The researcher believes longer human lifespans led to a surplus of older fertile men, which in turn led to the male tendency to guard a female mate from other suitors and "pair bond" with her.

"Pair bonds are universal in human societies and distinguish us from our closest living relatives," Hawkes and colleagues write in the study. "Our hypothesis is that human pair bonds evolved with increasing payoffs for mate guarding, which resulted from the evolution of our grandmothering life history."

The findings contradict past theories that suggest human monogamy developed as a result of males providing food for their mate and her offspring in exchange for ensured paternity.

"[According to the grandmother hypothesis] the key to why moms can have next babies sooner is not because of dad bringing home the bacon but because of grandma helping feed the weaned children. That favored increased longevity as longer-lived grandmothers helped more," Hawkes said.

The new study focuses on whether or not the excess of older males in ancient times had an influence on the nature of modern human relationships. The findings could also shed light on why men like younger women, when the opposite is true for chimpanzees.

"[As human longevity increased there were] lots more old guys, so you have an increasing number of males in the paternity competition, and the only way you can become a father is with a fertile female, which means younger females. So males who had preference for younger females were more likely to leave descendants," Hawkes said.

The findings were published in a recent edition of the journal Proceedings of the National Academy of Sciences.