A fascinating study is now explaining why humans have become monogamous. Led by an anthropologist at the University of Utah named Kristen Hawkes, the study suggested that grandmothers have been very important in how humans came to favor long term relationships and monogamy, according to the Northern Californian.

Grandmothers have taken on the responsibility of taking care of young couple's kids, and as a result, these couples had more time for each other. This time led to long term relationships and women being able to bear more children.

Hawkes also came up with the 1997 study "grandmother hypothesis," crediting grandmothers for the long lifespans of humans.

Since more time between husband and wife makes a relationship stronger, the research team posits that grandmothers are vital to the development of pair bonds, a bond which also led to males' tendencies to protect their female partners against competition.

This then led to the development of monogamous relationships, according to Hawkes.

For the recent grandmother study, Hawkes and her team reportedly used computer modelling, which showed that grandmothering also resulted in more number of older and fertile males, according to the Dispatch Times.

Because female fertility drops by 45 and male fertility remains well into old age, the increase in competition led to less success in finding mates. However, it also became relevant to guard their mates.

According to the research team, grandmothers have been the key to human evolution. The study also suggested that grandmothers are the reason why women generally prefer older men.

"The evolutionary importance of grandmothers could also explain why older men are often attracted to younger women," said Hawkes.

"With kids dependent after weaning, grandmothers' help feeding them allowed mothers to have next babies sooner. If a grandmother lived longer, they could help more so their descendants lived longer," she added. "Longer survival swelled the numbers of old males competing to mate with the still fertile females. That male bias in the fertile ages makes guarding a female a more successful way to father offspring than continually seeking another mate."

"The grandma hypothesis counters that the reason that females are able to have babies earlier is not because of the male providing for them, but because the grandmothers help feed weaned children, which helped increase longevity," Hawkes also said.

The grandmother study was published in the journal Proceedings of the National Academy of Sciences (PNAS) Monday, reported Red Orbit.