Monogamous owl monkeys produce 25 percent more children over a decade than those having more than one partner, finds a new study.

Owl monkeys are known to live in monogamous groups that have an adult male, female and their offspring. Young children move out of the group at the age of 3 or 4. There are also "floater" individuals that attack the male of the pair-bonded couple and replace him as a mate and infant-care provider. The presence of "floater" individuals was first reported in 2008 by researcher Eduardo Fernandez-Duque and his colleagues from University of Pennsylvania.

The same research team has now found that the owl monkeys that stick to one partner produce more offspring than those with more partners. The team has been observing 18 owl monkey groups (a total of 154 monkeys) and collecting data over the last 16 years in a portion of Argentina's Chaco region.

Researchers noticed that the disruption caused to pair-bonded couples by male and female floaters is a common occurrence. They documented 27 female and 23 male replacements in the groups they observed. The replacement involves fights that become fatal for the evicted individuals.

Based on observations, the research team found that the monkeys having one partner produced 25 percent more offspring per decade than those with two or more partners. "What we're showing is that if you manage to stay with the same partner you produce more infants than if you're forced to change partners," Fernandez-Duque said in a statement.

It is not yet clear as to why the reproduction rate reduces in monkeys having more partners. One possibility researchers suggest is the delay in reproduction, as female owl monkeys in Argentina typically only conceive between March and May. The delay could possibly occur as the two individuals take time to get to know each other before reproducing and giving commitment to infant care.

The study suggests that the evolution of pair bonds might have improved reproductive fitness in the species. This could also shed light on why monogamy emerged in humans, reports LiveScience.

"There's some consensus among anthropologists that pairs-bonds must have played an important role in the origin of human societies," Fernandez-Duque said. "Call it love, call it friendship, call it marriage, there is something in our biology that leads to this enduring, emotional bond between two individuals that is widespread among human societies."

The findings of the study are published in the journal PLOS ONE.