Human males living with their moms may not expect to have much luck hooking up this Valentine's Day.【C1】______among the northern Muriqui monkeys, males that spend the most time around their mothers seem to get a(n) 【C2】______boost when mating time rolls around. The findings,【C3】______in the Proceedings of the National Academy of Sciences USA, suggest that females in some【C4】______may have evolved to play a critical role in their sons' reproductive【C5】______. Karen Strier, the paper's lead author and a professor at the University of Wisconsin-Madison, says the paper "【C6】______" the socalled grandmother hypothesis, a【C7】______in which human females evolved to live past their prime reproductive years to spend more time【C8】______offspring. The research team observed and【C9】______genetic data from a group of 67 wild monkeys living in a protected reserve in Brazil's Atlantic Forest: infants, mothers and possible fathers. They found that six out of the thirteen【C10】______males they studied spent more time around their mothers than would be expected by chance. These same six monkeys, on【C11】______, reproduced the greatest number of【C12】______. The investigators are still trying to【C13】______why. "It's not until we see moms intervening and helping their sons out," Strier says. "Maybe【C14】______sitting near their moms, they get to see when females are【C15】______active, or maybe they just get more familiar with other【C16】______." The findings can【C17】______with future conservation efforts for the critically【C18】______animals. Strier says, "the【C19】______thing we would want to do is【C20】______a male out of the group where it was born."