Sarah Hrdy is an American anthropologist who has devoted much of her career to studying parental care in primates. She made major contributions to evolutionary psychology and sociobiology and has been selected as one of the 21 “Leaders in Animal Behavior”.
In her one of her first books, The Langurs of Abu: Female and Male Strategies of Reproduction (1977), she described the langurs as practicing infanticide. That description led one (male) colleague to snipe,
“Sarah Hrdy’s monkeys are deranged.”
Hrdy had seen male langurs attack and kill infants sired by rivals, so that they could induce estrus in the females and then mate with them. Female langurs had their own defenses against marauding males. When a male took over a troop, pregnant females would fake being in estrus and let him mate with them. The male would then believe himself to be the father of her offspring and protect them accordingly.