Receiving severe aggression correlates with fetal gender in pregnant pigtailed monkeys

Pregnant females were severely bitten in 220 of 2,822 conceptions among pigtail macaques living in harem groups. These pregnancies yielded 58.6% female offspring compared with 48.5% for nonbitten pregnant animals. The fetal gender difference occurred only after midterm, reaching a peak of 70% female fetuses in the 4th gestational month. Fetal gender thus appeared to influence maternal behavior, appearance, or physiology in some way detectable to other monkeys with the consequence of altering risk for receiving severe aggression.