Research in recent years has focused on chimpanzees and other monkeys who murder their own. Field studies in TanzaniaÂ have demonstrated that chimpanzees will attack and kill other chimpanzees, and brutally so.
In one study (that took place over a five-year period), a group of male chimpanzees directed attacks on a splinter group of chimps that had broken away from the larger group.
Each member of this splinter group was beaten and subsequently died. Young male chimps initiated these attacks, usually using their hands, feet and teeth, though sometimes stones were thrown, as well.
A study of langur monkeys illustrates the same principle at work, that of intra-tribal warfare, instigated by outcast young males.Â
The langur monkey lives in a society in which an alpha male dominates and is surrounded by numerous female langurs, all of whom bear his offspring and live in obeyance to the alpha male.
The alpha male drives off the younger male langurs from the commune; in time, some of the young males return to challenge the hierarchy of the alpha male, by mocking and attacking the leader of the 'pack.'
If the alpha langur is successful in fighting off his young aggressors, his society will remain intact and the young males will be driven off, forced to find new females of their own.
If the alpha langur is not successful, the young males then take over the troop, and systemically and brutally killÂ infant langurs, smashing them against the trees, crushing their skulls, until all infants are dead.
The young female langurs in the troop remain unhurt, as they are the love object of the young males.
The young males then begin to seat themselves at the head of their own helm, to take many females who will then bear offspring only to them.
Biologically, it is important for the band of marauding young males to to kill the infants, because the infants are preventing the females from bearing new young.
The females are suckling the infants, and by so doing, are incapable of having new infants.
As long as the female langur is nursing an infant, she is not menstuating and remains infertile with either her alpha male or with a newcomer.
For the newcomer male langurs to establish themselves, they must secure the sexual interest of the females.
Once the nursed infants are dead, the female langur begins to menstruate again and she becomes receptive to the young males who have just murdered all her children.
Numerous comparisons between such primate murder and humans has been drawn, likening this kind of biological determination to human stepfathers who are more likely to abuse their stepchildren.
But we can rise above such biological determinism, despite tendencies we as a species may have.