Unlike any other primate, it is possible that humans live in groups because of the need for predator protection from members of their own species. Although other primates show violence toward their own species, humans are exceptionally good at killing one another. Certainly when driven to extremes like during time ofdraught or on islands where resources are quickly outstripped, humans will attack and eat their own species. Numerous archaeological sites around the world have strong evidence for human cannibalism. Even a 43 Kya Neanderthal site in Spain at the El Sidron Cave shows that several (up to eight) skeletons, who were already victims of poor health and poor nutrition (as evident from the stress lines called "hypoplasias" in their tooth enamel), were butchered, dismembered, and eaten. Cannibalism is not uncommon under duress and is a widespread phenomenon in animals. Human warfare and genocide, however, is uncommon, but can we blame it on our ancestors?
We share an evolutionary history with primates that practice infanticide as a successful adaptation. Male gorillas and gray langurs (Old World monkeys) that are new to a group of females will kill the infants so that they can start their own lineage as soon as possible and increase their own reproductive success.
Our even closer relatives, common chimpanzees are highly territorial. Males patrol perimeters and boundaries and will attack and sometimes kill members of neighboring groups. Chimpanzee society is characterized by male hierarchical relationships which is different from that of bonobos despite their recent evolutionary split just over 2 Mya. While chimpanzees resolve conflict with politics and violence, bonobos ("pygmy" chimpanzees) make peace with love and sex. They have a more female-oriented society where females cooperate unlike chimpanzees. Bonobos will greet rival groups with genital handshakes and sensual body rubs to avoid conflict and if there is conflict, it is resolved swiftly with kissing and sex in various positions between males and females, female and females, and males and males.
Is there anyway of knowing which species best approximates the LCA? Such mental exercises should be undertaken with caution since much less is known about the small populations of bonobos in the wild than about chimpanzees. With increasing field observations of bonobos, it is becoming clearer that the two species are more similar than we once thought. Prior to now, much of the peace-loving behavior of bonobos was known only from captivity where food is always abundant. Furthermore, our tendency to identify with bonobos because of their alleged tendency toward bipedal behavior is now in question since some scientists like Bill McGrew have shown that bonobos and chimpanzees perform equivalent bouts of bipedalism.
Evidence of war or peace from further back in the prehistoric record has been interpreted in various ways. Working among fossils every day it became abundantly clear to Raymond Dart how many parts of the skeleton would make good weapons. Bovid jaws with jagged teeth for cutting, large heavy bones destined for blunt force, fractured long bones that flake like stone and can be as sharp as a stone point are all parts that could and would do serious harm. The abundance of seemingly great weapons at Swartkrans Cave in South Africa led Dart, in his early years during the first half of the 20th century, to speculate that the hominins that lived there had a violent culture. If not to kill prey, they were using the bones of the prey to threaten, maim, or kill one another. This hypothesis came to be known as the "killer ape" hypothesis and their toolkit was named the "osteodontokeratic" culture. The idea lost support through the years with increasing understanding oftaphonomy.
Take away the misinterpreted weapons and australopiths were not particularly threatening. Although they could have been just as strong as chimpanzees, they had much smaller teeth. Plus, there is no direct evidence they were making stone tools until 2.5 Mya (if they were the species making them in the first place). Lacking sharp teeth, size, and technologically advanced weapons, australopiths probably used brains, agility, and social skills to escape from predators. Once overarm throwing evolved and action-at-a-distance was possible, not only could hominins chase away predators and competitors for meat but cheaters (in reciprocal relationships) could be punished with little cost to the punisher (as opposed to using hand-to-hand combat). Throwing, undoubtedly, permitted warfare as well once tool technology, like spear-throwers invented by 30 Kya, enhanced the distance and force applied to projectiles.
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