The killer ape theory or killer ape hypothesis is the theory that war and interpersonal aggression was the driving force behind human evolution. It was originated by Raymond Dart in the 1950s; later it was developed further in African Genesis by Robert Ardrey.
According to the killer ape theory, the ancestors of humans were distinguished from other primate species by their greater aggressiveness. Furthermore, according to the theory, this aggression remains within humanity, which retains many murderous instincts.
The theory gained notoriety for suggesting that the urge to do violence was a fundamental part of human psychology, but is not widely accepted among anthropologists today. The hunting hypothesis is often associated with the theory, because of similarities and because Robert Ardrey has developed both.
The expression killer ape does not mean an outstanding aggressive kind of ape, in fact the term is about the anthropological analysis of human aggression. It is scrutinized whether present-day behavior like e.g. the defense of one’s own piece of land, palpability or even murder base on ancestors of humankind. Accordingly, the killer ape is a notably belligerent species on which our instincts might be rooted, because this very ancestor could establish itself due to its special aggression.
As founder of this thesis, Raymond A. Dart (1893-1988) dealt with this issue in his professional article “The predatory transition from ape to man”, 1953.
The title is misleading; contrary to popular belief, humans did not, in fact, evolve from today's modern apes - humans and modern apes split off from a common ancestor, who was an archaic species of ape such as Dryopithecus.
The predatory transition from ape to human
The step from ape to human
The question is what exactly could cause the evolutionary step from ape to human. Basically, there are three different versions: the increase of the brains’ size, the acquisition of speech or the upright motion. Smith excludes this last option; otherwise the traditional erect gibbon would be a possible ancestor of humans. For him, the relevant point was the bigger brain. It would have made the bipedal movement possible and would have accelerated the enlargement through common use of its hands, which are no more needed to walk.
The "Taung Child"
This approximately 2.5 million year old cranial bone, also known as “Taung Child”, was a first proof of bipedal apes. Robert Broom (1866-1951), primarily a Scottish physician, who spent his life as an archeologist in Australia since 1892, agreed to this statement, too. Five years later he decided to spend the rest of his life in South Africa. His excavations from 1946 pointed into the same direction, when he also discovered bones from the Australopithecus africanus.
However, further examinations showed that, in these cases, the size of the brain was not to be equated with the evolution’s level. In fact, it is much more popular to connect the accomplishment of more and more complex movements directly with an evolutionary response, which caused the brain to grow.
Both Dart and Broom, as well as Charles Darwin (1809-1882), agreed that this new type of locomotion brought a remarkable advantage in comparison to other co specifics, to rivalling animals or to the quarry.
The findings of Makapan
Osseous findings at a limestone cave located in Makapan, South-Africa, led to the question to what extent this advantage, in combination with a more and more improved skill using tools, affected the behavior of the apes.
These findings showed explicit cracks and fractures, which are likely to be done on purpose. Additionally, there were clubs, bludgeons and spears formed by the long limb bones or the horns of antelopes. This new special weapon leaves small punctured, round and triangular holes in skulls, depending on how it was formed.
This new development in building weapons shows a clear increase concerning the aggression of the animals.
Dart carries that issue to extremes and equips this new type of ‘carnivorous and killing’ apes (“proto-men” in his own words) with weapons. Furthermore he describes them as organized in a tribe, so they were able to hunt bigger animals. The ability of making fire and remarkable social skills prompt Dart to bring them more in line with humans.
Observations from Sgt. H. B. Potter (Zululand, South Africa) show, that this kind of development is still up to date as it is mentioned in “The predatory transition from ape to man” by Raymond Dart. He describes a pride of baboons that hunts antelopes. Indeed, he admits that this depends on seasonal circumstances, because nutrition was rare. Nevertheless, he proves explicit behavior.
The eating habits
Concerning the eating habits from then until now, Dart argues that there has always been an ambition to eating meat: grubs and insects, bigger mammals and even human flesh (i.e. distinctive cannibalism) are the results.
A so called deficit from “animal proteins” has to be compensated, so consuming meat is essential to survive.
The comment written by the editor of Dart’s article Dr. Alan H. Kelso shows how few scientists accepted the new ideas of Dart and Ardrey. Not only did Dart require a long time to publish his work, but also the epilogue contains notices like: “Professor Dart’s thesis that the South African apemen, at the stage they were found, were omnivorous, must be considered as proven. Of course, they were only the ancestors of the modern Bushmen and Negroes, and of nobody else.”
Another obvious evidence would be the rejection of Dart’s thesis by a scientific convention at Livingstone (Zambia, South-Africa), what led Ardrey into writing his book “African Genesis”. He felt himself forced to defend the opinion of his mentor.
Just as well, the ethologist Konrad Lorenz showed interest before and brought out his book “On Aggression” (1963). In his introduction he describes rivalling butterfly fish, which defend their territory that leads over to the question, if humans, too, tend to intraspecific behavior.
The "Declaration of Seville", released under US auspices in 1986, stated that while patterns of human aggression may be inherited, warfare need not be a necessary consequence.
References in fiction
This theory can be seen in the opening sequence of 2001: A Space Odyssey, and also appears in the television show Sliders, which made extensive use of the killer ape theory in arcs involving the Kromaggs.