The Killer Ape Theory: Are Humans Violent by Nature?

This article is an excerpt from the Shortform book guide to "Humankind" by Rutger Bregman. Shortform has the world's best summaries and analyses of books you should be reading.

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What is the Killer Ape Theory? Are humans violent by nature?

According to the Killer Ape Theory, aggression and violence are what propelled human evolution, distinguishing our ancestors from other primates. The theory gained notoriety for suggesting that humans were aggressive by nature. However, not all scientists are unanimous in this opinion. According to Rutger Bregman, the author of Humankind, more recent evidence suggests that human nature is peaceful and cooperative.

Here’s why the Killer Ape Theory is moot, according to Bregman.

Early Human Foragers Avoided War

According to Bregman, early human foraging groups lived peacefully with each other for millions of years. These groups struggled to survive in the face of harsh weather conditions and predators, but evidence suggests that they didn’t go to war against each other. 

When scientists first discovered the bones of early humans, they theorized that our ancestors were brutal killers and cannibals. In the 1920s, anatomist Raymond Dart studied the skull of an Australopithecus africanus, a human ancestor that lived 2 to 3 million years ago. Based on the skull’s injuries, Dart concluded that these early humans violently murdered one another. He published his theory in the 1950s, calling it “Killer Ape Theory.”

(Shortform note: While Bregman focuses on the development of Killer Ape Theory, Dart’s study of the skeletal remains of Australopithecus africanus also resulted in another important finding: that humans originated in Africa. Charles Darwin had proposed that Africa was the birthplace of humanity in his 1871 book The Descent of Man. But by the 1920s, most theories suggested that the first humans lived in Eurasia, based on skeletal remains found in France and England. Dart suggested that Australopithecus africanus, discovered in South Africa, predated these remains. While his theory was dismissed at the time, later findings confirmed that he was right.)

However, Bregman notes that more recent studies have debunked Killer Ape Theory and revealed that our ancestors were peaceful. In 2006, archaeologists examined the same Australopithecus africanus skull that Dart had studied in the 1920s. They found that the injuries came from a large predatory bird, not from other early humans. Skeletal remains from later in history tell a similar story: According to Bregman, not a single archaeological site suggests that early human foragers fought against each other

(Shortform note: Bregman argues that the archaeological record doesn’t show evidence of war in foraging societies. However, other authors point out that this doesn’t necessarily mean that war didn’t happen. In a podcast episode featuring Bregman and renowned psychologist Steven Pinker, Pinker argues that some war injuries from prehistoric times—such as cuts and bruises—wouldn’t show up on skeletons. As a result, it’s difficult to draw firm conclusions about the prevalence of war from early human remains.)

Scientists Have Objected to Killer Ape Theory for Decades

Bregman implies that Killer Ape Theory wasn’t debunked until relatively recently. However, paleontologists have questioned and debunked Dart’s theory since its incipience in 1953. 

The most prominent among these early critics were C.K. Brain and Elizabeth S. Vrba, whose 1970 study suggested that the injuries to the Australopithecus africanus skull came from leopards, not from other early humans. The researchers noted that two puncture marks in the eye cavities of the skull were exactly the same distance apart as an adult leopard’s teeth. They theorized that the leopard dragged the owner of the skull into a tree—the skull then fell, causing the damage that Dart attributed to an early human bashing the skull with a rock.

While the 2006 study that Bregman cites agreed that a predator, not another early human, caused the damage to the skull, the researchers interpreted the puncture marks differently. They observed that the puncture marks matched those on the skulls of monkeys that had been killed by large eagles. They therefore suggested that the Australopithecus africanus was the victim of an eagle, not a leopard.

The Killer Ape Theory: Are Humans Violent by Nature?

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  • Why humans are fundamentally good, not evil
  • How the Stanford Prison Experiment was misleading
  • How recent studies have debunked "Killer Ape Theory"

Darya Sinusoid

Darya’s love for reading started with fantasy novels (The LOTR trilogy is still her all-time-favorite). Growing up, however, she found herself transitioning to non-fiction, psychological, and self-help books. She has a degree in Psychology and a deep passion for the subject. She likes reading research-informed books that distill the workings of the human brain/mind/consciousness and thinking of ways to apply the insights to her own life. Some of her favorites include Thinking, Fast and Slow, How We Decide, and The Wisdom of the Enneagram.

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