October 17, 2011
If you know anything about human evolution, it’s probably that humans arose in Africa. But you may not know how scientists came to that conclusion. It’s one of my favorite stories in the history of paleoanthropology—one that involves an anatomist you’ve probably never heard of and an infant who was attacked by an eagle and dropped into a hole almost three million years ago.
The idea that humans evolved in Africa can be traced to Charles Darwin. In his 1871 book The Descent of Man, Darwin speculated that it was “probable” that Africa was the cradle of humans because our two closest living relatives—chimpanzees and gorillas—live there. However, he also noted, a large, extinct ape once lived in Europe millions of years ago, leaving plenty of time for our earliest ancestors to migrate to Africa. So, he concluded, “it’s useless to speculate on the subject.”
By the early 20th century, the world’s leading anatomists thought they knew the answer: Humans evolved somewhere in Europe or Asia. By then, Neanderthals had been found in Europe; Java Man (now known as Homo erectus) had been discovered in Indonesia and Piltdown Man (later exposed as a hoax) had been unearthed in England. Although these ancient beings were primitive, they clearly resembled modern humans.
In 1924, a fossil discovery in South Africa challenged this view of a Eurasian homeland and revolutionized the study of human evolution.
Raymond Dart, an Australian-born anatomist working at the University of Witwatersrand in Johannesburg, was interested in fossils. In the fall of 1924, as Dart was preparing to attend a wedding, two boxes of rocks blasted from a limestone quarry near the town of Taung were delivered at his house. Over the objections of his wife, Dart, dressed in formal wear, dug into one of the boxes. He found something amazing: the fossilized mold of a brain.
This was a special brain. The shape and folds on the brain’s surface implied it belonged to some kind of human—perhaps an ancient human ancestor, Dart thought. Further digging led Dart to another rock that the brain fit perfectly into. After months of careful chipping, Dart freed the brain’s corresponding face and lower jaw on December 23. “I doubt if there was any parent prouder of his offspring,” Dart later wrote in his 1959 book Adventures with the Missing Link, “on that Christmas of 1924.”
It was probably the best Christmas present a paleoanthropologist could ever receive. The creature’s baby teeth revealed that it was a child (probably 3 or 4 years old, scientists now think). Other features of the so-called Taung Child confirmed Dart’s suspicion that he was handling a human ancestor. Although the being looked apish in many ways, the face lacked a pronounced muzzle as seen in chimps and gorillas. And the placement of the hole through which the spinal cord exits the bottom of the skull—the foramen magnum—suggested the Taung Child had an erect posture and walked upright on two legs (animals that travel on four legs, such as chimps and gorillas, have a foramen magnum more toward the back of the skull).
Dart wasted no time in reporting his results, announcing in early February 1925, in the journal Nature (PDF), that he had found “an extinct race of apes intermediate between living anthropoids [monkeys and apes] and man.” He named it Australopithecus africanus (“Southern Ape of Africa”).
Australopithecus africanus did not receive a warm welcome from experts in the field. In the minds of most academics, there was a lot to criticize. Many derided Dart for rushing to publication, and media hoopla surrounding the announcement—before experts had a chance to take a close look at the finding—irked more established anatomists. Researchers even ridiculed Dart for mixing Latin and Greek when inventing the name “Australopithecus.”
The biggest problems were scientific. No one had any idea what the Taung Child would have looked like as an adult. Furthermore, in addition to being from the wrong continent, the fossil was too ape-like to fit the early-20th-century view of human evolution. At the time, fossils like Piltdown Man indicated the earliest humans evolved big brains before other aspects of modern human physiology emerged—even before the ability to walk upright. Thus, experts dismissed the Taung fossil as just an old ape.
But at least one person thought Dart was right. Paleontologist Robert Broom took up Dart’s cause. While investigating several limestone caves in South Africa during the 1930s and 1940s, Broom discovered numerous fossils of adult “ape-men” specimens that looked similar to Dart’s Taung Child. The mounting evidence—plus the uncovering of the Piltdown Hoax in the late 1940s and early 1950s—convinced even the most ardent skeptics that australopithecines belonged in the human family, and that Africa was the birthplace of humans. The work dramatically altered the trajectory of human evolution studies, changing where people looked for human fossils and what they expected to find.
Not all of Dart’s ideas have stood the test of time, however. As fossils of australopithecines were uncovered in South African caves, Dart noticed they were always found in association with animal parts—particularly the teeth, jaws and horns of hoofed animals. Dart believed these were the remains of an “osteodontokeratic” (bone, tooth and horn) culture, in which early humans used these broken bits as tools for warfare and hunting. Scientists later realized that predators such as leopards had accumulated the heaps of bones. In fact, holes on the Taung Child reveal it was the victim of a hungry eagle that dropped part of its meal into the entrance of the cave where the fossil was eventually found.
I never get tired of the story of Raymond Dart, in part because the Taung Child is kind of an adorable fossil. But mostly it’s because Dart’s work is a great reminder that nothing in human evolution is written in stone; you have to keep an open mind.
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