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How Australopithecus provided insight into human evolution

In 1925, a Nature paper reported an African fossil of a previously unknown genus called Australopithecus. This finding revolutionized ideas about early human evolution after human ancestors and apes split on the evolutionary tree.
Dean Falk is in the Department of Anthropology, Florida State University, Tallahassee, Florida 32310, USA, and is also at the School for Advanced Research, Santa Fe, New Mexico.
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Raymond Dart and the Taung skull, February 1925.

Figure 1 | Raymond Dart in 1925 holding the Australopithecus africanus fossil called the Taung Child.Credit: School of Anatomical Sciences/WITS

Australian-born Raymond Dart had barely started his job as chair of the anatomy department of the University of the Witwatersrand in Johannesburg, South Africa, when he made a momentous discovery. Using his wife’s knitting needles, he painstakingly extracted a fossil (Fig. 1) from a chunk of rock found in Taungs (now known as Taung), South Africa. As he recalled1, “the rock parted … What emerged was a baby’s face, an infant with a full set of milk teeth … I doubt if there was any parent prouder of his offspring than I was of my ‘Taungs baby’ on that Christmas of 1924.” Better yet, the fossil fitted neatly with another type of fossil, called an endocast, formed from sediments accumulated inside the skull. The endocast reflects brain-surface details stamped on the braincase’s inner walls. These fossils revealed a combination of ape-like and human-like features never previously reported together.

Convinced that the specimen, called the Taung Child, represented an extinct link between humans and our ape ancestors, Dart dispatched a report2 to Nature by mail boat. He probably felt some trepidation because several fellows of the Royal Society in London, who had mentored and taught with him, considered the human forerunner to be the British specimen known as Piltdown Man (which was later exposed as a hoax). Piltdown Man’s human-sized brain and ape-like jaw contrasted with the Taung Child’s ape-sized brain and human-like jaw and teeth. In Dart’s view, the Taung Child looked more primitive and older than the main existing candidates for the earliest ancestral human relative — Piltdown Man and Java Man (Homo erectus) from Indonesia. Dart therefore described the Taung Child as a ‘man-ape’ rather than an ‘ape-man’, like Java Man, and named the species Australopithecus africanus, which means southern ape from Africa.

Dart declared that humankind’s cradle was not in Indonesia or Britain as his contemporaries thought, but was instead in Africa, as Charles Darwin had previously suggested3. The comfortable habitats favoured by African chimpanzees and gorillas in Dart’s time were more than 3,200 kilometres north of where the Taung Child dwelled, and Dart suggested in his 1925 Nature paper that intense competition for limited resources in harsh southern African landscapes “furnished a laboratory such as was essential to this penultimate phase of human evolution”. In the paper, he also reasoned that “enhanced cerebral powers possessed by this group … made their existence possible in this untoward environment”, attributing intelligence based on his interpretation of human-like brain convolutions at the back of the specimen’s endocast.

When the paper appeared, the Taung Child and 32-year-old Dart became world famous overnight. Yet not everyone was receptive to new ideas about human evolution. Indeed, five months later, a court case known as the Scopes monkey trial began in the United States to settle whether evolution could be taught in Tennessee schools. The immediate reaction to Dart’s paper was mainly enthusiastic, but he soon became a target of ‘you’ll-burn-in-hell’ letters from religious fundamentalists, and his former London colleagues published harsh criticisms of his research. Dart’s main champion, the physician Robert Broom, remarked4: “It makes one rub one’s eyes. Here was a man who had made one of the greatest discoveries in the world’s history — a discovery that may yet rank in importance with Darwin’s Origin of Species; and English culture treats him as if he had been a naughty schoolboy.”

To answer his critics, Dart spent four years preparing a book5 about the Taung Child. It provided voluminous extra details about the endocast, bones and teeth, and bolstered the argument that humans originated in Africa6. He submitted the book to the Royal Society, which declined to publish it. The pro-Piltdown fellows were probably behind this rejection7. Sadly, the book remains unpublished.

The most controversial aspect of Dart’s paper, then and now, is his view that the back of the Taung Child’s endocast is human-like. Some have argued that Dart misidentified a skull imprint as a brain groove similar to a human one, a feature that is inconsistent with the Taung Child’s otherwise ape-like brain8. Dart’s 1925 Nature paper describes two endocast brain grooves, but his book identifies 14 further grooves, and describes 3 dispersed brain regions that look expanded in comparison with those of ape brains. If these findings had been published, they might have influenced the still-controversial debate about whether the human brain evolved in a piecemeal, mosaic fashion or in a more globally connected manner. Some mosaicists still cite Dart’s 1925 Nature paper, but his unpublished book reveals his globalist viewpoint.

Dart’s paper stated: “we may confidently anticipate many complementary discoveries concerning this period in our evolution.” Indeed, thousands of specimens have been found that represent various Australopithecus species that lived in Africa during different time spans from more than 4 million to around 1 million years ago. The fossil Lucy is an example of one such species, called Australopithecus afarensis.

Subsequent work confirmed that Dart got most of the details right regarding his discovery. Australopithecus shared features of both living apes and humans, and they were bipedal as he surmised because the skull opening that accommodates the spinal cord is positioned centrally at the base of the specimen’s cranium. Dart correctly inferred9 that hominins originated in Africa, and that our genus Homo arose from Australopithecus. Happily, he lived long enough to see his initially iconoclastic ideas become widely accepted.

I cannot help but wonder what Dart would have thought about another notable discovery reported in Nature10 — the 2004 identification of a species called Homo floresiensis (the most complete specimen is nicknamed the Hobbit) from remains in Indonesia dating to approximately 100,000–60,000 years ago. Like the Taung Child, the H. floresiensis specimens showed a combination of features never previously found in a fossil specimen. Homo floresiensis had ape-like, Australopithecus-like and human-like traits, as well as a tiny brain, leading some to suggest that this species might be a lineage descended from a previously unknown early hominin migration out of Africa11.

The parallels with Dart’s discovery are remarkable. Homo floresiensis drew worldwide attention, but was also met with scorn from some scientists (who argued that the Hobbit represents an abnormal human). Homo floresiensis-like fossils dating to 700,000 years ago have since been reported12, and its legitimacy as a species is gaining traction. It might be equally crucial for unravelling the evolution of early members of the human family tree outside Africa in the way that the Taung Child was essential for understanding the evolution of human ancestors in Africa. Only time will tell. One thing is certain, however; the more palaeoanthropology changes, the more palaeopolitics stays the same.

Nature 575, 41-42 (2019)

References

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    Dart, R. A., with Craig, D. in Adventures with the Missing Link 10 (Harper, 1959).

  2. 2.

    Dart, R. A. Nature 115, 195–199 (1925).

  3. 3.

    Darwin, C. The Descent of Man, and Selection in Relation to Sex (Appleton, 1871).

  4. 4.

    Broom, R. in Finding The Missing Link 27 (Watts, 1950).

  5. 5.

    Dart, R. A. Australopithecus africanus: And His Place in Human Origins (unpublished manuscript, Univ. Witwatersrand Archives, 1929).

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    Falk, D. Am. J. Phys. Anthropol. 140 (Suppl. S49), 49–65 (2009).

  7. 7.

    Falk, D. The Fossil Chronicles: How Two Controversial Discoveries Changed Our View of Human Evolution (Univ. California Press, 2011).

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    Keith, A. in New Discoveries Relating to the Antiquity of Man 84–85 (Norton, 1931).

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    Dart, R. A. J. Hum. Evol. 2, 417–427 (1973).

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    Brown, P. et al. Nature 431, 1055–1061 (2004).

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    Argue, D., Groves, C. P., Lee, M. S. Y. & Jungers, W. L. J. Hum. Evol. 107, 107–133 (2017).

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    van den Bergh, G. D. et al. Nature 534, 245–248 (2016).

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