Celebrating a Century of Human Fossils from Africa
Around 10 a.m. on June 17, 1921, a young boy sunk his pickaxe into a crumbling cave wall in the Broken Hill mine near the village of Kabwe in Zambia, Africa. Looking on was Tom Zwigelaar, a Swiss miner employed by the Rhodesia Broken Hill Development Company. The two were searching for lead and zinc. But that day, one hundred years ago today, they found an ancient skull.
It was the very first fossil of an ancient human ancestor ever discovered on the African continent.
Zwigelaar would later report to anthropologist Aleš Hrdlička that he first mistook the fossil for the skull of a gorilla. He never did recount the name of the “colored boy” who helped unearth it. The Broken Hill skull eventually made its way to London where it was studied by paleontologist Sir Arthur Smith Woodward who declared in the pages of Nature only five months later that it represented a form he thought was intermediate between Neandertals and modern humans. He called it Homo rhodesiensis.
Human fossils had been known for some time. In 1864, William King proposed that a partial skeleton found in a cave in the Neander valley, Germany belonged to an extinct species he called Homo neanderthalensis. In 1891, Javanese men forced to dig trenches along the Solo River by the colonial government delivered a small skull to Dutch anatomist Eugène Dubois, who named it Pithecanthropus erectus. Today, this roughly 1 million-year-old fossil from Indonesia is attributed to Homo erectus. Woodward himself was no stranger to human remains. In 1913, he declared that fragmentary bones plucked from a quarry near Piltdown village in Sussex, England represented an ancient human he called Eoanthropus dawsoni. Many of his colleagues were skeptical and by the middle part of the 20th century, the Piltdown fossils were exposed as an elaborate and well-planned hoax.
But what was found in the depths of the Broken Hill mine was different from these others. It was African.
A half century earlier, Charles Darwin hypothesized in The Descent of Man (1871) that the birthplace of the human lineage was likely to be Africa. He wrote,
In each great region of the world the living mammals are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man’s nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.
It was solid reasoning and prophetically written despite the almost complete absence of a fossil record or knowledge of molecular genetics. But was he right? The answer is a resounding “yes” and it all began with the skull from the Broken Hill mine.
Today, literally thousands of fossils of our ancient ancestors are curated in Museums throughout the African continent. The largest cache of nearly 2000 fossils from 18 different individuals was discovered deep within the Rising Star Cave, South Africa in 2013 and declared a new species, Homo naledi. Occasionally researchers discover partial skeletons such as “Lucy”, a 3.18-million-year-old Australopithecus afarensis discovered in Ethiopia in 1974, or the “Nariokotome Boy”, a 1.49-million-year-old Homo erectus found in Kenya in 1985. But most fossils are isolated teeth, jaws, fragmentary limbs, ribs, fingers and toes. These fossils are all that is left of once living, breathing, thinking beings who laughed, cried, lived, and died. We’ve discovered fossils of individuals who, in life, had painful arthritis, healed bone breaks, or cancer. From their bones, we have learned what many of our ancestors and extinct relatives ate, how they gave birth, when they weaned their babies, how they grew, how they moved, and even how many of them died. Every one of these fossils has a story to tell, and every fossil deserves to have its story told. As a paleoanthropologist, a scientist who studies the fossilized remains of our ancestors, I am fortunate to have the opportunity to interpret these bones and share with the world what they tell us — about us.
So, what have we learned in a century’s worth of work? We now know that the branch of the ape family tree that eventually evolved into humans had fully split from the ancestors of chimpanzees and bonobos by six million years ago. Fossils close to this age have been pulled from ancient sediments in Chad, Kenya, and Ethiopia and they reveal ape-like ancestors with relatively small brains who could skillfully climb through the trees. But when they descended to the ground, they did not knuckle-walk; they moved on two legs. Of all the ways we differ from our ape cousins, it was walking on two legs — a locomotion called bipedalism — that launched the great human experiment.
For millions of years, our upright walking ancestors and extinct relatives diversified into different populations and species found in varying habitats across the vast stretches of land east from modern day Chad to Ethiopia and south to South Africa. By three million years ago, our clever predecessors had invented rudimentary stone tools. Fossil skulls just a million years younger document the beginnings of brain expansion in the earliest members of own genus, Homo.
Homo sapiens is an evolutionary newcomer. The three oldest fossil skulls discovered from our own species have been found in Morocco, South Africa, and Ethiopia — the geographic corners of the enormous triangular shaped African continent. They, and other fossils, show that the pan-African evolution of our species happened gradually from 260,000 to 350,000 years ago. But there is more to us than our anatomy. In caves scattered along the coastline of South Africa, researchers have discovered the oldest jewelry, evidence for body adornment, carvings, and drawings. Just this year, paleoanthropologists working in Kenya carefully documented the oldest deliberate burial: a child, gently laid into the earth 78,000 years ago.
Fossil discoveries help us answer some scientific questions, but they inevitably lead to new ones we never even thought to ask. Thus, science marches on. While we have learned so much about our origins and evolution in the 100 years since the Broken Hill skull was found, we have more questions than ever. The pace of discovery has accelerated thanks to advances in technology, data sharing and scientific collaboration, the extraction of ancient DNA and proteins from fossils, important steps toward decolonizing our discipline, and — perhaps most of all — the straightforward curiosity of earnest students all over the world.
And what of the Broken Hill skull? Negotiations are underway for the skull to be returned to Zambia. Just last year, researchers performed a detailed chemical analysis of the skull and calculated that this individual died about 300,000 years ago, a surprisingly young age that overlaps with the very first Homo sapiens. Our species shared the African landscape with another kind of human. Did we fill different niches, or did we compete for resources? Was there hostility? Did we interbreed with them? These questions and many, many more await answers as paleoanthropologists embark on a second century of searching for fossils on the continent from which we humans sprung.
Jeremy DeSilva is an associate professor of Anthropology at Dartmouth College. He is the author of First Steps: How Upright Walking Made Us Human (HarperCollins, 2021) and the editor of A Most Interesting Problem: What Darwin’s Descent of Man Got Right and Wrong about Human Evolution (Princeton University Press, 2021).
