Deep beneath the dust of the Cradle of Humankind, in the rolling hills northwest of Johannesburg, South Africa, archaeologists discovered a treasure trove of insights into the lives of our human ancestors.
Now, unusual skull fragments and a constellation of fossil clues challenge the very core of the story of our human ancestors.
These new discoveries reveal one trait divided which species survived, and which died out: adaptability.
In this fossil trove, scientists discovered a skullcap belonging to a toddler Homo erectus.
The specimen, which researchers have named DNH 134, is the first Homo erectus fossil found in South Africa ever. It is also the earliest example of Homo erectus discovered to date. It offers solid proof that our direct human ancestor is some 150,000 to 200,000 years older than scientists thought.
Previously, the oldest Homo erectus in the world was found in Dmanisi, in Georgia, dating to 1.8 million years ago, the researchers explain. This two-year-old's skull shows they were around as many as two million years ago.
“Homo erectus was perhaps the first species we would look at and recognize as being more human-like,” Andy Herries, coauthor on the new study and paleoanthropologist at La Trobe University in Australia, tells Inverse.
Homo erectus were perhaps the first true trailblazers of the hominin family. They were the first human species to leave the African continent, and they extended their range all the way to Asia, Herries explains.
“This is ultimately the beginning of the story of us, as the great generalists, able to live in all different environments on Earth."
Amazingly, the team also found the earliest known Paranthropus robustus skull fragment too, which they named DNH 152.
The parallel discoveries reveal that three species of hominins, Homo erectus, Parathropus, and Australopithecus africansis, lived in the South African highlands simultaneously.
Herries and his team published their findings Thursday in the journal Science.
The life and times of Homo erectus
The Homo erectus skull fragments were discovered in the Drimolen Main Quarry, a notoriously challenging place to excavate, Herries says. The fossil-containing rocks there can be "as hard as concrete,” he says.
Dating the fossils once they are recovered is also a difficult process.
By using a combination of novel technologies and by comparing the skulls to other fossil fragments of lizards, bats, and soil samples, the team reconstructed a timeline of the young Homo erectus’ life and death.
The two skull fossils, DNH 134 and DNH 152, reveal that not only did they all live together, but Homo erectus, Paranthropus, and Australopithecus all possessed distinct traits that speak to their place in the human family tree.
For example, Australopithecus was more ape-like than human-like, and experienced serious “dietary stress” compared to their other hominin cousins, Herries says.
When the two other hominin species came on the scene, they developed flexible, new ways of operating that may have given them an evolutionary edge.
“Our work is a reminder that once upon a time we shared this world with other human species and that we are now the last remaining one."
"Paranthropus robustus and Homo erectus arrived on the South African landscape with completely different ways of adapting to the world around them, and new technology in the form of stone and bone tools,” Herries says.
Paranthropus robustus were shorter than Homo erectus and Australopithecus, and possessed larger teeth. That trait enabled them to eat tough, hard plants, like roots and tubers.
Homo erectus, by comaprison, were taller and more slender than their peers, and ate easier to digest foods, like fruits and berries.
Ultimately, Paranthropus robustus and Homo erectus replaced Australopithecus. Part of what enabled Paranthropus robustus in particular to survive is the fact that these hominins were "specialists," Herries says. But ultimately, that same specialism may have caused their extinction.
Adaptability is the key
Unlike the other two hominins, Homo erectus' great advantage was their sheer adaptability. They could travel long distances, a crucial ability that enabled them to adjust to a rapidly changing environment.
In fact, their wandering nature is part of why Homo erectus proved to be the most successful species of ancient humans ever known, Susan Antón, an anthropologist at New York University who wasn’t involved in the study, asserts in a related commentary published in the journal Science.
The species endured for more than a million years, before going extinct half a million years ago. Their last-known residence was in present-day Java.
Homo erectus was also able to acclimatize to a changing Earth better than its fellow hominins. aranthropus and Australopithecus evolved in warm and humid climates but then the weather began to shift from warm and humid, to cool and dry. Homo erectus thrived in the cooler climate, while the other two hominins struggled to adapt.
As the climate cooled, tree-cover in the South African highlands declined, and grasses took their place. Eventually the forests were replaced with the African savannah grasslands of today.
Homo erectus were the only species among the three to endure these changes.
Homo erectus may have lived some two million years ago, but these incredible ancient humans offer lessons for humans today.
After all, we too now find ourselves in a state of environmental and social flux.
“Our work is a reminder that once upon a time we shared this world with other human species and that we are now the last remaining one,” Herries says.
“We should not be so foolish as to think that we cannot suffer the same fate as our early humans cousins, who ultimately went extinct because they were unable to adapt and innovate to challenges in their changing world.”
Homo erectus invented novel technologies, adjusted to their changing landscape, and survived longer than other hominins — all important lessons modern-day Homo sapiens may draw from.
Ultimately, the pair of discoveries shed light on a critical period of time in the human story. These first steps are what has led to our globalized world today, Herries says.
“It is also a reminder in these unconnected times, with border closures and an increasing fear of other people and groups, that we are ultimately one family, all connected by a common origin in Africa," Herries says.
"We should be working together to fight the challenges of the future, both in terms of pandemics and climate change."
Understanding the extinction of Australopithecus and origins of Paranthropus and Homo in South Africa has been hampered by the perceived complex geological context of hominin fossils, poor chronological resolution, and a lack of well-preserved early Homo specimens. We describe, date, and contextualize the discovery of two hominin crania from Drimolen Main Quarry in South Africa. At ~2.04 million to 1.95 million years old, DNH 152 represents the earliest definitive occurrence of Paranthropus robustus, and DNH 134 represents the earliest occurrence of a cranium with clear affinities to Homo erectus. These crania also show that Homo, Paranthropus, and Australopithecus were contemporaneous at ~2 million years ago. This high taxonomic diversity is also reflected in non-hominin species and provides evidence of endemic evolution and dispersal during a period of climatic variability.