The human story begins in Africa. Of the many fascinating fossil sites in Africa, an important one is the Cradle of Humankind outside of Johannesburg, South Africa. The many caves and rock outcrops of this UNESCO world heritage site, and just outside of it, have produced fossils of up to five hominin species, including Australopithecus africanus , Paranthropus robustus , Homo habilis , Homo erectus , and Homo naledi . This makes the Cradle of Humankind a chronicle of human evolution, covering about 3 million years from the rise of Australopithecus africanus to almost the present.
Famous human evolution scientist Lee Berger holds the skull of Homo naledi, which was found in 2015 in the Cradle of Humankind area of South Africa. ( Wits University )
The South African Network Sites in the Cradle of Humankind
The site or network of sites dubbed the “Cradle of Humankind” is located in the Rocky Highveld Grassland of South Africa . The Highveld Grassland, or the Highveld, is classified as a “fire climax grassland.” This means that wildfires play an important role in the local ecosystem, including the balance between grass and trees. The grasslands also have a large temperature range over the course of the year, from -12 degrees Celsius (10 degrees Fahrenheit) to 39 degrees Celsius (102 degrees Fahrenheit).
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The animals in the modern Highveld include antelope, many bird species, hyenas, leopards, owls, bats, and rodents. The cave systems within the Highveld is used for roosting by bats and owls. The owls will sometimes bring rodent remains into the caves. This is important for paleoenvironmental reconstruction. Over the course of the past 3 million years, the region has been inhabited by lions, baboons, hyenas, saber-toothed cats, and, of course, hominins.
Over the past century and a half, irresponsible use of the land has led to significant environmental degradation through overgrazing, waste dumping, and contamination of water by agrochemicals. Nonetheless, industry in the area has led to the discovery of a wealth of fossils which tell the story of human evolution in southern Africa.
Replica crania of (left to right) Homo habilis (KNM-ER 1813, Koobi Fora, Kenya ∼1.8 million years old), an early Homo erectus (D2700, Dmanisi, Georgia ∼1.8 million years old) and Homo floresiensis (Liang Bua 1, Indonesia ∼20,000 years old) are compared with actual fragments of cranial material of Homo naledi that have been overlaid on a virtual reconstruction (far right; note some of the images of H. naledi material have been reversed). (Chris Stringer / CC BY 4.0 )
Hominins of the Cradle of Humankind
Today, there is one species of hominin in the Highveld, Homo sapiens . For millions of years, however, the landscape was much more diverse. For millions of years, multiple hominin species appear to have coexisted in the Cradle of Humankind. At one point, perhaps 2 million years ago, there were as many as three different genera of hominins in the area simultaneously, australopithecines (genus Australopithecus), paranthropines (genus Paranthropus), and humans (genus Homo). Some major hominin species that dominated the area include Australopithecus africanus , Paranthropus robustus , Homo erectus , and Homo naledi .
The original complete skull (without upper teeth and mandible) of a 2.1-million-year-old Australopithecus africanus specimen known as “Mrs. Ples.” (José Braga; Didier Descouens / CC BY-SA 4.0 )
The first specimen of A. africanus was found at the Taung site of the Cradle of Humankind in 1924 and described by Raymond Dart. Dart believed that this new species represented a human ancestor, but this was originally rejected on account of its small brain. Over time, however, more evidence from later discovered fossils was gathered which demonstrated that A. africanus was related to the ancestors of the genus Homo.
A. africanus flourished as a species between 3.3 Ma (Million years ago) and about 2.1 Ma. It was bipedal, as shown by its femur, foot bones, and pelvis. Nonetheless, it appears to have still had tree climbing abilities based on its shoulders and hand bones. A. africanus had a rounder skull and smaller teeth than modern non-human great apes, but it still had an ape-like jutting face. It also had relatively long forelimbs which also would have given it a more ape-like appearance.
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The original specimen of A. africanus was found near bone fragments which Dart originally interpreted to be bone tools used by A. africanus as hunting weapons. It is now believed that these bone fragments were the work of lions, hyenas, and leopards which also ate A. africanus on occasion. It is now believed by paleoanthropologists that the diet of A. africanus was not that different from modern chimpanzees, consisting mainly of fruit, nuts, plants, and insects.
Overall, A. africanus reflects the beginning of the more human-like great apes with its bipedalism, rounder skull, and smaller teeth. Nonetheless, it was still very ape-like and did not signal the beginning of physically recognizable humanity.
DNH 7, the most complete skull of Paranthropus robustus, a female, ever discovered from Drimolen Main Quarry, photographed at the University of the Witwatersrand, South Africa. (DrHerries / CC BY-SA 4.0 )
In 1938, a fossil jaw was found in Kromdraai, South Africa by a schoolboy by the name of Gert Terblanche. It was later examined by scientists, including Robert Broom. Broom realized that the jaw must have been from a completely different type of hominin than the previously discovered australopithecines. This was due to its thickness and the large molars rooted in it. Originally called Australopithecus robustus , enough evidence has been gathered that the hominin is now considered to be in a separate genus, Paranthropus. P. robustus flourished between about 1.8 Ma and 1.2 Ma.
P. robustus was different from the australopithecines in that it had very large teeth and a large sagittal crest atop the skull. This may have given it a more gorilla-like appearance compared to the chimpanzee-like A. africanus . The large cheek teeth were probably for processing fibrous foods. The sagittal crest was probably an anchor point for the powerful muscles that it would have needed for chewing. P. robustus also had a wide, dish-shaped face which likely reflected anatomical adaptations for its diet. Although P. Robustus likely ate roots, tubers, seeds, and other hard foods, paleoanthropologists believe it may also have eaten softer foods such as fruit and leaves.
Currently, no stone tools have been found in association with P. robustus , although there is evidence that it may have used bones as tools to exploit termite mounts in the manner of some modern great apes. This would be evidenced by the ends of the tools being rounded and polished from repeated use.
P. robustus demonstrates how similar species can evolve in very divergent ways based on how they adapt to their environment. The direct ancestors of modern humans, whatever they may have been, likely adapted to their surroundings through the evolution of the greater intelligence needed to work with increasingly complex tools. This probably led to the human “look” compared to other great apes. This would include a rounder skull and smaller teeth to accommodate a larger brain. The paranthropines, on the other hand, went in a very different direction. Instead of adapting to their environment through increasing tool use, requiring gradual growth of the brain at the expense of other features, it appears that they adapted to their environment through evolving powerful jaws and large teeth for a specialized diet. Thus, P. robustus shows that human evolution could have gone in a very different direction and produced a rather different kind of animal.
Homo habilis, depicted in this illustration, is one of the earliest members of the genus Homo. (López Caamaño, et al / Xunta de Galicia )
This species is one of the earliest members of the genus Homo. It lived from about 2.4 Ma to about 1.4 Ma and coexisted with its eventual ecological successor, Homo erectus , for half a million years. Homo habilis had a larger brain than the australopithecines, but it still had a more ape-like body with relatively long forelimbs and a slightly jutting face. The name of Homo habilis means “handy man” since it was originally believed to be the first toolmaker. Until recently, the earliest stone tools dated to 2.6 Ma which is slightly before the first examples of H. habilis appear in the fossil record (⁓2.4 Ma). It is now known that the oldest stone tools date to about 3.3 Ma, making it even more likely that the earliest toolmakers were australopithecines. Homo habilis does not make as prominent of an appearance as its hominin cousins in the Cradle of Humankind. Nonetheless, there are bones at the Sterkfontein site that have been attributed to H. habilis .
Skeleton and a life reconstruction of the Homo erectus youth known as Turkana Boy. (Mauricio Antón / CC BY 4.0 )
The first specimen of the species now called Homo erectus was found in Indonesia in 1891. H. erectus is the earliest known human species to have had a modern human-like body with relatively long hind-limbs (i.e., legs) and shorter forelimbs (i.e., arms). This implies that it no longer had adaptations for tree climbing.
H. erectus were the first humans to live more like us than chimpanzees or gorillas. They were more innovative with stone tools than their predecessors. The tools developed by H. erectus are collectively referred to as the Acheulean toolkit or industry. This toolkit consisted of large cutting tools, such as the stone age hand axe and cleaver. It is possible that a more diverse set of tools is what allowed H. erectus to survive as long as they did, despite climate changes and competition with other hominin species. Large brains and tall bodies would also have required higher protein content in their diet, suggesting that meat was an important part of the diet of Homo erectus. This suggests that H. erectus probably hunted or at least scavenged for meat.
H. erectus was probably the first human species to “leave Africa” and lasted for almost 2 million years from 1.9 Ma to ⁓110,000 years B.P. (Before Present). One of the last regions inhabited by H. erectus was Indonesia where they may have coexisted with several other hominin species including Homo floresiensis and Homo sapiens .
Like H. habilis , H. erectus did not originate in South Africa, but they did have a presence there for over a million years. It is not entirely clear what caused H. erectus to migrate to South Africa. One possibility is that they migrated due to climate change. When they arrived in the area now known as the Cradle of Humankind, they would have encountered P. robustus and perhaps the last of A. africanus .
H. erectus represents the first human species to be recognizably human beyond cladistics. In this way, they represent the beginning of humankind as we would physically recognize it in the Cradle of Humankind.
Four views of the LES1 Homo naledi cranium. (John Hawks, et al / CC BY 4.0)
Homo naledi was just discovered in 2015. Although it was not technically discovered in the Cradle of Humankind, it was discovered in the nearby Rising Star cave system and their range likely overlapped with what is now considered to be the Cradle of Humankind site network.
H. naledi lived from 335,000 years B.P. to 236,000 years B.P. They are unusual in that they had a mixture of human and australopithecine characteristics. Their large brains, their hands, and their feet make them look more like genus Homo. Their pelvis and shoulders make them look more like australopithecines.
So far, no tools or animal fossils have been found in association with H. naledi , so it is not clear how they lived in their cultural or ecological context. They could have represented an unusual local species of Homo or very late australopithecines. It is not clear how they are related to other human species. Nonetheless, Homo naledi shows the diversity of the hominin denizens of the Cradle of Humankind.
Inside the Maropeng Visitor Center at the Cradle of Humankind in South Africa. ( Maropeng Visitor Center )
The Amazing Legacy of Human Evolution In South Africa
The Cradle of Humankind reveals a rather different world than today. In the modern world, there is one human species, Homo sapiens , but over the two and a half million years that our genus has existed, there have been many human species adapting to different niches across the planet, including Neanderthals, Denisovans, H. floresiensis, and H. erectus .
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Many of these species coexisted at various times and in various locations. Why is there only one human species today? One possibility is that H. sapiens has so successfully adapted to their niche, that modern humans have outcompeted all other human species, leading to only one remaining Homo species. Homo sapiens continues to strain the ability of other species to adapt and survive. The modern environment is being rapidly changed by modern humans and our idiosyncratic approach to adapting to our environment through technology, a tradition that arguably started with H. erectus .
The Cradle of Humankind is a window into a past when several hominin species were at about the same level in terms of evolutionary competitiveness so that they could live in relative ecological harmony. It is possible that modern humans could do this in the future as our species becomes more conscious of its planetary-scale environmental impact and the importance of preserving biodiversity.
The Cradle of Humankind itself is an example of the impact of H. sapiens , having been subject to environmental degradation from waste-dumping, over-grazing, and other environmentally harmful practices. Just as there was a Cradle of Humankind, will there also be a grave of humankind? Uncovering human evolution to find out what we were and what we may become may give us an answer to that question.
Top image: The Cradle of Humankind visitors’ complex in Maropeng, South Africa. Source: Olga Ernst / CC BY-SA 4.0
By Caleb Strom
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