a. DNH 8 occlusal view; b. DNH 8 left lateral view; c. DNH 8 inferior view; d. DNH 8 right lateral view.
Two million years ago, southern Africa was home to different human relatives sharing the same landscape and following different evolutionary trajectories. That is the picture strengthened by newly described fossils from Drimolen Main Quarry in South Africa’s Cradle of Humankind. For creationists, the difficulties begin with the date: these hominins lived almost two million years before the supposed magical creation of the Universe out of nothing in a literal reading of Genesis. But the evidence also challenges the familiar caricature of human evolution as a single procession of increasingly human creatures, marching towards a predetermined destination.
In a paper published in Annals of Human Biology, Jesse M. Martin and colleagues describe 18 previously undescribed cranial and mandibular specimens from Drimolen. Among them is DNH 127, an adult skull fragment attributed to Homo erectus. This provides valuable support for the earlier identification of DNH 134, a young child’s partial skull from the same site. Identifying a species from an immature individual can be difficult because some diagnostic features develop during growth; an adult specimen provides an additional test of that interpretation.
The significance is therefore corroboration: DNH 127 strengthens the case that Homo erectus was present in South Africa approximately 2.04–1.95 million years ago. It does not, by itself, establish that the species originated there. The earliest fossil yet recognised is evidence of a species’ presence at a particular place and time, rather than a birth certificate identifying its evolutionary birthplace.
Fourteen of the specimens are assigned to Paranthropus robustus, an extinct relative belonging to another branch of the human family tree. These remains support the interpretation that the Drimolen population differed anatomically from younger South African populations, consistent with evolutionary changes in its chewing apparatus. While Homo erectus is associated with larger brains and smaller molars, P. robustus developed increasingly powerful adaptations for chewing. Evolution was producing different combinations of traits in different lineages, with no foresight about which would ultimately leave descendants.
There is also a useful lesson here in how science works. Fossils collected years or decades ago can yield fresh evidence when researchers describe, compare and reassess them. Fragmentary remains require cautious interpretation, and the authors leave three specimens without a genus or species assignment. Such uncertainty is something to investigate openly. It provides no justification for replacing the evidence with a creation story, nor does a debate about a fossil’s precise place in the family tree make its geological antiquity disappear.
Human Evolution: A Branching Family Tree. The familiar illustration of an ape gradually straightening up until it becomes a modern human gives a misleading impression of evolution. Our history involved multiple related species, often living at the same time. Some populations gave rise to further branches; others eventually became extinct. Each evolved in response to its own circumstances, without a predetermined destination.
Two relatives sharing one landscape
At Drimolen, approximately two million years ago, Homo erectus and Paranthropus robustus inhabited the same region. They represent different branches of the hominin family tree. P. robustus is generally regarded as an extinct evolutionary cousin, rather than an ancestor of modern humans.
Powerful jaws do not reveal the whole menu
- Homo erectus: A widespread and variable species, broadly defined, with populations in Africa and Asia. More complete fossils from other sites show relatively long legs and body proportions suited to life on the ground. Populations within this broad grouping probably contributed to the ancestry of later humans, although the precise relationships remain debated.
- Paranthropus robustus: A southern African hominin with large cheek teeth, thick tooth enamel and skull features associated with powerful chewing muscles. “Robust” refers principally to this chewing apparatus, rather than an exceptionally large or muscular body.
The teeth and jaws of P. robustus indicate an ability to process mechanically demanding foods. They do not establish that it ate nothing else. Evidence from tooth wear and chemical analyses suggests dietary variety. An adaptation that helps an animal survive periods of food scarcity need not describe what it eats most of the time.
Evolution within a species
Evolution does not require every anatomical change to produce a new species. Successive populations can differ while remaining recognisably part of the same lineage. The Drimolen researchers interpret differences between its P. robustus fossils and younger South African samples as evidence of change through time in the chewing apparatus.
An alternative explanation had emphasised differences between males and females. Additional fossils allow researchers to test these competing interpretations: do the anatomical differences mainly reflect sex, or do they distinguish populations of different ages? This is how a fossil collection becomes evidence for testing evolutionary hypotheses.
A short glossary
- Hominin
- In the usage adopted here, modern humans and extinct species more closely related to us than to chimpanzees.
- Lineage
- A succession of ancestral and descendant populations through time.
- Morphology
- The form and structure of an organism or its parts, such as the shape of a skull or tooth.
- Sexual dimorphism
- Differences in physical characteristics between males and females of the same species.
- Microevolution
- Evolutionary change within populations. In fossils, changes in inherited anatomy can provide evidence of this process, even where DNA is unavailable.
- Sensu lato
- Latin for “in the broad sense”. Homo erectus sensu lato includes African fossils that some researchers classify separately as Homo ergaster.
The Drimolen research paper.
Smithsonian Human Origins profiles of Homo erectus
Smithsonian Human Origins profiles of Paranthropus robustus.
The Paper in Annals of Human Biology was the subject of an accompanying La Trobe University news release:
Fossils confirm human ancestors first appearance
La Trobe archaeologists have described 18 new hominin fossils including a second Homo erectus skull fragment confirming the species’ first appearance was in southern Africa 2.0 million years ago – 200,000 years earlier than traditionally thought.
The fossils also include representatives of another species, P. robustus, and show that it was undergoing microevolutionary change in response to climatic pressures.
The Drimolen Main Quarry in South Africa’s ‘Cradle of Humankind’ is one of the richest deposits of human ancestors in the world, yet many of the fossils excavated between its discovery in 1992 and 2019 were unpublished and therefore unknown to science.
La Trobe archaeologists, together with colleagues from South Africa and the United States, have now described a further 18 fossils from this site and attributed them to Homo erectus and P. robustus.
In a paper published today in Annals of Human Biology, the scientists reveal they have identified the first fossil from an adult Homo erectus at Drimolen, dated 2 million years old. This is 200,000 years older than other Homo erectus adult fossils found in other parts of the world like Dmanisi in Georgia which are dated at 1.8 million years old.
Homo erectus is the first species of hominin that researchers broadly agree fits within our own genus Homo and is likely directly ancestral to us. Drimolen preserves evidence for the first appearance of this species 2 million years ago, however the original fossil, DNH 134, belonged to a child aged between two and four, and there was uncertainty about what the adult version may have looked like. This paper publishes a new adult fossil attributed to Homo erectus, DNH 127, providing further confirmation that this species first appeared in southern Africa 2 million years ago.
Dr Jesse M. Martin, lead author.
Palaeoscience Labs
Department of Archaeology and History
La Trobe University
Bundoora, Australia.
The researchers have also been able to confirm that P. robustus underwent micro-evolution, and evolved larger teeth and chewing muscles between 2 million and 1.8 million years ago.
Dr Martin said while Homo erectus were evolving larger brains and smaller molar teeth, possibly associated with meat eating, P. robustus maintained a brain size slightly larger than chimpanzees and evolved massive molar teeth to process tough and hard foods - like a mortar and pestle.
These two human species shared the same landscape and are both preserved in Drimolen cave. While we know that Homo erectus and the lineage leading to us was ultimately the successful one, 2 million years ago P. robustus outnumbered Homo erectus at Drimolen by more than 10 to one. During this time period it was our ancestors that looked like the outside long-odds chance to survive. This paper confirms that the P. robustus fossils from the 2-million-year-old Drimolen Cave are slightly but importantly different from the P. Robustus fossils at the 1.8-million-year-old Swartkrans cave. During this 200,000-year period, P. Robustus teeth became even larger, and so did the muscles associated with chewing. Hominin fossils are so rare that generally the differences between them are huge, and researchers are left to make educated guesses regarding what existed in the missing parts of the fossil record. However, the large number of fossils from Drimolen, some of which are published in this paper, allow an unprecedented insight into the micro-evolutionary changes that shaped human ancestors.
Dr Jesse M. Martin.
Dr Martin said the uniqueness of the Drimolen P. Robustus population had previously been recognised with a new sub-species name, P. Robustus ukusa, and the fossils described in the research paper support this formal recognition.
The study was conducted by scientists from the Palaeoscience Labs, Department of Archaeology and History, La Trobe University, Palaeo-Research Institute, University of Johannesburg, Evolutionary Studies Institute, University of the Witwatersrand, and Department of Anthropology, Washington University.
Publication:
The Drimolen fossils add another piece to a human history extending far beyond anything allowed by a literal reading of Genesis. Approximately two million years ago, different hominin lineages were already sharing southern Africa and evolving along different paths. Whether future research revises the precise classification of an individual fragment will not make that ancient landscape, or its inhabitants, fit into a Universe supposedly created a few thousand years ago with a human species magically created without ancestry.
These findings also expose the weakness of the creationist caricature of evolution as a ladder with modern humans waiting at the top. Paranthropus robustus was not an unsuccessful attempt to make Homo sapiens. It was a member of a distinct lineage, with adaptations that enabled its populations to survive and reproduce in their own environments. Nor was the eventual emergence of our species something evolution anticipated. Natural selection has no knowledge of future conditions: it acts on existing variation, while environmental change and chance help determine which populations persist.
The scientific value of DNH 127 lies in the additional evidence it provides for an interpretation already proposed from a juvenile skull. Likewise, the newly described Paranthropus material allows competing explanations of anatomical differences to face further tests. This is the practical work of evolutionary science: comparing specimens, testing predictions and adjusting conclusions to accommodate the evidence. Acknowledging uncertainty about fragmentary fossils makes those conclusions more defensible, because it distinguishes what the evidence supports from what remains unresolved.
For young-Earth creationism, the problem remains the accumulated evidence of deep time and a branching, changing human family. Disputing which twig a particular fossil belongs on does nothing to explain away the tree. The rocks and fossils record populations living, varying and evolving long before the supposed Creation Week, with no scientific need to invoke a plan, a predetermined human destination or a magical creation event.
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