IT ISN’T often that an esteemed professor sets out to investigate a scientific discovery made by a 15-year-old boy, but in 1938 Robert Broom made an exception. The British-born palaeontologist was keenly aware that 1930s South Africa was gaining a reputation for its exceptionally primitive-looking hominin fossils. So, when he heard that schoolchild Gert Terblanche had discovered fragments of a hominin skull in a cave there, he tracked him down immediately. Broom’s visit to the boy’s school paid off – he later recalled that the teenager was sauntering around with .
Within months, Broom had finished analysing the fossils. Deciding they were unlike anything discovered before, .
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But despite his confidence that the remains were valuable, Paranthropus never became famous. Perhaps that is because it was a misfit: it resembled one of our small-brained ancestors, but it was present on Earth long after other ape-like hominins had given way to big-brained humans. Even among palaeoanthropologists, is described as the “forgotten” hominin.
Perhaps not for much longer. Spurred on by the discovery of more fossils, researchers are finally reassessing this addition to our evolutionary tree – and their work suggests it was one of the oddest. Paranthropus may have been a skilled tool-maker, but it also potentially grazed grass like a cow and communicated with low rumbles like an elephant. The question now is, can the research bring us closer to understanding how the last of the ape-people survived in a world that was dominated by early humans?
Crudely speaking, the story of human evolution divides into two acts. Beginning about 7 million years ago, the ape-like hominins evolved, probably in Africa. They included Sahelanthropus, which may or may not have regularly walked on two legs, and Australopithecus, which did. Then, about 2.4 million years ago (or possibly a little earlier), came the human-like hominins that fall in the genus Homo. Eventually, some of these evolved into our species, Homo sapiens, probably around 300,000 years ago.
There is a straightforward pattern to this simplified story. It is one that sees hominins gradually spending less time in trees and becoming more adept at walking on the ground, while simultaneously evolving larger brains and smaller jaws and teeth.
But in this grand picture of hominin evolution, Paranthropus sticks out like a sore thumb. Its brain was similar in size to that of the ape-like hominins, and its teeth were exceptionally large. But it lived late in the story – an ape-like hominin alongside the human-like species. “We have evidence of Paranthropus from 2.8 to 1.4 million years ago,” says at Arizona State University.
It is possible that it survived even later than that, says at Campbell University in North Carolina – perhaps until 1 million years ago. That would put it on the planet at around the same time as “ancestor X”, the big-brained human species that gave rise to our species and Neanderthals. It also raises questions about why Paranthropus, a hominin with such apparently anachronistic features, evolved at all – let alone thrived for more than a million years.
Today, we know of three Paranthropus species: P. robustus in southern Africa and two further species, P. boisei and P. aethiopicus, that lived in eastern Africa. But while we have known about Paranthropus since Broom named it 85 years ago, our efforts to understand the last of the ape-people were long hampered by a lack of fossils. For decades, the only remains we had were teeth and parts of the skull and jaws. These made it clear that the features of Paranthropus were drastically different from those of contemporary human-like species, which led to some misplaced assumptions about its lifestyle.
In particular, we learned decades ago that it had “this really almost dish-shaped face that is caused by the cheekbones getting so big to allow for these huge chewing muscles”, says at Southern Cross University in New South Wales, Australia. It also had “hyper-thick enamel” and “enormous back teeth”, she says. Indeed, it has been argued that, relative to its weight, Paranthropus had the biggest jaws and teeth of any primate that ever lived. It is understandable, then, that researchers initially concluded that these ape-people dined on hard foods. The first skull of P. boisei – found by palaeoanthropologist Mary Leakey in the 1950s – actually became known as “Nutcracker Man”.
As we have learned more about Paranthropus in the past 20 years, it has become clearer that the catchy nickname isn’t really suitable. For instance, a 2021 study showed that the to see in a hominin that regularly chewed nuts and other hard foods. Instead, the growing consensus is that Paranthropus probably ate a lot of tough, chewy foods, including grasses. The evidence for this is particularly clear for P. boisei. Analyses of the carbon in their teeth show that they – which basically means grasses and the grass-like sedges. P. robustus seems to have eaten a more mixed diet, but it was still largely plant-based.
“They must have been eating these horrifically dense and tough foods,” says Green. However, they probably didn’t pass up the opportunity to eat softer foods too. “Would Paranthropus have eaten ripe fruit and delicious insects and other things that they came across? Yeah, almost certainly,” says Green. The teeth, in this view, were an adaptation “to the foods that get them through the toughest two to three months of the year”, he says. Even so, they hint at a diet that, for a hominin, was unusually specialised.
We may be closer to understanding why Paranthropus went down this evolutionary path: the triggering factor seems to have been climate change.
Parts of Africa became much drier a few million years ago, says Leece. “It was turning from a wetter, forested area into something more like what it is now – a drier, grassier landscape.” Hominins would have needed to find new sources of food, and one way to do that would be to evolve bigger teeth to eat the newly abundant grasses. “There’s this huge evolutionary pressure all of a sudden.”
So we now know that Paranthropus had an odd diet for a hominin. We have recently learned that it was unusual in other respects, too. In 2013, Manuel Domínguez-Rodrigo at Complutense University in Madrid, Spain, and his colleagues described , in the form of 1.34-million-year-old arm and leg bones found in Tanzania’s Olduvai gorge. The bones were big and chunky, confirming that it wasn’t just Paranthropus‘s teeth that were robust.
More bones appeared a few years later, discovered by Green and his colleagues at Ileret in Kenya. In a 2020 study, the researchers revealed a little more about P. boisei‘s arms, as well as providing us with a first glimpse of its hand bones. Given the “massive” upper arm bone, Green says it is likely that Paranthropus was better at climbing trees than modern humans.
“It makes sense for me,” says Reed. Paranthropus wasn’t particularly fast and had no natural armour. “How are you going to defend yourself against three different species of hyenas, sabre-toothed cats, lions, giant-sized predators?” she says. “Climb a tree.”
Elephant-like vocalisations
A further hint at its lifestyle comes from its inner ear. In 2021, at Paul Sabatier University in Toulouse, France, and his colleagues reported that compared with Australopithecus and early humans, P. robustus from a site in South Africa had distinctively shaped cochleas, the part of the ear that turns sounds into signals for the brain. The cochleas would have been . Braga suggests that Paranthropus could make low-pitched sounds, which would travel great distances. He compares them to elephants, which can make low-frequency noises and hear them from many kilometres away.
This is all quite different from anything we imagine as human: something that chewed grass like a cow, rumbled like an elephant and climbed trees like a chimpanzee. In other words, we are left with the impression that Paranthropus were nothing like our human ancestors in terms of diet and behaviour. Arguably, then, we are close to solving the mystery of how and why they survived for so long in a world increasingly dominated by humans: Paranthropus just weren’t competing with humans for food or living space.
However, recent evidence suggests the story may not be quite so simple. For one thing, it is clearer than ever that, evolutionarily speaking, these ape-people weren’t as far removed from early humans as their looks might suggest. A study published in January presented . Paranthropus emerged as one of the closest relatives to our Homo genus. In some analytical scenarios considered in the study, it was the closest.
In line with this, a study by Braga and his colleagues published in May showed that rather than Australopithecus babies. For example, the bone that housed the incisor teeth fused with the rest of the jaw during pregnancy, which is a Homo-like trait. Then there is the growing evidence that Paranthropus may have been capable of some strikingly human behaviours. In particular, they possibly used – and for all we know, perhaps even made – stone tools.
Beginning about 2.5 million years ago, at many archaeological sites in Africa, a type of stone tool known as Oldowan begins to appear. More sophisticated than any stone tools made earlier in prehistory, these were said by one archaeologist to . Intriguingly, going back decades, some of these tools have been found alongside Paranthropus remains. Even so, there has also generally been evidence that early humans were nearby too, and researchers have tended to conclude that those larger-brained early humans were the toolmakers, says Green.
This changed in February, when researchers led by at Queens College, City University of New York, described in Kenya. They were between 2.6 million and 3 million years old and had been used to process large animal carcasses and plant foods. Crucially, the artefacts are the oldest known Oldowan tools and date to a time and place where we have found few hominin remains. There were hardly any physical remains of hominins at the site – and the few teeth found belonged to Paranthropus.
As a result, the researchers argue we have to accept the possibility that Paranthropus used the tools. Perhaps a group of these ape-people found tools left by as-yet-unidentified humans who had passed through the area. Or perhaps members of the group had the mental capacity to make the tools themselves from raw lumps of stone.
Did Paranthropus use stone tools?
Some doubt that Paranthropus was capable of tool use, let alone tool production. But others argue this is largely down to our human-centric bias: Reed says that if the teeth found with the stone tools had been from early humans, no one would question identifying them as the tool-users.
“I think now the debate is around tool manufacture,” says Leece. Fashioning the sophisticated tools from lumps of unshapen rock is a cognitive challenge, requiring a degree of forward planning that it is still difficult to imagine being possible for relatively small-brained hominins like Paranthropus. But if attitudes shift and researchers begin to accept the possibility of them as a tool-maker, butchering animal carcasses on the landscape, then the behavioural distinctions between Paranthropus and early humans become blurrier – and the question of how the two co-existed opens up again.
Indeed, if anything, the fossil record suggests Paranthropus was, for a time, more successful than early humans. “Two million years ago, you would not have bet on us,” says Leece. “In sites around this time, there’s 10, 15, 20 Paranthropus specimens for every Homo specimen you find. So they were certainly more successful than our ancestors for a while.” But by 1 million years later, the roles had reversed: early humans were thriving and Paranthropus was on the way to extinction. What went wrong for the last of the ape-people?
It can be tempting to invoke violent conflict, but there is little to no evidence of early humans attacking Paranthropus. “I don’t think anybody thinks that,” says Reed. Instead, climate change may again be a factor. A found evidence that carbon dioxide levels rose between 1.3 million and 0.7 million years ago, causing P. boisei‘s favoured grasses to become less common. This shift in vegetation would have created a pressure to evolve or die.
“That would make sense,” says Leece. Paranthropus was “the mammoth of the hominins”, she suggests, referring to the latter’s presumed demise due to rapid changes to dietary flora in its habitat. “They got so far down this hyper-specialised adaptive route that when they hit another source of pressure, they weren’t able to adapt away from it quickly enough. That left them kind of cornered in a niche that was no longer viable for them.”
In contrast, early humans may have survived by becoming generalists. A study published in February compared early humans and P. boisei in Kenya between 1.4 million and 2 million years ago. . “Paranthropus turns right and starts developing all this big, specialised feeding apparatus, and our [genus] turns left and starts becoming this more generalised thing,” says Leece.
But Paranthropus wasn’t just an evolutionary dead end. For one, it is a reminder that for most of hominin history, many species coexisted. “It’s an absolute anomaly for us to be the only species of hominin on the landscape right now,” says Leece.
For another, there is still the intriguing – if speculative – idea that Paranthropus live on in all of us, having interbred with early humans and so potentially contributed small amounts of DNA to our species. They and early humans probably shared a common ancestor around 3 million years ago, and it can take a long time before seemingly separate species can no longer interbreed. “Were they capable of exchanging genetic material for 100,000 years or 200,000 years or a million years?” asks Braga. “We don’t know.” But just as later Homo sapiens interbred with Neanderthals, early humans may have interbred with Paranthropus. “I know it’s a very, very debatable idea, but we need to consider that,” says Braga.
Michael Marshall is a science writer based in Devon, UK, and author of The Genesis Quest
