About a million and a half years ago, one of the archaic human species roaming Africa was Paranthropus boisei. They were first discovered by the anthropologist Mary Leakey in 1959, in association with primitive Oldowan-style stone tools. Since that time, argument has raged over whether or not Paranthropus actually made those tools or if the maker was another of the many contemporary hominins in Africa.
Now the first-ever discovery of a fossil hand of a Paranthropus, at Lake Turkana, Kenya, with the discovery of a partial skeleton contributes, well, something to this conundrum.
One problem in identifying the toolmaker is that when P. boisei lived, from over 2.6 million to 1.3 million years ago insofar as we know, so did several other early human species, including australopithecines and early members of the Homo genus – habilis, rudolfensis and erectus. So finding tools with a skull isn’t necessarily indicative of which species made the tools.
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Another is that while dozens of boisei skulls and teeth have been found since Leakey’s original discovery, they weren’t found with other skeletal elements. We really didn’t know what they were like, though some inferences were made from the crania.
Now for the first time, anthropologists report with confidence on hand and feet bones unambiguously associated with Paranthropus boisei. In other words, for the first time, its hands could be studied, and the results were startling.
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A Paranthropus boisei skull at the Nairobi National Museum Credit: Bjrn Christian Trrissen
A Paranthropus boisei skull at the Nairobi National Museum Credit: Bjrn Christian Trrissen
The newly reported specimen KNM-ER 101000 attests that P. boisei did share key bipedal and manipulative adaptations with the Homo genus, Carrie Mongle of Stony Brook University reported on Wednesday in Nature together with colleagues. It had some dexterity. But in other major ways its hand resembled that of an ape, as explained further in a parallel Nature paper by Tracy Kivell and Samay Syeda that compares a gorilla hand with KNM’s hand and with ours.
It’s sort of halfway. P. boisei has a long robust thumb, short, relatively straight fingers and a dexterous pinkie, just like us. In every other way, its hand is like a gorilla’s, including its sheer brute power, which the researchers say was unparalleled in the Homo sphere.
The shape of boisei’s fingers is gorilla-like. Ultimately, it could achieve handgrips similar to those of modern humans and Neanderthals – but not the dexterous precision-pinch grips that both we and Neanderthal-types do so well.
What did it do with its powerful, dexterous-but-not-pinching hands? Did it make tools? How did it live?
Vegetarian giants
Separate work postulated that P. boisei was habitually bipedal but used its powerful arms to climb trees a lot.
Mongle and her team don’t quite agree with the arboreal lifestyle hypothesis. They posit that P. boisei used its strong hands chiefly for “manual food processing” – which happily for our imaginations, speaks of stripping spines from leaves and inedible parts from plants as gorillas do, not necessarily refer ripping animals apart as we do.
Gorillas are vegetarian, while the Homo lineage has been omnivorous or largely carnivorous for at least 2 million years. Although he’s considered a relative of humans, P. boisei specifically is thought to have subsisted on vegetation and nuts, gorilla-style.
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A mountain gorilla flexing his powerful chewing muscles Credit: Charles J. Sharp
A mountain gorilla flexing his powerful chewing muscles Credit: Charles J. Sharp
Gorillas use their dexterity and strength to strip plants of indigestible spines and crack plant casings. Its face suggests P. boisei may have done the same. P. boisei had a flat face and big molars, broad cheekbones and, driving home the connection between diet and skull, some Paranthropus sub-groups featured bony ridges on the top of the skull, associated with enabling powerful chewing muscles.
So, physical anthropology postulates that P. boisei pursued a gorilla-like life eating foods that were hard to chew, including grasses, sedge and nuts and now, the new paper ties its hands into the narrative.
So what have we? A hand halfway between us and the gorilla, very powerful, and dexterous enough to have theoretically fashioned tools – and/or to process plants. The new work supports the theory that P. boisei subsisted as ecological generalists while our ancestors became more and more committed to our tools to obtain food: We all lived in the same basic environment, but had dramatically different exploitation strategies. We ate animals and supplemented them with plants. They ate plants.
Did they make the tools?
Mongle’s team points out that tool use may not have been the only factor driving selection of hand morphology, but it may have played a key role in ours. Modern humans and our extinct sister species, the Neanderthals, share derived features in the thumb and wrist that would have arisen in our ancestor, enabling the pinch grip that boisei could not achieve. And these may have evolved as an adaptation to making and using stone tools, possibly arising by as much as 1.4 million years ago.
All this goes to say that toolmaking has been around for more than 3 million years, after which time any of the hominin species could have made tools; Paranthropus boisei’s hands were unexpectedly gorilla-like and strong, but he too could have made tools. So we still don’t know who made the artifacts in Olduvai, but theoretically boisei could have, and if there’s a bottom line, it’s that gorillas and their plant-ripping lifestyle may have, as Kivell and Syeda point out, played a bigger role in our evolution than we realized.