Earliest sign of a sense of aesthetics

Maybe because of the Covid-19 pandemic, there has been a dearth of interesting new developments in the geosciences over that last few months: the ‘bread and butter’ of Earth-logs. So instead of allowing a gap in articles to develop, and as a sign that I haven’t succumbed, this piece concerns one of the most intriguing discoveries in palaeoanthropology. In 1925 Wilfred Eitzman, a school teacher, investigated a cave in the Makapansgat Valley in Limpopo Province, South Africa that had been exposed by quarry workers.  His most striking discovery was a polished pebble made of very fine-grained, iron-rich silica, probably from a Precambrian banded iron formation. Being round and deeply pitted, it had clearly been subject to prolonged rolling and sand blasting in running water and wind. Eerily, whichever way it was viewed it bore a striking resemblance to a primate face: eyes, mouth, nose and, viewed from the rear, a disturbing, toothless grin. We have all picked up odd-looking pebbles on beaches or a river bank: I recently found a sandstone demon-cat (it even has pointy ears) when digging a new vegetable patch.

The Makapansgat Pebble. Inverted it still resembles a face and its obverse side does too.

What is different about the Makapansgat Pebble is that Eitzman found it in a cave-floor layer full of bones, including those of australopithecines. The cave is located in dolomitic limestone outcrops high in the local drainage system, so it’s unlikely that the pebble was washed into it. The nearest occurrence of banded iron formation is about 20 kilometres away, so something must have carried the pebble for a day or more to the cave. The local area has since yielded a superb palaeontological record of early hominin evolution, stimulated by  Eitzman’s finds. He gave the fossils and the pebble to Raymond Dart, the pioneer of South African palaeoanthropology. Dart named the hominin fossils Australopithecus prometheus because associated bones of other animals were covered in black stains that Dart eagerly regarded as signs of burning and thus cooking. When it became clear that the stains were of manganese oxide the name was changed to Au. africanus, the fossils eventually being dated to around 3 million years ago.

Dart was notorious for his showmanship, and the fossils and the Makapansgat Pebble ‘did the rounds’ and continue to do so. In 2016 the pebble was displayed with a golden rhino, a collection of apartheid-era badges and much more in the British Museum’s South Africa: the art of a nation exhibition. Well, is the pebble art? As it shows no evidence of deliberate working it can not be considered art, but could be termed an objet trouvé. That is, an ‘object found by chance and held to have aesthetic value to an artist’. The pebble’s original finder 3 million years ago must have found the 0.25 kg pebble sufficiently interesting to have carried it back to the cave, presumably because of its clear resemblance to a hominin head: in fact a multiple-faced head. Was it carried by a cave-dwelling australopithecine or an early member of genus Homo who left no other trace at Makapansgat? At an even earlier time a so-far undiscovered hominin did indeed make simple stone tools to dismember joints of meat on the shores of Lake Turkana in Kenya. It is impossible to know who for sure carried the pebble, nor to know why. Yet all living primates are curious creatures, so it is far from impossible that any member of the hominins in our line of descent would have collected portable curiosities.

Eats barks leaves nuts and fruits

English: The Malapa site valley, looking North...
The Malapa valley South Africa, where Australopithecus sediba was found. (Credit: Lee R. Berger via Wikipedia)

The first stone tools and bones that had been cut by them, found in rocks  dated at 2.5-2.6 Ma in the Bouri area of Ethiopia’s Afar Depression, have generally been taken as a sign that their invention was connected with more easily accessing meat for food. A corollary of this idea is that it was the introduction of meat into the hominin diet that helped ‘fuel’ the growth of their brains: meat-tools-brain interrelated in an evolutionary sense. There is a spatial link between such  tools and fossils of Australopithecus, but direct attribution of the tools to these australopithecines  has not been widely accepted. It is more generally accepted that a link to tools can be made with Homo habilis, but they lived, at the earliest, 200 to 300 ka later. The wear patterns on their teeth and association with animal bones bearing cut marks has been taken to indicate that at least part of their diet was meat.

Another approach to diet is to analyse the proportions of stable carbon isotopes (13C and 12C) in tooth enamel, which can discriminate between the ultimate plant source in their diet, i.e. between grasses that use  the C4 photosynthetic pathway and the C3 version used by woody and herbaceous plants. The isotopic ‘signature’ of plants is also passed on to animals, depending on what vegetation they eat, and so up the food chain to predators and the scavengers that depend on their leavings. South African Au. africanus of around 2.5 Ma ago show a definite  C4 preference as do local paranthropoids (‘robust’ australopithecine-like creatures) from around 1.8 Ma. The early humans H. habilis and H. ergaster also show the C4 isotopic proportions, which in both cases may be from a meaty diet or from a vegetarian component. The main point from these similar results, whatever the plant-meat proportions being consumed, is that these hominins were very different from chimpanzees in their eating habits, and probably as regards their habitats: savannah rather than woodlands respectively.

There are no reports of C-isotope research on Au. garhi teeth, but results from 2 Ma old Au. sediba found in South Africa have just been published (Henry, A.G and 8 others 2012. The diet of Australopithecus sediba, Nature, v. 487, p. 90-93) along with plant materials from dental plaque and tooth wear patterns. Au. sediba is notable for its very modern-looking hands and other ‘advanced’ features. Some believe it to have been closer to the direct line of human descent than a number of other hominin species, including the poor quality remains of H. habilis. So, did sediba eat meat? The forensic evidence suggests something unexpected. The C-isotope data points towards food dominated by C3 plants – less grasses and sedges, and more shrubbery. Tooth wear suggests bark was eaten, while plant remains from plaque indicate fruit leaves and wood. This is a feeding pattern more like that of chimpanzees than Homo species, Au. africanus and the paranthropoids  that are roughly contemporary with Au. sediba. Ecological analysis of the sediments which buried the hominin specimens suggest a seasonal climate and savannah biome with abundant C4 plants that supported grazing herds, mixed with possibly some denser woodland along drainages. This is a pattern familiar from living savannah chimpanzee bands.

English: The hand and forearm of Australopithe...
The hand and forearm of Australopithecus sediba (Credit: Peter Schmid, courtesy Lee R. Berger via Wikipedia)

So, despite being an ‘advanced’ hominin, by carrying clear signs of foods that were not consumed by meaty potential prey animals Au. sediba probably was not a meat eater. Yet species with strong C4 ‘signatures’ cannot be assigned to carnivory on C-isotope  evidence alone. One has to decide from other data, such as tooth-wear and plaque, whether this or that hominin ate grasses, those that clearly did not becoming candidates for dominantly meat-eating. How to detect a tool-using species with a mixed diet, akin to more modern humans, is a tough nut to crack.

Another candidate for earliest, direct human ancestor

The cranium of Malapa Hominid 1, Holotype of A...
The head of Australopithecus sediba. Image via Wikipedia

In May 2010 EPN commented on a new find from the famous fossil-rich caves of north-eastern South Africa; a new hominin species called Australopithecus sediba. At least one of them fell into a deathtrap shaft, died and remained unchewed without bones being spread far and wide. Inevitably, near-complete skeletons of individual hominins are soon pored over by dozens of specialists in human evolution, as they were for the much older Ardepithecus ramidus found in sediments of Ethiopia’s Afar Depression (see Early hominin takes over Science magazine in the November 2009 issue of EPN). Now there are two near-complete, well-preserved skeletons of Au. sediba and the palaeoanthropological world is agog. Dating to about 1.98 Ma the specimens represent the same time as do far less impressive remains of H habilis from Tanzania that were found with associated rudimentary stone tools. The first hint (just a fragment of upper jaw) of any remains that might be tagged ‘Homo’ dates to 2.3 Ma and is from Ethiopia, as are the first undoubted stone tools going back as far as 2.5 Ma, though lacking association with a maker.

Five consecutive papers on Au. Sediba occupy 22 pages in the 9 September 2011 issue of Science and make for startling reading. The first concerns the shape of its brain case, and therefore crudely its brain, discerned by tomographic X-ray scanning (Carlson, K.J. et al. 2011. The endocast of MH1, Australopithecus sediba. Science, v. 333, p. 1402-1407). It isn’t any bigger than that of other members of the genus but shows ‘some foreshadowing of the human frontal lobes’ and other shifts from the basic ape model that the authors imply are en route to human features. The next considers the two pelvis regions (Kibii, J.M. et al. 2011. A partial pelvis of Australopithecus sediba. Science, v. 333, p. 1407-1411); again australopithecine-like in the small size of the birth canal but with a hint of the S-shape of humans. Most astonishingly well-preserved are the fragile bones of a complete hand (Kivell, T.L.  et al. 2011. Australopithecus sediba hand demonstrates mosaic evolution of locomotor and manipulative abilities. Science, v. 333, p. 1411-1417), which convincingly shows the long thumb and short fingers (for a primate) that characterise Homo and are essential for a precision grip and making things. Actually, the thumb is longer relative to fingers (60%) than in humans (54%), but Lucy’s (Au. afarensis) was a closer match. No tools that such a hand might have created and wielded were found with the fossils. Then there is the foot (Zipfel, B. et al. 2011. The foot and ankle of Australopithecus sediba. Science, v. 333, p. 1417-1420), which, again, mixes human and australopithecine features, giving ‘a unique form of bipedality and some degree of arboreality’. The fifth paper (Pickering, R. et al. 2011. Australopithecus sediba at 1.977 Ma and implications for the origins of the genus Homo. Science, v. 333, p. 1417-1420) is as remarkable for the precision of U-Pb dating of speleothem (cave carbonates), which at 1.977+0.002 Ma far exceeds the workhorse Ar-Ar method used for most other hominins, as it is for the absolute age that precedes that of undisputed remains of humans.

In short, for Australopithecus sediba there is an embarrassment of riches unmatched until those of the 1.5 Ma old H. erectus (‘Turkana Boy’) found at Nariokotome in NW Kenya. To some extent this throws a flock of peregrines in among the palaeoanthropology pigeons, as an account of a meeting earlier in 2011, at which the bones were grandstanded, shows (Gibbons, A. 2011. Skeletons present an exquisite paleo-puzzle. Science, v. 333, p. 1370). Naturally, the authors are making the most of their material especially, it seems, its finder Lee Berger of the University of Witwatersrand, South Africa, the last author in all the papers. Comparisons with more australopithecine remains were said to be needed. The soon-to-be-famous hand has been said to be essentially like others from the same genus. While the remains of the creature’s pelvis could imply that its evolution was more driven by a need for efficient upright walking than to birth big-headed babies, the ankle shows a primitive trait that would have forced Australopithecus sediba to walk strangely as the heel bone is small and angled unlike that in human feet, which is broad and flat. But all the species’s features are combined in two near-complete individuals, whereas for the rest of its contemporaries, predecessors and near successors in time speculation is based on fragments of several individuals, none more so than in the case of the earliest agreed human, near contemporaneous H. habilis, which barely stands up to taxonomic scrutiny (Gibbons, A. 2011. Who was Homo habilis – and was it really Homo?  Science, v. 332, p. 1370-1371). Some would say that it was only the associated stone tools that assigned ‘Handy Man’ to more elevated status than slightly large-headed australopithecine. The fact is; stone tools were around since 2.5 Ma, at least in Ethiopia, and this newly found being could have handled them and even made them with its palpable dexterity. Finding tools and skeletons together is almost as rare as hens with teeth…