The longest ‘age’ in human history is the first, called the Palaeolithic or Old Stone Age. It starts with the oldest stone tools we have found so far, from Lomekwi in Kenya, which are 3.3 million years old. The age ends with the beginning of the Mesolithic or Middle Stone Age in the Middle East about 20,000 years ago.
A recent discovery in Africa, however, suggests we’ve got the title wrong. It shouldn’t be the Old Stone Age, but the Old Wood Age.
Wood does not preserve well, especially compared to bone and stone, so there is little evidence for its use in the palaeoanthropological record, and what evidence there is often inferred by small cuts or nicks.
However, in an article[i] published in Nature in September last year, Barham et al describe the discovery of the first structural use of wood predating the arrival of Homo sapiens by at least 100,000 years. Waterlogged deposits at Kalambo Falls in Zambia preserved ‘two interlocking logs joined transversely by an intentional cut notch.’
The bushwillow logs, as discovered. Photograph: Banham et al, Nature (2023)
The logs, made from bushwillow, were dated by luminescence to be 476,000 years old, give or take 23,000 years.
It’s a remarkable discovery, and confirms that our ancestors (in this case probably H. heidelbergensis[ii]), were as adept at using and shaping wood as they were at using and shaping stone. Given the preponderance of wood in the environment compared to usable stone, and given its comparative softness and adaptability, this doesn’t come as a surprise, but nonetheless it’s nice to have some demonstrably worked specimens.
Wood was almost certainly the first product hominins used to make tools, from scrapers to spears. Indeed, it may have been the dominant raw material for toolmaking throughout most of human history.
So maybe the first human ‘age’ should be referred to as the Old Wood Age, with stone making the occasional guest appearance?
One of the great palaeoanthropological bombshells of the last generation was the discovery of Homo floresiensis on the Indonesian island of Flores. For years scientists debated what ancestor this new and somewhat diminutive hominin – dubbed the ‘Hobbit’ by the media – had come from, or indeed if it should even be included in our genus.
Homo floresiensis reconstruction. Courtesy of Creative Commons. This image created by ATOR.
While now generally accepted as a member of our broader tribe, its origins are still fiercely argued, many insisting it’s nothing more than H. erectus that’s undergone insular dwarfism. But I think a 2017 paper written by Colin Groves, Debbie Argue, Michael Lee and William Jungers, convincingly demonstrates that H. floresiensis is not derived from H. erectus (or is a diseased example of H. sapiens), but rather from a much earlier hominim such as H. habilis or a sister species.[i]
A second paper, published in 2020[ii], backs up this hypothesis, and concludes with this statement:
‘ … something which on account of our inadequate current taxonomic framework we have to call “early Homo” differentiated in Africa, possibly as early as 2.8 (mya) … Subsequently, one or more members of this group reached the Mediterranean fringe and spread Out of Africa at 2.5 Ma. After successfully expanding over Asia, at least one of those hominins … gave rise to new species that reached the Caucasus by around 1.8 (mya), and thence Europe by ca. 0.9 (mya) … (the) eastward expansion (or occupation) in Asia of small-bodied and archaically-proportioned hominins continued, possibly in multiple waves; and, by ca. 0.8 (mya), representatives of this group had penetrated as far as insular southeast Asia, where H. floresiensis ultimately emerged … ’
Indeed, some scientists considered this possibility as early as 2005. A report about the brain of H. floresiensis published in Science in that year[iii] concludes with these lines: ‘Although it is possible that H. floresiensis represented an endemic island dwarf that, over time, became subject to unusual allometric constraints, an alternative hypothesis is that H. erectus and H. floresiensis may have shared a common ancestor that was an unknown small-bodied and small-brained hominin.’
Homo habilis. Courtesy of Creative Commons. Photographer unknown.
I think an increasing weight of evidence strongly suggests that the first major exodus of our genus from Africa was carried out by H. habilis or one or more of her sisters. Furthermore, I think it’s possible that these closely related species then gave rise to H. erectus, H. pekinensis, H. luzonensis[iv] and H. floresiensis in Eurasia, while those remaining in Africa gave rise to H. ergaster. This does not preclude the possibility, or perhaps probability, of any or all of these species crossbreeding if they ran across each other.
But what of H. sapiens, our own species? As with H. ergaster and H. erectus, the evidence here is convoluted, confusing and often contradictory.
Mongrel
For those, like Colin Groves, who think H. ergaster is a species in its own right, the line of descent works something like the following.
Homo heidelbergensis. Courtesy of Creative Commons. This image created by ATOR.
About 600,000 years ago, H. ergaster, either directly or through an intermediary species called H. rhodesiensis, gave rise to H. heidelbergensis. This species was our size physically, and his brain capacity was well inside the standards of Anatomically Modern Humans (AMH). Following the great tradition of hominin migration, something that seems as ingrained in our genus as bipedalism, some members of this new species moved to Europe[v]. About 400,000 years ago, they gave rise to H. neanderthalensis. In a case of ‘well, we’ll show you’, those who stayed behind in Africa gave rise to H. sapiens at least 300,000 years ago, and possibly as long as 350,000 years ago.[vi]
I can’t stress this enough. Homo sapiens are Africans. It is where our archaic ancestors and AMH first appear[vii]. (Let me also stress that this story, as complicated as it gets from now on, does not resurrect the Multiregional Model for our evolution, where H. erectus gave rise to H. sapiens across its whole range at the same time, from Africa to Asia. This is an old theory, now largely discredited by the extensive fossil and DNA evidence that our species first evolved in Africa.[viii])
What happened next has been slowly and painstakingly uncovered by palaeoanthropologists doing field work throughout Africa and Eurasia, and by the outstanding work performed at the Max Planck Institute’s Department of Evolutionary Genetics, headed up by Svante Pääbo, into hominin DNA.[ix]
What the DNA evidence strongly suggests is that H. sapiens successfully left Africa between 70,000 and 100,000 years ago. (Although this wasn’t the first migration into Eurasia by our species. It is usually held that previous attempts left no trace in the DNA of AMH outside of Africa, but see these earlier posts, here and here.)
Female Homo neanderthalensis. Courtesy of PLOS ONE.
Members of the most recent migration interbred with H. neanderthalensis, probably in what is now the Middle East, and later with the Denisovans, another possible descendant of H. heidelbergensis, deeper in Eurasia[x]. To this day, the average ex-African H. sapiens carries between 1%-2% of the Neanderthal genome; but it is not the same one or two percent: we overlap. Overall, we carry up to 40% of the Neanderthal genome in our own genes. But the story gets more complex still: the genome of people from Oceania, such as Papuan New Guineans and Australian Aborigines, can have between 5-6% Denisovan DNA[xi]; indeed, recent research suggests that Ayta Magbukon Negritos in the Philippines have Denisovan ancestry 30-40% higher than either of these two groups.
The Natural History Museum of London’s Professor Chris Stringer says, ‘It is now clear there was a lot more interbreeding between ancient species, including early Homo sapiens and others, and that there was a lot more movement of populations both in the distant past – and relatively recently.’[xii]
Homo sapiens (Oase 2) reconstructed from bones 37,000-42,000 years old discovered in the cave of Peştera cu Oase in Romania. Around 7.3% of his DNA is from H. neanderthalensis, from an ancestor 4-6 generations back. Courtesy of Creative Commons. Photo: Daniela Hitzemann.
Talking about recent research, in June last year Chinese scientists announced that a cranium first discovered in China almost a century ago, is a new species of Homo with a brain easily the equal of any AMH in size and carried inside a skull more massive than ours. Those making the announcement have named the new species H. longi (‘Dragon man’, and just as Denisovans are sometimes described as a sister species to Neanderthal, so H. longi is being claimed as a sister species to H. sapiens[xiii]).
As Lee Berger, from the University of Witwatersrand and the discoverer of Australopithecus sediba and H. naledi, has suggested, perhaps the different paths of human evolution are not best thought of as branches spreading from a single tree trunk, or even a messy, many-twigged bush, but rather a braided stream[xiv] with tributaries constantly running across each other before separating, rejoining and separating once more.
The Waimakariri River in New Zealand is braided along almost its entire length. A good metaphor for hominin interbreeding? Courtesy of Creative Commons. Photo: Greg O’Beirne.
We, Anatomically Modern Humans, are the result of all this evolution. We are nothing more than a mongrel species.
And this from the Australian Museum: ‘Most scientists that accept H. floresiensis as a legitimate species now think its ancestor may have come from an early African dispersal by a primitive Homo species similar in appearance to H. habilis or the Dmanisi hominins. This means that it shared a common ancestor with Asian H. erectus but was not descended from it. Cladistic analysis supports the lack of a close relationship with H. erectus.’
[v] The first H. heidelbergensis fossils were found near Heidelberg in 1907.
[vi] Although this paper suggests the split between our two species might be found much further back … up to 800,000 kya or more!
[vii]Recent research from scientists at Australia’s Garvan Institute of Medical Research reveals that southern Africa is home to the oldest evidence for AMH: ‘… to contemporary populations that represent the earliest branch of human genetic phylogeny.’ The date they arrive at is 200,000 years ago.
As well, a report in the February issue of Science describes how thousands of genome sequences were collected from modern and ancient humans to create a family tree. In the words of the report’s first author, Anthony Wilder Wohns, ‘ … we definitely see overwhelming evidence of the Out-of-Africa event … ‘
[viii] See Stringer, C. & Andrews, P. The Complete World of Human Evolution. London, 2011. P 140 ff for a discussion of the two main theories for the evolution of Home sapiens: ‘Multiregional’ and ‘Out of Africa’.
[ix] And now, besides DNA, they are using protein analysis to identify ancient hominins, most recently the first Denisovan found outside of the Denisova Cave in Siberia … on the Tibetan Plateau of all places! See https://www.nature.com/articles/s41586-019-1139-x, 16 May 2019.
[x]Very recently, H. sapiens remains were discovered in the Grotte Mandrin rock shelter in the Rhône Valley in France that date back 54,000 years ago, pushing back our species arrival in Europe by at leat 10,000 years from previous estimates.
[xi] Please watch this fascinating talk Svante Pääbo gave at the University of California in 2018 after receiving the Nierenberg Award for Science in the Public Interest. It goes into all of this in much more detail. As Pääbo points out in the talk, the DNA evidence indicates humans ‘have always mixed’.
Humans walk upright, gorillas and chimpanzees walk on all fours, resting their weight on their knuckles, and orangutans can do just about anything – they hang and swing by their arms from branches, sometimes with the help of their oddly-shaped feet, and on the ground they can walk either upright or on all fours. The structure of the postcranial skeleton in all four animals is very different and reflects these locomotor patterns. Non-human great apes have short legs and long arms, whereas we have very long legs. With the gorilla and chimpanzee it is the shortness of the legs that differs from humans, the arms being much more similar in length compared to the torso; only the orangutan has enormously lengthened arms. When other great apes stand upright, their legs are straight from hip to ground, whereas humans are ‘knock-kneed’, as the thighs slope inward from the hip to the knee. The pelvis is very different in appearance: in humans the hip bone (ilium) is low and very broad, but in great apes it is high and fairly narrow. In humans the great toe is long and stout and aligned with the other toes, but in great apes it is divergent from the other toes (less in the gorilla), and in the orangutan it is very short.
Courtesy of Creative Commons. Artist unknown.
In most great apes, the spinal column is more or less straight, but in humans the spine is curved into a double-S: the cervical (neck) vertebrae curve forward, the thoracic (chest) vertebrae curve backward, the lumbar vertebrae (those in the small of the back) curve forward again, the sacral vertebrae (which are fused together, and form the back wall of the pelvis) curve back again, and the coccyx (the partially fused vertebrae which are the tiny remnant of the tail) curves forward once more. The ribs (which are very variable in number, but average 12 in humans and orangutans, and 13 in chimpanzees and gorillas) together form the thorax; in humans the thorax is barrel-shaped (narrow at the top, broad in the middle, narrower again at the bottom), whereas in great apes it is funnel-shaped (narrow at the top, and broadening towards the bottom).
All of these differences between humans and the other great apes are developments stemming from bipedalism. So why did humans adopt bipedalism? Well, walk with me and we’ll take a brief look at the major theories.
Doing a runner
There seems to be a growing consensus among many scientists that our ancestors evolved bipedalism for several reasons rather than one overriding factor. What many of the competing theories do agree on, however, is that rainforest giving way to savannah because of climate change around 7.0 – 5.0 mya was a strong influence. Grassland with only scattered trees and no closed canopy meant tree-climbing primates had much more open territory to cover. Walking on two legs freed hands to carry infants, food or tools, including weapons. Walking on two legs made us taller, meaning we could locate food, potential predators and safe havens from further away; it also made it easier to pick low-hanging ripe fruit from trees. Walking reduced the amount of body surface area we exposed to the sun while in the open.
Early morning on the savannah. The change in the landscape from rainforest to savannah between 7 mya to 5 mya probably helped kickstart bipedalism in hominins. Photo: Simon Brown.
Of course, in some circumstances some of these ‘advantages’ could become disadvantages. For example, although bipedalism meant we could locate a predator from further away, it also meant if it was looking in the right direction, a predator could see us from further away as well (and our chief predators – leopards, hyenas and lions – all have good eyesight, not to mention excellent hearing and sense of smell). On the other hand, when our ancestors became active hunters, our extra height gave us an advantage over prey animals, many of whom rely on their sense of smell rather than their eyesight.
Our genus has evolved to become a natural endurance runner, and through that a natural persistence hunter. Courtesy of Creative Commons. Photographer unknown.
More recently, one of the major arguments for the successful adaptation of bipedalism was that it is a much more energy efficient method of locomotion[i]. Whatever the arguments for or against all these hypotheses regarding the origins of walking, when it came to running there is no denying our bodies evolved to make us one of nature’s supreme endurance runners[ii]. This seems to have happened about two million years ago and was a real game-changer when it came to predating: our ancestors evolved into persistence hunters, able to wear down much larger animals such as kudu and oryx[iii]. Basically, humans ran their prey into the ground, and much of our body shape is particularly adapted to long-distance running.
In other words, the characteristics that make us superb walkers and runners are the characteristics that most set us apart from other great apes. As Chris Stringer and Peter Andrews write in The Complete World of Human Evolution, ‘at present … (bipedalism) is taken as the earliest adaptation by which we can recognise human ancestors in the fossil record.’[iv]
The odd-sock drawer
Now it’s time to deal with one of the most controversial species in the human lineage – Homo ergaster. This species was described by Colin Groves and Vratislav Mazák in 1975[v]. Since then, palaeoanthropologists are divided on whether H. ergaster is a distinct species, or a subspecies belonging to H. erectus, palaeoanthropology’s pin-up boy and all-purpose species.
Once they learned to walk, our ancestors just kept on walking. In fact, they walked right out of Africa, into the Middle East, then east into Asia and Sahul, north to Europe, and eventually across the Bering Strait and into the Americas. On the way they continued evolving into new species that seemed to interbreed with each other at every opportunity, creating yet more new species, and eventually discovering agriculture, television and the internet. And interestingly, it’s the use of technology that provides us one piece of evidence that H. ergaster and H. erectus were two different species.
But first, let’s talk more about bones, specifically those belonging to the original H. erectus, parts of which were first discovered 1891 by Eugène Dubois, a Dutch doctor working for the army in Java. In fact, he went to Java with the objective of discovering evidence supporting the theory that H. sapiens evolved in Asia, an idea most determinedly supported by German naturalist Ernst Haeckel. Haeckel had hypothesised that our species’ progenitor, which he names Pithecanthropus alalus, had evolved on Lemuria, a mythical continent that subsequently sunk beneath the Indian Ocean (thereby conveniently leaving no fossils behind to prove – or for that matter, disprove – his theory).
Eugène Dubois, discover of Homo erectus. Courtesy of Creative Commons. Photographer unknown.
Although Dubois had discovered ancient hominin fossils, he found little or no support among scientists in Europe that they amounted to anything significant. It wasn’t until Sinanthropus pekinensis was discovered in China over a quarter-century later that enthusiasm for Dubois’s discovery really picked up. In the early 1950s, Ernst Mayer reclassified both P. alalus and S. pekinensis as H. erectus[vi]. Since then, hominin fossils with roughly the same estimated brain size as H. erectus and aged between 2 million years old to just over 100,000 years old have been thrown in with H. erectus like differently coloured socks thrown into an odd-sock draw. It has become the species to have when you want to cover all of Africa and Eurasia and two million years of history.
In the early 1970s, for example, Richard Leakey and Alan Walker described two partial skulls found in Kenya as belonging to an African offshoot of H. erectus based on the fact that their calculated brain capacities (848 cc and 803 cc) were not dramatically smaller than that of some H. erectus skulls (around 950 cc), which is like arguing that since the Volvo S60 and the Volkswagen Passat have similar interior space, they’re both examples of a Toyota Camry.
However, in 1975, Colin Groves and Czech colleague Vratislav Mazák, after a comprehensive metric analysis of fossils from Koobi Fora, discovered they had uncovered a new species they names H. ergaster. Their argument was that there was no African version of H. erectus; further, Colin Groves believed that H. ergaster evolved in Africa and then migrated into Eurasia, eventually giving rise to H. erectus.[vii] The earliest dates for the new species goes back 1.9 million years[viii], as opposed to 1.6 million years (or 1.8 according to some estimates) for H. erectus, making H. ergaster the first truly human-looking hominin to stride the planet – tall, thin, decidedly bipedal, with a flatter face than its ancestors and an active hunter, fire-user and tool-maker.
KNMER 3733, possible cranium of a female Homo ergaster. Photo: Simon Brown.
Now, nearly fifty years after the initial paper by Groves and Mazák, a fierce debate still continues between those who think the two hominins are separate if linked species, or just subspecies. In common parlance, it’s a debate between splitters and lumpers.[ix]
But besides the obvious difference in the skull shapes of H. ergaster and H. erectus, another line of evidence convinces me that Colin was right in his opinion that we are talking about two species. This evidence involves tool making.
Out with the old, in with the new
Until the appearance of H. sapiens and H. neanderthalensis, stone age technology is divided into two broad and overlapping stages: Oldowan and Acheulean (sometimes called Modes 1 and 2). Oldowan technology was first discovered in the 1930s by Louis Leakey at the Olduvai Gorge in Tanzania. The oldest examples have been found at Gona in Ethiopia, and date back about 2.5 million years[x]. The technology seems to have spread very quickly, and recent discoveries have found stone tools in Jordan dated at 2.5 mya and China at 2.1 mya[xi]. This technology, the use of very simple flakes and rocks, had been developed before the appearance of H. habilis, possibly by Australopithecus garhi. Acheulean technology which started about 1.76 mya, is closely associated with the appearance of H. ergaster and involves more refined knapping and the development of specialised tools such as hand axes.
This doesn’t imply that Oldowan technology suddenly evaporated, and every hominin adopted the new style of knapping chert. In some places, Oldowan and Acheulean stone tools are found at the same site from the same period, suggesting that while H. ergaster or one of its descendants employed the improved technology, one of our cousins continued using the older method. But it’s clear Acheulean technology obviously conferred a significant advantage over the old style. It didn’t take long for it to spread beyond Africa, either because H. ergaster itself started spreading beyond Africa, or because it spread by ‘word-of-mouth’: neighbouring hominis picked up on the new fashion of making tools and copied it. Acheulean tools appear in what is now India, for example, by 1.5 mya, and in Europe by about 900 kya.
Acheulean hand axes. Compare the careful knapping done here to the more primitive Oldowan tools illustrated in the previous post. Courtesy of Creative Commons. Photographer unknown.
However, Acheulean technology did not seem to reach Java, where our friend H. erectus resided.
Which presents lumpers with a problem. If H. ergaster is indeed nothing more than a subspecies of H. erectus, then fossil evidence suggests this single species arose in Africa before spreading throughout Eurasia. Yet if this is also the species that developed Acheulean technology soon after evolving, why didn’t the technology travel with them to the far east?
On the other hand, if we are talking about two species, then it’s quite possible for Acheulean technology to be developed by H. ergaster in Africa, spread slowly throughout Eurasia, but never quite reach the home of H. erectus in Java.
If this was in fact the case, it raises a more important question: even if we accept H. ergaster is a separate and earlier species than H. erectus. Does it necessarily follow that H. ergaster gave rise to H. erectus? What if the two species are cousins rather than mother and daughter?
This is something we’ll discuss in the next, and final, post of ‘Us’.
‘(He) was the first to suggest that the genus Pithecanthropus should be subsumed into Homo, and in the same paper he proposed that fossils recovered from what was then called Choukoutien (now called Zhoukoudian), which were initially assigned to Sinanthropus pekinensis,26 should also be transferred to H. erectus.’
‘A growing number of scientists have redefined the species Homo erectus so that it now contains only east Asian fossils. Many of the older African fossils formerly known as Homo erectus have now been placed into a separate species, Homo ergaster and this species is considered to be ancestral to Homo erectus. The redefined Homo erectus is now generally believed to be a side branch on our family tree whereas Homo ergaster is now viewed as one of our direct ancestors. ‘
[viii] Oldest fossil dates according to the Australian Museum for H. ergasterhere and for H. erectushere. Recent work reported in the journal Science may push the dates even further back, between 1.95-2.04 mya (although in this paper the discussed specimen is describe as preserving ‘characters that align it morphologically with H. erectus sensu lato (including Homo ergaster)’. Go figure.
[ix] For a fuller description of the often heated debate about what makes a species, see here.
[x] Stringer, C. & Andrews, P. The Complete World of Human Evolution. London, 2011. P 208.
A new kind of stone age technology – Lomekwian – has been suggested after the recent discovery of stone tools at Lomekwi that predates Oldowan by more than 700,000 years. See the previous post for more details.
Forgive the pun, but for decades it seemed a no-brainer that the chief qualification to be considered human was the size of your brain. Obviously, it had to be a of a certain respectable capacity, never quite defined, but a degree or two larger than a chimpanzee’s organ was a good start. There was some embarrassment when it was determined that the average brain capacity of Homo neanderthalensis was larger than our own[i], but that misgiving aside it was assumed that if not a directly comparative intelligence was a prerequisite, then certainly something within shooting distance.
One mistaken assumption here is between brain size and intelligence, something made very clear in recent years by the discovery of the stone tool-making H. floresiensis (with a brain the size of a chimpanzee). Recent work done on corvids, for example, suggests that ravens and crows possess a Theory of Mind[ii] – the capacity to imagine that another crow might have its own thoughts – which in turn suggested a reasonably developed sense of self-awareness, an emergent property traditionally associated with intelligence[iii].
Homo heidelbergensis had a brain around 1200 cc, well within the range of H. sapiens. Photo: Simon Brown.
Another mistaken assumption is that our larger brain size is extraordinary among our cousins, but average brain size has not increased dramatically in total capacity since H. heidelbergensis, a species that first saw light of day 600,000 years ago.[iv]
Indeed, Homo species sit comfortably on the line that matches a generic primate’s brain size to its body size. In other words, if you’re a primate, the bigger you are the bigger your brain gets. (This isn’t peculiar to primates, of course, and applies to many mammalian groups, eg rodents, elephants and aardvarks, but primates do have larger brains than mammals of similar body mass).[v]
Interestingly, there are three exceptions to this general rule, all three of which are closer to us genetically than any other primates: the orangutan, the chimpanzee and the gorilla. The orangutan falls just below the curve, the chimpanzee falls a little further, and the gorilla furthest of all. Extensive studies with chimpanzees and gorillas, however, show that both species are intelligent and self-aware enough to have developed a Theory of Mind.
Demonstrably, brain size is not irretrievably married to a set physical size, just as brain size is not irretrievably married to a set level of intelligence.
I know that you know that I know …
It does seem self-awareness, or sentience, is an emergent property of intelligence.[vi] In other words, as an animal increases in intelligence, at some point it will become aware of its own existence. This is more than simply being able to experience pleasure or pain, but the ability to experience life subjectively.
Objects found with the remains of H. floresiensis strongly suggests they made stone-age level weapons and tools.[vii] Obviously, such complex toolmaking suggests an active intelligence capable of learning new skills and – as importantly – passing those skills on to the next generation. This in turn suggests H. floresiensis possessed a language; if not a spoken language such as ours, with a huge vocabulary and complex rules of grammar, then at least some way to transmit a limited amount of information effectively and efficiently.
Evidence also exists that H. floresiensis hunted and scavenged animals such as the dwarf stegodon, a kind of elephant. To be clear, a dwarf elephant could still grow to more than two metres in height. For something the size of H. floresiensis to hunt stegodon strongly suggests they hunted in groups, which in turn strongly suggests their language was something more than a series of grunts.
With H. naledi, we are on somewhat less firm ground. Although they were larger-brained hominins than H. floresiensis, the remains of at least 15 individuals from the Rising Star Cave in South Africa were discovered without any tools or evidence of tool making. However, the species possessed a hand not dissimilar to our own, and would probably have been capable of tool-making. It is hard to imagine a hominin species living in Africa in this period, between 236,000 and 335,000 years ago, and not picking up the skill from one of the other hominin species occupying southern Africa at the same time (including, quite possibly, our own).
The Rising Star Cave in South Africa, where the fossils of several Homo naledi were discovered in the Dinaledi Chamber. H. naledi almost certainly would have needed fire – and a great deal of determination – to find their way to the chamber from its entrance. Courtesy of Creative Commons.
Furthermore, palaeoanthropologist Lee Berger, who led the expedition to recover the H. naledi remains from the Rising Star Cave, believes bodies were intentionally and repeatedly deposited there. This implies two things: first, ritual behaviour on the part of the species, and second, that they were capable of making fire, since the chamber the bones were discovered in is at the end of a long, dark, dangerous and narrow route.[viii]
I may not know much about art, but …
In his influential work on human development, The Ascent of Man, Jacob Bronowski wrote, ‘Man is not the most majestic of creatures. Long before the mammals even, the dinosaurs were far more splendid. But he has what no other animal possesses, a jig-saw of faculties which alone, over three thousand million years of life, make him creative. Every animal leaves traces of what it was; man alone leaves traces of what he created.’[ix]
Whether or not Bronowski used the term man to mean, specifically, H. sapiens, or more broadly to mean humans in general, we know that our cousins left behind more than traces of what they created. We have hundreds of stone tools, the tailings and debris of stone-tool manufacturing, and even examples of art.
I would suggest this equates to culture.
But what if there are no physical signs of culture, does it mean culture does not exist? It is often fallacious to argue that absence of evidence is not evidence of absence, but in cultural endeavours such as language or dance, there can be no evidence before the invention of writing and art.
Vervet on the lookout for predators. Photo: Simon Brown.
Simple language can be identified in many primates. Vervet monkeys, for example, have distinct calls for each of their four main predators: pythons, baboons, leopards and eagles. But we will probably never know which human species was the first to communicate with what we would describe as a complex language, one capable of conveying abstract thought. Vervet monkeys may be able to tell their fellows that a leopard is approaching, but they cannot say the leopard is hiding behind that bush or over that hill, let alone discuss the rights and wrongs of predation.
We see culture operating among our more social hominid cousins, the chimps and gorillas. Long-term field studies suggest, for example, that cultural variation exists among different chimpanzee groups, including differences in grooming, courtship and tool usage.[x] It is the ‘combined repertoire’ of chimp behaviours that is significant, demonstrating a range of cultural behaviours, a diversity that once was attributed only to our own species.
It is with the application and development of tool usage that the first signs of a distinct ‘human’ culture are found in palaeoanthropology. Whereas chimps and some bird species, like humans, use tools made from plants to gather food or built shelter, humans are the first animals to make stone tools, improving on the original material through knapping. Later, humans combined stone with other material, such as wooden handles, to improve their effectiveness; in other words using tools to make better tools. Indeed, the making of stone tools was once considered the boundary marker between members of Homo and earlier genera. Since then, the boundary for stone-tool making has been pushed well beyond those species traditionally grouped under our own genus.
Oldowan stone age tools. Courtesy of Wikimedia Commons. Photographer: Didier Descouens.
The oldest crafted stone tools found so far are from Lomekwi in Kenya, dating back 3.3 mya[xi]. First discovered in 2011, they were probably made by a species belonging to either the Australopithecus or the Kenyanthropus genera. The tools were found in an area where Kenyanthropus platyops fossils had been found earlier.
But we have to wait more than 700,000 years before there is clear evidence of stone-tool making on a large scale, something we’ll cover in detail in a later post.
Eventually some hominins were not simply making stone tools: ‘The people who made the hand axes clearly had a specific shape in mind, and often went far beyond a purely utilitarian form in the care with which they produced them.’[xii] This is an example of humans crafting tools for aesthetic appeal, not just knapping to produce a sharp edge or a convenient grip.
Earliest example of art was created by Homo erectus 500,000 years ago. Courtesy of Creative Commons. Photographer unknown.
It is with H. erectus we find the first real example of an attempt at making what we would now call ‘art’. In 2014, scientists from Netherland’s Leiden University announced the discovery of a sea shell that had been engraved with a zigzag pattern 500,000 years ago, something identified by ANU scientist Dr Stephen Munro (who did his PhD under Colin Groves!). The shell was originally collected with others at the end of the 19th century by Eugène Dubois – the discoverer of H. erectus in Java – but had not been closely examined since the 1930s. The scientists demonstrated that not only was the engraving not the result of natural forces, but that the pattern was made by ‘a strong and skillful tool-maker’[xiii]. The new date pushed back the first evidence for art by 400,000 years.
With language we’re on much shakier ground. Research suggests the physiological requirements for language exist in at least some monkeys. The stumbling block seems to arise in the way the brain is wired[xiv].
Nonetheless, as noted above with vervet monkeys, a language with a basic vocabulary exists among many primate species. It has even been shown that different species of monkey may understand some of each other’s vocabulary[xv]. Some species have even developed a basic grammar[xvi].
Extensive work has been done on language among the great apes, both in the wild and under controlled conditions. For example, the remarkable success scientists have had teaching American Sign Language to Washoe, a chimpanzee, and Koko, a lowland gorilla, demonstrate their capacity to learn quite complex vocabulary, often using it to express emotions such as sadness.
Koko, a western lowland gorilla, with her pet cat All Ball. Courtesy of Creative Commons. Photographer unknown.
But even the most optimistic view of these experiments shows that non-human great apes never demonstrate a level of intelligence found in a three-year old human child. No chimpanzee or gorilla, for example, has ever used their acquired vocabulary to ask a question.[xvii]
There is genetic evidence to suggest that the development of the capacity for language accelerated in humans after we split from the chimpanzees some seven to eight million years ago[xviii], but precisely when humans started speaking in a way that we would describe as ‘human’ is unknown; it may never be known. As with so many things in evolution, the development of a complex language capable of expressing abstract thoughts almost certainly occurred along a spectrum.
Between them, language and craft handed humans a huge advantage in the evolutionary stakes. Making stone tools, for example, minimised our weaknesses, knives and hammers allowing us to make up for a lack of sharp claws and fangs. Later, bows and throwing spears made up for our lack of speed in the chase.
Language allowed us to magnify our strengths, especially the ability to learn new things and pass that learning on to succeeding generations.
Language, and culture generally, seems to be something we share with other members of our genus, and indeed, as they are presently classified, earlier genera.
In the next post we’ll talk about bipedalism and one of the most controversial of hominin species – H. ergaster.
[i] Specifically, larger on average than the modern human brain, although the brains of archaic H. sapiens were in fact comparable to H. neanderthalensis. The following excerpt is from here.
‘To measure fossil brain volume, anthropologists have traditionally filled skulls with beads or seeds, and dumped the contents into a graduated cylinder (a precise measuring cup). They’ve also submerged molds of skulls into water, measuring the volume displaced. Today CT (computed tomography) scanning methods offer more accurate (and less-messy) measurements, but much of the data in textbooks and other references was collected the old fashioned way.
‘Based on these values, we can confidently say fossil Neanderthals and modern humans from the same time period had similar brain sizes. Twenty-three Neanderthal skulls, dating between 40,000 and 130,000 years ago, had endocranial volumes between 1172 to 1740 cm3. A sample of 60 Stone Age Homo sapiens ranged from 1090 to 1775 cm3.’
[xvii] Some scientists argue that Koko’s language skills were a result of ‘operant conditioning’, whereas others state she was indeed capable of simple questions. See Wikipedia entry here for more information and references.
Most of us did some biology at school, and most of us came out with the idea that species are groups of populations that cannot interbreed. When we’re reminded of mules, which are the offspring of horses and donkeys, we think ‘Ah, but they are sterile, aren’t they?’ Almost invariably, although there have been a few cases of fertile mules, but when cattle and bison interbreed, while the male offspring are sterile, the female offspring are fertile. All the big cats can also mate with each other, producing hybrids (where the female is fertile), and in the case of the leopon, the hybrid between a leopard and a lion, even the male might be fertile.
A tigon: hybrid from tiger father and lion mother. Because it’s a male, it would be infertile. Courtesy of Creative Commons. Photographer unknown.
Now that we can trace the ancestries not only of individual people, but whole populations and whole species, through DNA, it turns out that there has been a whole lot of successful – that is, fertile – interspecies breeding in the past. And it sometimes turns out that different species even today may interbreed with their neighbours on the quiet. For example, the primatologist Kate Detwiler discovered that two species of small monkeys in Tanzania’s Gombe National Park, the red-tailed monkey (Cercopithecus ascanius) and the blue monkey (Cercopithecus mitis), are found living in separate troops in some of the forested valleys, but in other valleys interbreed – in fact, in one or two valleys the monkey population consists entirely of hybrids.[i]
The idea that different species don’t interbreed is simply not true. They may not do so usually – but that is another thing entirely. We cannot use non-interbreeding as a criterion for species.
How then, can we define species?
George Gaylord Simpson. Courtesy of Creative Commons. Photographer unknown.
For over 150 years now, the basic guiding principle of biology has been evolution – so the question we should be asking is what is the evolutionary status of species? The palaeontologist George Gaylord Simpson (1902-1984) suggested in 1961 that the essence of species is that they are evolutionary lineages. He got little reaction at the time because his colleagues largely were hung up on the non-interbreeding criterion, but from the late 1990s his insight has been more and more appreciated. The best way to recognise an evolutionary lineage is, quite simply, that it differs from other evolutionary lineages. Horses and donkeys differ consistently and therefore represent two separate evolutionary lineages, and are therefore two different species. Similarly, blue monkeys and red-tailed monkeys differ consistently and therefore constitute separate evolutionary lineages, and again represent two different species.
Stumptailed macaque. Courtesy of Creative Commons. Photographer unknown.
If there are whole populations which consist of hybrids between two species, then what? Sometimes hybrid populations remain isolated for a good length of time and become homogeneous – and a new species is born. At least one species of monkey, the stumptailed macaque (Macaca arctoides) of mainland Southeast Asia, is thought to have arisen about 1 million years ago from a hybrid population between two other species.[ii]
For a more detailed discussion about the arguments about how to define species, especially the contest between the Biological Species Concept and the Phylogenetic Species Concept, go here.
So … generally speaking, what are genera?
So what about genera, families and other taxa?
While the taxa at both ends of the ranking are pretty straight forward – ‘species’ is eminently useful, and ‘domain’ and ‘kingdom’ are irresistibly sensible – all the ranks in between can get awfully confusing. And they are actually rather arbitrary. When, for example, do we know that a group of organisms constitute a genus rather than a family?[iii]
One simple solution would be to organise those in-between ranks chronologically. In other words, the order Primates would include all those monkey, ape and human-like species which existed from the Palaeocene epoch, and the family Bovidae would include all those antelope, buffalo and cattle, and sheep and goat species which existed from the early Miocene epoch.
This is an idea first forcefully proposed by German biologist Willi Hennig (1913-1976), considered the founder of cladistics – or ‘phylogenetic systematics’ if your thesaurus is turned on.
Willi Hennig. Courtesy of Creative Commons. Photographer unknown.
In 1966, Hennig proposed linking the taxonomic rank of a clade to its time of origin. He argued that if taxa are to mean anything they must represent monophyla – that everything in that group must be descended from a common ancestor. He also argued that taxa had to be characterised chronologically.
Hennig was an entomologist and realised while many genera of insects separated from one another tens of millions of years ago, the genera of mammals and the genera of birds separated more recently.
The idea was taken up by American scientist Morris Goodman (1925-2010), one of the founders of molecular genetics. He set about constructing a consistent scheme for the group of mammals about which he was most familiar – the primates. In 1997, he suggested that a reasonable time depth for a primate genus would be seven million years, partly because this would do the least violence to the presently accepted system of determining genera.
Colin surveyed many of the mammalian genera that taxonomists had recognised and found that most had separated from each other less than seven million years ago. Subsequently, he proposed that five million years was a more appropriate time depth for mammalian genera: the Miocene-Pliocene boundary.
Furthermore, Colin suggested that the taxonomic rank of ‘family’ had a time depth of 24 million years, separate families splitting around the time of the Oligocene-Miocene boundary. Going up one more ranking, the different ‘orders’ separated around the time of the Cretaceous-Tertiary boundary (the famous K-T boundary that marks the arrival of the asteroid that wiped out non-avian dinosaurs[v]).
Colin Groves. Photo: Simon Brown.
One of the consequences of Goodman’s proposals for palaeoanthropology is that most if not all members of the human lineage would belong to a single genus. Indeed, using his original suggested time depth of seven million years, Goodman even included chimpanzees into Homo. Overall, the later modifications devised by Colin play less havoc with the established order, but they would still require that most human fossils be placed in the same genus as ourselves.
Arguments about when hominins evolved into a genus that can be described as wholly human traditionally revolved around the relative importance of different physical characteristics: brain size, dentition, general morphology (body size, especially the extent of sexual dimorphism), and primary form of locomotion.
Other more controversial factors sometimes taken into consideration include tool-making, art and other signs of culture, and evidence of community living.
For example, some experts such as Ian Tattersall, curator emeritus with New York’s American Museum of Natural History, argue that the cranium of Homo floresiensis (the Hobbit, see here, here and here) is too archaic for it to be included in our genus.
This leads us to our second, and more controversial opinion: following Colin’s plan our genus would include not only H. floresiensis but even older and more archaically featured species traditionally belonging to other genera, such as the Australopithecines, for example, which include the Taung Child and Mrs Ples.
Colin argued that the Miocene-Pliocene boundary more or less corresponds to the onset of the only characteristic definitely belonging solely to our genus and to no other genera among the great apes – bipedalism. By bipedalism we mean that the main form of locomotion is walking or running on two legs, with the big toe aligned with the other toes in the foot.[vi]
Accepting this argument has two major implications and several minor ones for palaeoanthropology. First, and least controversially, brain size is not by itself a qualification for membership of the human genus. Specifically, a small brain does not exclude membership.
Homo naledi. Courtesy of Creative Commons. Photographer unknown.
The discovery of H. floresiensis and H. naledi in the 21st century, with an average brain size of around 420 cm3 (about the size of a modern chimpanzee) and 500 cm3 respectively, clearly demonstrates that many humans were small brained compared to H. sapiens but possibly still capable of sophisticated tool-making and ritual behaviour.
Secondly, accepting a time criterion in determining what species do and do not belong to the genus Homo means that strictly morphological traits are no longer intrinsic in determining human status.
In the next post, we’ll look in more detail at brain size, culture and bipedalism as criteria for determining whether or not a species is human.
[iii] Sigwart, J., Sutton, M. D., & Bennett, K. (2017). ‘How big is a genus? Towards a nomothetic systematics’. Zoological Journal of the Linnean Society. https://doi.org/10.1093/zoolinnean/zlx059
[iv] Groves, Colin. ‘Time and taxonomy’. Ludus Vitalis. Vol IX. No 15. 2001.
& Groves, Colin. ‘Speciation in hominin evolution’. African Genesis: Perspectives on Hominin Evolution. Ed Reynolds, Sally & Gallagher, Andrew. Cambridge University Press. 2012.
& Groves, Colin. ‘Current taxonomy and diversity of crown ruminants above the species level’. Zitteliana B32, International Conference on Ruminant Phylogenetics, ed. Prof. Dr G Worheide, Bavarian State Collection for Paleontology and Geology, Munich.
[v] Now also sometimes referred to as the Cretaceous-Palaeogene (K-Pg) boundary.
‘Burdalone’ is an old Scottish word meaning the last bird in the nest, the one left when all the other chicks have flown or all the other chicks have died. It’s a sad and lonely word, and perfectly describes Homo sapiens.
When one of the first members of our own species studied the world around her, most of what she saw would be familiar to us today, whether from personal experience or from watching nature documentaries about Africa. Extensive grasslands dotted with acacias, watering holes and narrow rivers with crumbling banks, herds of large grazing animals such as wildebeest and zebra, black herons and lizards, secretarybirds and crocodiles, a lion pride or two, and our deadliest predators – a leopard and a pack of hyenas.
The south African Highveld, the kind of savannah our ancestors evolved in over four million years ago. Photo: Simon Brown.
What she also saw, and which none of us will ever see, is other groups of human beings that were not H. sapiens. Like our ancestor, they were striding on two legs and using their large brains and opposable thumbs to harvest nuts and berries, sometimes to hunt or scavenge for meat, and to fend off predators. They looked very similar to us, used tools, and some may even have created art and used language to talk to one another.
Around 350,000 years ago, at this stage the earliest date we know H.sapiens might have first strode the planet[i], there was no reason to think things would ever change.
But to say that we are human today is to say that we are members of a single worldwide species. This is extraordinary because for millions of years to be human meant that you could be a member of any one of a number of different but related species.
It should not be contentious to say that all members of the genus Homo are human – after all, this is what the Latin word ‘homo’ means – but it is contentious to suggest, as I will later in these posts, that all bipedal great apes are human.
But first it’s important to state that it’s currently impossible, and may forever be impossible, to finally determine when we stopped simply being hominids – that is, all the apes except for the gibbon – and became hominins as well – that branch of the hominids exclusive to us and our human cousins; this is the point at which chimpanzees went their way and we went ours.[ii] We may never know exactly when the thousands of physical and psychological characteristics that distinguish us from other great apes evolved; what we can be sure about is that almost of them were shared with at least some of our hominin ancestors.
We are so close to our cousins, genetically and historically, that making a distinction between whether or not they are human seems farcical. Indeed, the same argument can be made for any two species close to each other in the hominin line.
In 2005, British celebrity Alan Titchmarsh allowed professional make-up artists to disguise him as a Neanderthal; he then walked along the streets of London, almost completely ignored by everyone.[iii]
Homo sapiens or H. neanderthalensis? Courtesy of Creative Commons. Photographer unknown.
At some point we need to demarcate between those species we consider human and those we consider pre-human, and to date the only specific marker that distinguishes all of us from all of them is bipedalism, not some arbitrarily determined measurement of brain capacity, morphology or dentition.
As well, research into the workings of the human brain, and into animal intelligence generally, has thrown into doubt those psychological characteristics we traditionally considered to be peculiarly human, characteristics that made us special and put us above the rest of the animal kingdom. Once upon a time, we were considered the only animal to make tools, then the only animal to make tools and smile, then the only animal to make tools, smile and do handstands.
It’s similar to a town building a bridge and claiming it’s the only bridge in the world, only to discover that a nearby town has one as well. So the first town now claims it’s the only single-span bridge in the world, until it learns there is a another single-span bridge in the next county. The first town now claims it is the only single-span bridge in the world with green arches, and so on, every new definition increasingly trivialising what makes its bridge special.
There is strong evidence that intelligence has arisen many times in the animal kingdom: in primates, cetaceans, elephants, larger carnivores such as dogs, hyenas and the big cats; birds, particularly corvids and parrots; and some molluscs such as octopuses and possibly squids.
There is also growing evidence that self-awareness and even a theory-of-mind[iv] exists in other primates such as chimpanzees and some birds such as crows.
There is growing evidence that animals other than humans, such as chimpanzees, have a Theory of Mind. Courtesy of Creative Commons. Photographer unknown.
So what are the characteristics that separate humans from our nearest living relatives, the chimpanzee and bonobo?
Before we answer that, we have to talk taxonomy and cladistics – how scientists classify living things.
Life is a spectrum
In his book The Vital Question, biochemist Nick Lane writes that ‘the distinction between a “living planet” – one that is geologically active – and a living cell is only a matter of definition … Here is a living planet giving rise to life, and the two can’t be separated without splitting a continuum.’[v]
Different scientists may employ different markers or waypoints in determining the start of life on Earth, all of which are subject to controversy and disagreement, but the truth is that there is no precise point in time when anyone could claim that a given chemical process for the first time was created by life rather than geology; it would be an arbitrary decision.
The same principle applies throughout evolution. There is no precise point in time where we can say fish gave rise to amphibians or basal reptiles to dinosaurs.
Changes in life brought about by evolution through natural selection isn’t episodic, it’s a spectrum.
But evolution does present a handful of events when with some certainty we can say a new direction had begun – a direction with significant ramifications for all life that follows.
The first of these, and covered in some detail in The Vital Question, concerns the creation of the eukaryotic cell: a morphologically complex cell that contains a separate nucleus and mitochondria, each surrounded by a double membrane. As far as we know this remarkable event occurred only once in all history[vi]. An archaeon, a single-celled prokaryote, absorbed another kind of prokaryote – a bacteria – and instead of consuming it established a symbiotic relationship.
The eukaryotic cell – morphological complexity derived from the synthesis of two prokaryotes, an archaeon and a bacterium. After the creation of life itself, this synthesis is perhaps the most significant event in the history of our planet. Courtesy of Creative Commons.
At some point later in history, some of the descendants of that first complex cell started a symbiotic relationship with a second prokaryote invader, creating chloroplasts and starting the line that would eventually lead to plants and green algae.
More recently, the arrival of the first human was an event with tremendous ramifications for all life on earth.
But when did this happen?
The king of Spain did what?
Before we go any further, we need to talk about a subject that normally works like a sedative on anyone not interested in taxonomic detail: the organisation of the taxa themselves.
I promise to keep this short and to the point, but it’s important to cover because we need to reconsider how and where our human family fits in with other living thing. And, of course, when it all happened.
Mnemonics are as much a part of school science classes as microscopes and Bunsen burners. For example, one mnemonic frequently used in the last century for memorising the different taxonomic ranks was ‘King Philip Came Over From Great Spain’, a mnemonic for the main taxa in the Linnaean system:
Courtesy of Creative Commons.
Kingdom,
Phylum,
Class,
Order,
Family,
Genus, and
Species.
Taxonomic ranking has been around for as long as humans have been curious about the natural world, but the above ranking developed from a system introduced by the Swedish naturalist Carl Linnaeus in the 18th century. He wanted to organise living things so their biological relationship to each other was made very clear. He did this by using shared characteristics to lump things together.
For example, these days all animals with fur, warm blood and that suckle their young with milk are put into one group, the class called mammals. The mammals themselves are grouped together with all animals with a backbone to form a phylum called the chordates. The chordates and animals without a backbone are thrown together into a kingdom called Animalia. More formally, taxa – the collective noun for the rankings – sharing a more recent common ancestor are more closely related than they are to taxa which share a more remote common ancestor: in other words a wombat is more closely related to a dog than it is to a crocodile, and more closely related to a crocodile than it is to a flatworm.
Linnaean taxonomy also introduced the binomial, the familiar two-name identifier used in science to classify an organism at the most detailed commonly used level, that of species. Homo sapiens, for example, is the binomial for human beings, just as Panthera leo is the binomial for lions and Quercus robur is the binomial for the English oak. The first word is the genus (plural genera), the second the species.
Taxonomy is a lovely idea, and appeals to anyone who thinks good old common sense is all you need when sorting bookshelves and tidying kitchen cupboards. For over two hundred years it was regarded as an almost fool-proof system: a place for every living thing and every living thing in its place.
But our knowledge of the natural world is not like that of our kitchen. Like the natural world itself, it is messy, chaotic, growing and constantly evolving.
In 1990, American microbiologist Carl Woese (1928-2012) suggested a new step was needed at the top of the taxonomic ladder to reflect the discovery of a whole branch of life whose existence was never suspected until the 1970s. The archaea, single-celled prokaryotes, were long thought to be a kind of bacteria, but work by Woese and other scientists revealed they are as chemically different from bacteria as we are.
The commonly accepted taxonomic ranks now start with ‘domain’, leaving us with cumbersome and self-defeating mnemonics such as ‘Determined, Kind People Can Often Follow Ghostly Screams’ or ‘Do Kings Prefer Chess On Fridays, Generally Speaking’.
Domain isn’t the only extra rank added over the decades. We also have ‘subfamily’, ‘tribe’, and sometimes ‘subtribe’, ‘subgenus’ and ‘subspecies’, and that’s just in the field of zoology.
In the story of ‘Us’ we’ll be dealing mainly with genus and species, and in the next post we’ll discuss what makes up both taxa.
[ii] Some palaeoanthropologists include chimps and bonobos in the hominin. Rather than outlining all the arguments for or against, I’ll err on the side of caution and include only our immediate family in the hominins.
[iv] This is the ability to attribute mental states similar to your own to other members of at least your own species and possibly other species as well.
[v] Lane, Nick; The Vital Question; London, 2015; p 27.
[vi] This may have happened a second time. A single-celled organism with a nucleus, and possibly mitochondria, dubbed Parakaryon myojinensis, was retrieved a few years ago from the foot of a sea creature found off a coral atoll not far from Japan.
The main difference between P. myojinensis and all other eukaryotes is that its nucleus and mitochondria are surrounded by a single membrane instead of a double one, and its DNA is stored in filaments (as in bacteria) suggesting it is the result of a different line of evolution from all other eukaryotes. Indeed, there is some argument as to whether it is a true eukaryote at all. The only thing that can be said with some certainty is that it is definitely not a prokaryote.
No other example of this creature, or anything similar, has since been recovered. Nonetheless, when it comes to science, hope springs eternal …
This and the following five posts will be about Us. Not Uncle Sam or Ultra Sound or Ultimate Spas. Not you and me. But all of Us. Every single human alive today and every single human who has existed in the past. And by every human I mean every member of the genus Homo, and every member of the genera Australopithecus, Kenyanthropus and Paranthropus, a lineage that stretches back nearly five million years in the past and is still going strong today.
I considered another title for this series of posts – ‘Mongrel’ – because Homo sapiens are mongrels. I don’t mean in the way an Australian might call you a ‘mongrel’ if you rear-end his ute or support a different footie team, but in the sense that we are animals of mixed breeding.
Colin Grove. Photo: Simon Brown
I want to write about the revelation made by palaeoanthropology over the last 25 or so years that Anatomically Modern Humans (AMH) have no single direct ancestor. The different species that gave rise to us bred with each other again and again, cross-pollinating over millions of years. We are, each and every one of us a mulatto, a crossbreed, a cafuzo, a zambo … in short, a mongrel. This is something for us to crow about. We are the beneficiaries of millions of years of striving, surviving and thriving by many other members of our hominin tribe. Having said that, recognising that we owe our existence to a plethora of species and not to one single predestined or divinely sanctioned line of descent, may also help us shed our belief in the exceptionalism of H. sapiens.
These posts are also a way for me to record a project I long dreamt of doing and eventually started some six years ago but can no longer complete, a book about hominin evolution I was writing with my friend, the late Colin Groves[i]. I cannot write that book without Colin – his knowledge and experience were unique even in the rather rarefied circle of palaeoanthropology – but what I can do is finally record as faithfully as possible some of his ideas about hominin evolution.
To start with, I’d like you to meet a small child. A child named Taung.
Darwin was right
The child first came to attention in 1924 when it’s tiny skull was discovered by Raymond Dart in one of two boxes of tufa and sandstone debris he received as he was dressing to attend a wedding as best man.
Dart, an Australian doctor and anatomist, had only recently taken up the post of professor at the University of Witwatersrand in Johannesburg, and had spread the word he was interested in any fossils his students or acquaintances might uncover to help stock his fledgling laboratory. In this case, the debris was from a limestone quarry in Taung, a small mining town in South Africa’s Northwest Province.
When the boxes arrived he hurriedly inspected them. In the second box he saw something that changed his life and the history of palaeoanthropology.
In his own words, a thrill of excitement shot through him.
‘On the very top of the rock heap was what was undoubtedly an endocranial cast or mold of the interior of the skull. Had it been only the fossilised brain cast of any species of ape it would have ranked as a great discovery, for such a thing had never before been reported … a brain three times as large as that of a baboon and considerably bigger than that of an adult chimpanzee …
Cast of Taung child. Photo: Simon Brown
‘But was there anywhere among this pile of rocks, a face to fit the brain? I ransacked feverishly through the boxes. My search was rewarded, for I found a large stone with a depression into which the cast fitted perfectly … Here I was certain was one of the most significant finds ever made in the history of anthropology.
‘Darwin’s largely discredited theory that man’s early progenitors probably lived in Africa came back to me.’[ii]
Indeed, Dart’s discovery eventually switched the focus of palaeoanthropology’s search for the origin of our species from Eurasia to Africa, an origin Charles Darwin had predicted in The Descent of Man in 1871.
Using his wife’s knitting needles, it took Dart weeks to separate the Taung Child (Taung 1) from its breccia matrix. The paper[iii] he wrote about the discovery appeared in Nature in early 1925, and in that paper he named the specimen Australopithecus africanus, Africa’s southern ape.
Raymond Dart with the skull of the Taung child. Courtesy of Creative Commons. Photographer unknown.
At first, the scientific establishment reacted negatively to Dart’s hypothesis that the Taung Child represented an ancestor of modern humans. Heretofore it had been believed humans must have evolved in Europe or Asia, a belief reinforced with the discovery of H. neanderthalensis in 1829 (but not recognised as a different species from us until 1856) and H. erectus in Java in 1891 (a story we’ll come back to later in this series of posts).
Over the following decades, however, the number and diversity of fossils uncovered in southern and eastern Africa have overwhelmingly supported the ‘Out of Africa’ hypothesis for human origins.[iv]
The Taung Child itself was thought to be about three years old when it died. Not only was its life short, it ended violently. In 2006, the University of Witwatersrand’s Lee Berger wrote that marks in the Taung Child’s eye sockets and on its skull suggested it was probably killed by a large bird of prey.[v]
Even though it was the first described member of the genus, it turned out A. africanus was not its oldest member, and may not even have been one of our direct ancestors.
Meet the great-great-great-grandparents
At the risk of making a bad rhyme, exactly what does it mean to be an Australopithecine?
This is a matter of debate. Some scientists merge a chronologically older primate genus, Ardipithecus, with Australopithecus, to make the subtribe Australopithecina. Others leave out Ardipithecus, and include Paranthropus and Kenyanthropus with the Australopithecines. While they’re at it, some scientists consider Australopithecines to be a member of the human family, while others think the family starts much later – with the first species in the genus Homo.
It gets very confusing very fast, especially since every new discovery – and over the last 25 years there have been many of those – seems to generate a new species and subsequently a new debate of what it means to be human, hominin, or hominini (generally accepted to be humans plus chimpanzees). Or for that matter, what should be included in the genera Australopithecus, Homo, Paranthropus and so on and so forth.
For the sake of these posts, I’m assuming at this point that Australopithecines are fine and upstanding members of our human family. Great-great-great-grandparents (or cousins to the nth degree), in a manner of speaking. At a later point I’ll be examining more deeply what makes a genus … but we’ll paddle that delta when we get to it.
Australopithecus anamensis: the first human? Courtesy of Creative Commons. Photographer unknown.
The oldest species belonging to this genus is A.anamensis[vi], kicking off just over four million years ago (mya). Other Australopithecines include A. garhi, A. afarensis (Lucy is probably the most famous example of this species, if not the most famous human fossil of all), A. bahrelghazali, A. deyiremeda, A. prometheus and A. sediba. A. sediba is the last known of the genus as well as the most recently discovered[vii], existing as recently as 1.8 mya, making it a contemporary of one of our ancestors, H. ergaster.
Over the two million plus years the genus existed, cranial capacity jumped from around the 360cc mark (slightly smaller than the average for a chimpanzee) to nearly 440cc, an increase of over 20%.
The Australopithecines are generally thought to have given rise to our genus around 2.4 mya. Occasionally one Australopithecine or another is nominated as materfamilias, but the truth is no one really knows which species – if any of those so far discovered – gave rise to our side of the family. As well, there is constant toing and froing about how many species there actually are (and as we’ll see the same toing and froing goes on in discussions about the members of our own genus).
In the next post I’ll discuss what lays at the heart of all of these debates: the big question, a question that may never be satisfactorily answered.
[iv] Including the discovery of Mrs Ples (STS 5) in 1947 by Robert Broom and John T. Robinson, an almost complete skull of A. africanus. (For more on Mrs Ples, see my earlier blog here.)
Last weekend, AJ and I went camping at Pilanesberg National Park. Well, I say camping. Our tent had a refrigerator in it. And a kettle. And power points for our mobile phones.
Extraordinarily rough camping conditions prevailed at Pilanesberg.
Anyway, together with some fellow teachers from AJ’s school we went comfortably camping at a park famous for providing visitors the opportunity to catch sight of the Big Five: Cape buffalo, elephants, leopards, lions and rhinos.
While we did manage to see a line of lying lions in the distance – we needed binoculars to find them – for the most part the Big Five managed to elude us.
This is probably because AJ and I decided to forgo the chance of getting up before sunrise and braving subzero temperatures to tour the park in an open truck. Those who did make the effort not only managed to see the Big Five but cheetahs as well. However, they were cold. Very cold. Their fingers snapped off trying to focus their Nikon 70-300 zoom lenses.
We, on the other hand, got up at a civil hour, had a hot breakfast, and entered the park about 9.30 am, courtesy of the generous school librarian and his huge red ute. Although most of the predators and large herbivores had by then decided to migrate to warmer climes, we did see plenty of impressive wildlife, including kudus, wildebeest, zebras and giraffes.
Grey heron.
And our fingers didn’t drop off focusing our zoom lens. Not just because it was warmer, but because our camera decided to stop working, forcing us to rely on the cameras on our mobile phones.
In fact, we didn’t really have to leave our tent to see some very impressive locals. Our camping site had been colonised by a several groups of impala, vervet monkeys, chacma baboons, banded mongooses, hornbills and helmeted guinea fowls.
The impala were the most impressive of all. They’re magnificently streamlined antelopes with a colour scheme designed by an Italian fashion house. The males sport magnificent horns shaped like ancient Greek lyres. The effect is somewhat spoiled when the males start practicing for the rutting season by pretending to come to blows and blowing through their noses, sounding like a parcel of agitated pigs with head colds.
Impala cleaning his nose in preparation for a good snort.
The funniest sight is watching the normally docile guinea fowls suddenly scatter, running one way and then the other. AJ said the bird reminded her of a fusty old women from the 19th century picking up her skirts and pelting down the street.
The vervets spend most of their time high in trees or sitting like sandstone statues on the roof line of the campsite’s restaurant. They look down on their fellow primates with aloof disinterest.
Vervet practising aloofness.
One of the highlights of the expedition was totally unexpected. We came across the ruins of an iron age kraal not far from the park’s entrance. The area’s fenced off, and if the main gate’s red light is flashing – meaning something like a lion or leopard or elephant is also touring the ruins – you’re advised to stay out. On this occasion we were the only visitors.
The kraal was built by the Tswana chief Pilane, hence the name of the park. The ruins are well signed, giving a brief history of the kraal and what the various buildings and spaces were used for. The kraal’s main lookout provided wonderful views of the park. It reminded AJ and me of some of the ancient hill forts on the border of Wales and England we visited in 2010. Although those hill forts weren’t surrounded by thorn trees. I managed to get one long branch wrapped around my left leg. It took some doing to disentangle myself, and the small wounds made by the thorns itched for hours afterwards.
Warning outside the iron age kraal.
The kraal itself!
View from the kraal lookout.
Thornbush.
A second highlight was the visitor’s centre, where people can eat and drink on a wide deck overlooking the bush. A large salt lick is placed not far from the deck, drawing giraffes, zebra and wildebeest, although when we were there only one giraffe, the biggest, got to enjoy the lick. He’d tolerate other giraffes having a go, but didn’t hesitate kicking any wildebeest who came for their turn. The zebras were pluckier than the wildebeest, but no more successful.
A giraffe. Not a zebra or wildebeest.
The landscape between Johannesburg and Pilanesberg is eerily familiar. Geographically and botanically it’s very similar to the Southern Tablelands, especially the stretch between Canberra and Yass. It’s not surprising, I suppose: South Africa and Australia were once joined at the hip. The soft landscape is covered in grasses and acacias and other plants adapted to a hot, dry climate. True, South Africa has lions while Australia has sheep, and South African kopjes are rockier than Australian hills, but nonetheless …
The similarity even extends to bushfires. Pilanesberg hosted its own bushfire the week before we arrived, and large parts of the park were black and ash grey, again strangely familiar to anyone from inland New South Wales.
Bushfire damage.
It’s not like AJ and I are looking for similarities, but perhaps a little homesickness makes you look for them instead of the differences.
In October, we hope to make our way southeast to Durban for a few days, stopping over at the Drakensberg on the way.
Until recently, only seven species made up the group of primates known as the great apes, or Hominidae. Two orangutan species (Sumatran and Bornean), two gorilla species (eastern and western), two chimpanzee species (chimpanzees and bonobos), and us.
But in a report recently published in Current Biology, an international team of scientists announced a new hominid with fewer than 800 members, Pongo tapanuliensis, found just south of Lake Toba in Sumatra. To save your tongue twisting around that particular binomen, we can call it the Tapanuli orangutan.
The scientists compared skull, jaw and dental characteristics of a Tapanuli specimen with those of the Sumatran and Bornean species, and analysed 37 orangutan genomes as a second line of evidence.
Three species of orangutan: from left, Bornean, Sumatran, Tapanuli. Photo credits: Eric Kilby, Aiwok, Tim Laman
The report gained a great deal of media attention: not only because we humans had a new cousin, but because the Tapanuli is an endangered species.
However, there were dissenting voices. In an interview with the ABC, for example, Lee Christidis from Southern Cross University pointed out that the analysis had been carried out on only one specimen and that the DNA evidence was at best ambiguous.
It’s only fair to point out that it’s often the case that a species will be described by a single representative organism, or, as happens frequently in palaeontology, those fragments of a single organism that have been fossilised or otherwise survived over many millions of years.
The report also generated discussion about what we mean by the word ‘species’. Jerry Coyne, professor emeritus at the University of Chicago and author of the excellent Why Evolution is True, wrote in his blog:
‘Not only do I see this new “species” as merely an isolated and genetically differentiated population (as are many human populations regarded as H. sapiens), but I’d also contend that there is only one species of orangutan overall, with these three groups all being subspecies. Sadly, a lot of systematists don’t see it that way, as they seem to think that any isolated population, if it can be told apart morphologically or genetically from others, warrants being named as a new species. Yet to evolutionists, a “species” is not an arbitrary segment of nature’s continuum, but real entities that maintain their “realness” because they don’t exchange any (or many) genes with other such entities where they cohabit in nature.’
But is this indeed the definition of species with the greatest currency among most biologists?
To start with, there has to a definition that works across all fields. A primatologist cannot have a different concept of species from, say, an entomologist, or the whole point of taxonomy – the orderly classification of living things that demonstrates their evolutionary relationships – starts to fall apart.
This doesn’t mean that definitions in biology – or any scientific endeavour, for that matter – are written in stone. As our knowledge of the world around us grows, the language we use to explore, explicate and explain that knowledge must also grow.
The definition I was taught at school is not dissimilar to Coyne’s quoted above, and is based on what is called the Biological Species Concept (BSC), developed by Ernst Mayr and Theodosius Dobzhansky in the early 1960s (Coyne did some graduate work under Dobzhansky at Rockefeller University). As Colin Groves, professor emeritus at the Australian National University, wrote, ‘This concept states that under natural conditions a species ‘should not exchange genes with other species’[i]. Groves goes on to point out that ‘ … the popular idea that two species are “unable” to interbreed is a misunderstanding: it is not that they cannot interbreed, it is that they do not.‘
The BSC was further refined by Mayr and Jared Diamond in a paper on Melanesian birds in 2001, and then in 2004 by the aforementioned Jerry Coyne with H. Allen Orr in a book about speciation called, appropriately enough, Speciation.
Groves argues that the modified definition of BSC risks different standards of comparison in different taxonomic groups: it’s a definition that won’t work across different fields, in other words.
Groves again: ‘If a genus contains a pair of sympatric[ii] sibling species (species that differ only slightly, inconspicuously), the standard for species recognition will be set much “lower” than in a genus in which sympatric species pairs are grossly different. It is the search for objective standards – for an operational means of distinguishing species – that has been responsible for the controversies that marked taxonomic discussions over the past 15 or 20 years.’[iii]
Many biologists now use what is called the Phylogenetic Species Concept (PSC), developed by American biologist Joel Cracraft from the early 1980s. Put very simply, in this concept a species is the smallest population of organisms that is measurably different from other populations sharing the same ancestry. Note that this concept says nothing whatsoever about species sharing genes, such as happened between Homo sapiens and H. neanderthalensis around 100,000 years ago.
It’s important to note that both the BSC and the PSC are attempts to operationalise the evolutionary concept of species; that is, that a species is an evolutionary lineage.
While the report in Current Biology describing the Tapanuli orangutan as a new species of great ape has, for the most part, been received positively, the fact that many distinguished scientists question the findings shows that the debate about what constitutes a species is ongoing.
[i] Groves, Colin. ‘Speciation in hominin evolution’; African Genesis: Perspectives on Hominin Evolution; ed Reynolds, Sally C. & Gallagher, Andrew; Cambridge University Press; Cambridge; 2012, p 46.
[ii] Sympatry occurs when two or more species live in the same geographic area.
Corvus corax, the common raven. Photo: Pkspks [CC BY-SA 4.0]
It’s no secret that corvids – crows and ravens – are exceptionally smart for birds, especially at problem solving. Now an experiment carried out with ravens provides evidence they may have a basic Theory of Mind as well; this means they have an ability to attribute mental states they experience to another raven.
In a paper published in Nature in February, researchers Thomas Bugnyar, Stephan Reber and Cameron Buckner from the universities of Vienna and Houston, carried out an ingenious experiment that tested how ravens caching food behaved when they thought they were being seen by another raven.
There is increasing evidence that the Theory of Mind exists in chimpanzees, bonobos, scrub jays and ravens. How equivalent the experience of a ToM is between species is, so far, untestable, but the strong possibility that some form of ToM exists in different animals provides yet more evidence of the complexity of the mental life of species apart from humans.
Not only does this add weight to calls that humans should reconsider the way they relate to other animals, especially the often appalling way we treat farmed and domesticated animals, but firmly places Homo sapiens as the product of the same evolutionary process that produced ravens, dogs and garden slugs.
Strange Borders 