A chronological table of fossil finds*
Have you read the preceding page "Humans - out of Africa - the story of human evolution?"
* See also "The role of DNA and mutations in fossil identification", at /dna-and-mutations.html
The chances of any of us finishing up as a fossil, and for that matter any of our predecessors, immediate or otherwise, are vanishingly small, Bill Bryson reminds us in sober fashion: most of what has lived on Earth has left behind no fossil record at all. It has been estimated that less than one species in 10,000 has made it into the fossil record, and most of what we do have is "almost absurdly biased" in favour of marine creatures[1]. Such fossils as we do have available to us are generally in fragments, from which one endeavours to extrapolate to a whole body and then to a singular species. They are also generally spaced well apart in time not uncommonly by hundreds of thousands or even millions of years, and it is often difficult or well nigh impossible beyond educated guesswork to draw general conclusions as to lineage[2]. Such conclusions as can be drawn are frequently interpreted according to the world view or system belief of the person who discovered the fossil whose significance is under consideration, and in most instances it all boils down to a matter of interpretation - little can be said that won’t be the subject of dispute by someone else!
Some favour a linear interpretation that interprets everything as the inevitable march from one discovered species to another until it metamorphoses into our own. According to this view, we are the culmination of the evolutionary process with “each species of hominid carrying the baton of development so far, then handing it on to a younger, fresher runner”[3]. Others see a more fragmented and bushy process in which there was and is nothing inevitable about the rise of Homo sapiens to the so-called top of the tree.
In A Short History of Nearly Everything[4], Bill Bryson reviews the chronology of fossil discovery from the time of Thomas Dubois’ discovery of a Homo erectus fossil in Java in 1887 until the present which for him (Bryson) is about 2002 when he wrote the book, but much has happened since then. So let’s commence with a dispute about a number of more recent sets of fossil finds and their significance as perceived through the eyes of the eminent palaeontologists who unearthed them, each being burdened with with his or her own world view and methods of interpretation.
On the one hand, in the blue corner we have the Great Rift Valley and East Africa faction led by Louis Leakey and his son Richard who espouse Homo habilis, the famous toolmaker whom the Leakeys advanced in 1965 just over 50 years ago now, as the necessary bridge between Australopithecus and Homo, ape and man, and on the other, in the red corner we have Lee Berger and the South African faction who in the last several years (2010 and 2013) have acquired two additional strings to their bow: firstly australopithecus sediba as the necessary link, and latterly an unexpected contender from the South who even outranks sediba in qualifications, a rank outsider by the name of Homo naledi [5], explored in some detail below.
Meanwhile, on the sidelines there are other players each with their own fossil samples to advance as having significance, such as Bill Kimbel from Arizona University’s Institute of Human Origins and Sonia Harmand of Stoney Creek University. Their finds are mentioned below.
The major players, sediba, habilis and erectus, appear below as the third, fourth and fifth figures. But is this really where sediba fits in the natural order of things?
* See also "The role of DNA and mutations in fossil identification", at /dna-and-mutations.html
The chances of any of us finishing up as a fossil, and for that matter any of our predecessors, immediate or otherwise, are vanishingly small, Bill Bryson reminds us in sober fashion: most of what has lived on Earth has left behind no fossil record at all. It has been estimated that less than one species in 10,000 has made it into the fossil record, and most of what we do have is "almost absurdly biased" in favour of marine creatures[1]. Such fossils as we do have available to us are generally in fragments, from which one endeavours to extrapolate to a whole body and then to a singular species. They are also generally spaced well apart in time not uncommonly by hundreds of thousands or even millions of years, and it is often difficult or well nigh impossible beyond educated guesswork to draw general conclusions as to lineage[2]. Such conclusions as can be drawn are frequently interpreted according to the world view or system belief of the person who discovered the fossil whose significance is under consideration, and in most instances it all boils down to a matter of interpretation - little can be said that won’t be the subject of dispute by someone else!
Some favour a linear interpretation that interprets everything as the inevitable march from one discovered species to another until it metamorphoses into our own. According to this view, we are the culmination of the evolutionary process with “each species of hominid carrying the baton of development so far, then handing it on to a younger, fresher runner”[3]. Others see a more fragmented and bushy process in which there was and is nothing inevitable about the rise of Homo sapiens to the so-called top of the tree.
In A Short History of Nearly Everything[4], Bill Bryson reviews the chronology of fossil discovery from the time of Thomas Dubois’ discovery of a Homo erectus fossil in Java in 1887 until the present which for him (Bryson) is about 2002 when he wrote the book, but much has happened since then. So let’s commence with a dispute about a number of more recent sets of fossil finds and their significance as perceived through the eyes of the eminent palaeontologists who unearthed them, each being burdened with with his or her own world view and methods of interpretation.
On the one hand, in the blue corner we have the Great Rift Valley and East Africa faction led by Louis Leakey and his son Richard who espouse Homo habilis, the famous toolmaker whom the Leakeys advanced in 1965 just over 50 years ago now, as the necessary bridge between Australopithecus and Homo, ape and man, and on the other, in the red corner we have Lee Berger and the South African faction who in the last several years (2010 and 2013) have acquired two additional strings to their bow: firstly australopithecus sediba as the necessary link, and latterly an unexpected contender from the South who even outranks sediba in qualifications, a rank outsider by the name of Homo naledi [5], explored in some detail below.
Meanwhile, on the sidelines there are other players each with their own fossil samples to advance as having significance, such as Bill Kimbel from Arizona University’s Institute of Human Origins and Sonia Harmand of Stoney Creek University. Their finds are mentioned below.
The major players, sediba, habilis and erectus, appear below as the third, fourth and fifth figures. But is this really where sediba fits in the natural order of things?
Before reviewing the panorama as a whole, let's consider the intermediate candidates who are the subject of this dispute. Firstly:
Homo habilis, 2.3 Mya, found by Jonathan Leakey 1960s Olduvai Gorge, African Great Rift Valley, stone tools, varied diet
In the 1960s, in the Olduvai Gorge, a 50 km wide canyon in the Serengeti Plain in northern Tanzania that is part of the African Rift Valley, Jonathan Leakey found a hominin fossil about 1.4 metres tall, apparently of the same genus as human beings (Homo) which he therefore christened Homo habilis or ‘handy man’. This makes it the oldest species of the genus that included modern humans Homo habilis apparently had facility with the systematic manufacture and use of stone tools. Their brains were also a lot bigger than those of the australopithecines. This species was dated to around 2.3 Mya and it is thought may mark the real beginnings of human history. The use of tools made available a more varied diet, including meat, providing the metabolic energy for larger brains. It was also predominantly bipedal.
The Olduwan site was also occupied by P. boisei 1.8 million years ago, H. erectus 1.2 million years ago and H. sapiens 17,000 years ago.
Then, and perhaps on firmer ground: H. erectus (aka ergaster: African H. erectus), 1 Mya
Homo habilis lived in East Africa with several other species, including robust australopithecines (Paranthropus), and perhaps six or more different species of hominins lived at the time of habilis, but about one million years ago, various forms of homo erectus (also known as ergaster) [5.1] displaced all other forms of hominins. Homo ergaster specimens were taller than habilis, and had larger brains ranging from 850 to 1000 cc, close to the brain size in modern humans. From ca 1.5 mya, they began to manufacture a new type of stone tool with more sophistication than Oldawan tools. It is also likely that they had superior linguistic capabilities to those of habilis.
H. erectus migrations[6] This species included the first hominins to migrate out of East Africa and then out of Africa entirely into Eurasia. By about 700,000 years ago, communities of Homo erectus lived in parts of southern Asia and had even entered Ice Age Europe. Erectus remains were first found in Indonesia in 1891 and in the 1920s in the Zhoukoudian cave not too far from Beijing. It appears that erectus explored a wider variety of niches than habilis, and managed to live in regions whose climates would have been too cold or two seasonal for habilis. However, erectus did not manage to inhabit the cold heartland of northern Eurasia. Nor is there any evidence that they made the sea crossing to Australia and Papua New Guinea.
And thirdly, preceding both habilis and erectus:
Australopithecus sediba, found southern Africa 2010 - the immediate ancestor of Homo? That is the question.
In 2010, the remains of a species with an amalgam of australopithecine and Homo traits, dubbed Australopithecus sediba was discovered in southern Africa at a site north-west of Johannesburg in the form of two skeletons, possibly a boy aged about 9 years old and his mother who had apparently fallen into a deep cave[7]. Fossils from this period are comparatively rare – “so few that they would fit on a small table” in the words of Professor Lee Berger of the University of Witwatersrand in Johannesburg, who discovered and named the new species (others have used the term 'fit into a shoebox and still leave room for the shoes') – but these gaps are being filled as new fossils come to light. These recently discovered fossils had a small brain, long arms like an ape and short powerful hands, but they also walked upright with long legs capable of striding and possibly running like a human.
If sediba is to be considered as the genus Homo's immediate ancestor, as Berger claimed at the time, this would cast doubt on the view that the founding members of our species arose in East Africa. Sediba is said to provide a window into a critical period when our early human ancestors moved down from the trees to a life on the ground, and may be the transitional species between Australopithecus afarensis, or an unknown lineage, and the genus Homo – either Homo habilis, or even a direct ancestor of Homo erectus.
So let’s see what pans out and who, if any one, emerges triumphant?
To form an opinion on this, we will really have to survey the whole fossil panorama beginning many eons before these momentous events, in fact in the order of 6 million years ago and progressing, none too inexorably, from there:
In 2000, a team of French and Kenyan archaeologists working north of Nairobi, discovered a creature about 6 million years old called Orrorin tugenensis or, as he was named in the press in the press, “Millennium Man”. However, many paleontologists placed it on the chimp rather than the hominin side of the ledger. So let's have a look at the other possible candidates and groupings:
Ardipithecus group
Ardipithecus ramidus Kadabba, 5.2-5.8 Mya, found Great Rift Valley, Ethiopia
Similar criticisms have been levelled at another candidate, Ardipithecus ramidus Kadabba, some of whose remains were found in the Great Rift Valley of Ethiopia. These remains have been dated between 5.2 and 5.8 million years ago, including a toe bone whose shape suggests that this creature walked on two legs. In this context, most paleontologists agree that the decisive feature distinguishing hominins from apes is the ability to walk on two legs – bipedalism - but no one knows for sure when bipedalism evolved.
Ardithecus ramidus ramidus (‘Ardi’), 4.4 Mya, found Ethiopia 1994
In any event, the fossil evidence, thin as it is, shows that a number of bipedal species subsequently appeared, including Ardipithecus ramidus ramidus, whose remains were found in Ethiopia in 1994 and dated to ca. 4.4 million years ago, representing the first major adaptive radiation in the history of the hominins, probably associated with the advantages of bipedalism[8].
Australopithecines
Australopithecus anamensis, c.4.2 Mya, found Lake Turkana 1995
The next two hominin radiations are associated with a group of species that paleontologists refer to as australopithecines, all of which were bipedal. The oldest presently known is Australopithecus anamensis, a species whose remains were found in the Lake Turkana region in northern Kenya in 1995[9]. These have been dated to ca 4.2 mya. The Lake Turkana region, together with other sites in east and South Africa, possesses most of the fossil record of early human origins and our evolutionary journey since our lineage split from African apes more than seven million years ago[10]. For this reason, many anthropologists regard it as the cradle of humankind.
Australopithecus afarensis
Members of this species, so named after the Afar Valley in Ethiopia, where their fossils were found, survived in East Africa for 900,000 years from about 3.9 million years ago. It has been described as an “extremely successful species”[11]. The best known fragments were found in Ethiopia in the 1970s – 40% of a bipedal female christened as ‘Lucy’ along with other remains. (This find followed the discovery in March 2010 of a new human species that lived in Siberia 40,000 years ago dubbed X-woman)
Australopithecus africanus, 3.3-2.04 Mya
Australopithecus africanus was an early hominid, an australopithecine, who lived between ~ 3.03 and 2.04 million years ago in the later Pliocene and early Pleistocene. In common with the older Australopithecus afarensis, Au. africanus was of slender build, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that Au. africanus was significantly more like modern humans than Au. afarensis, with a more human-like cranium permitting a larger brain and more humanoid facial features. Au. africanus has been found at only four sites in southern Africa — Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992).[12]
More australopithecines
Then, in 1998, in South Africa, an even more complete australopithecine skeleton was found along with its skull, and dated to between 2.5 and 3.5 million years BP. Footprints of 3 australopithecines, known as the Laetoli footprints walking side by side, date from at least 3.5 to 3.7 Mya.
Australopithecus bahrelghazi, 3-3 Mya, found 1995 near the Great Rift Valley
In 1995, archaeologists working in Chad, well to the west of the Great Rift Valley, discovered the remains of a new species, Australopithecus bahrelghazi, which seems to have lived between 3 and 3.5 Mya. The several hundred australopithecines whose remains have been found in this century thus occupied a large area, reaching from Ethiopia to Chad in South Africa.
And in the mezzanine:
Paranthropus group
Paranthropus, 3-4 Mya, strong jaws
In a distinct radiation, there also appeared a second group of australopithecines of more robust appearance than afarensis. They existed between 3 and 4 million years ago and are sometimes assigned to a separate genus called Paranthropus. They evolved exceptionally strong jaws for the grinding of tough, fibrous plant foods, thereby marking them out as a different evolutionary line from us. Australopithecines were primarily vegetarians, but made occasional forays into meat eating.
The Hadar jaw, 2.3 Mya, found Ethiopia
Earlier finds such as a 2.3 million year old upper jaw from Hadar, Ethiopia, and also said to be the earliest trace of Homo, depend on a jaw fragment alone, whereas the sediba fossils mingle old and new versions of general features such as brain size and pelvis shape, and were it not for the fact that the bones were joined together, they may have been interpreted as belonging to entirely different creatures.
For example, the foot combines a heel bone like an ancient ape’s with an anklebone like homo’s. “The extreme mosaicism evident in sediba”, says Berger, “should be a lesson to palaeontologists”. Had he found any number of its bones in isolation, he would have classified them differently, he said: based on the pelvis, he would have said it was H. erectus. The arm alone suggests an ape. The anklebone is a match for a modern human’s.
Taking the Hadar Ethiopian jaw out of consideration, that would make sediba older than any of the well-known fossils but still younger than afarensis, putting it in "pole position" for the immediate ancestor of the genus Homo, Berger’s team contends. Furthermore considering sediba’s advanced features, the researchers suggest that it could be specifically ancestral to erectus (a portion of which is considered by some to be a different species called ergaster).
Therefore, instead of the traditional view in which afarensis begat habilis, which begat erectus, Berger says that Australopithecus africanus is the likely ancestor of sediba which then spawned erectus. If so, that would relegate habilis to a dead end side branch of the human family tree, and possibly also afarensis, long considered the ancestor of all later hominins, including africanus and homo[13]. The question is, is this then the lineage that ultimately gave rise to humankind as we know it?
Needless to say, Berger's views are the subject of some dispute. For example, William Kimbel of the Institute of Human Origins and Social Change at Arizona State University regards “his” (Hadar) jaw find in East Africa “clearly Homo” and dating from 300,000 earlier than sediba, and ridicules the suggestion that you need a whole skeleton before classification. Then, in March 2015, researchers unearthed a 2.8 million year old piece of lower jaw at Ledi-Geraru in north-eastern Ethiopia which they say is the earliest know representative of our genus with clear hallmarks of Homo as well as traits transitional between Australopithecus and Homo[14]. Its discoverers also do not accept that isolated fragments of anatomy cannot be reliably assigned to one taxonomic group or another. These and others regard the South African hominins as a separate radiation that took place in the south of the continent.
So, the most we can say thus far is that the origins of our genus Homo lie somewhere in a cloudy period between two and three million years ago. In an article in the National Geographic[15], Jamie Shreeve spells out the parameters: “On the far side of that divide are the ape like australopithecines, epitomised by Australopithecus afarensis and its most famous representative, Lucy, a skeleton discovered in Ethiopia in 1974. On the near side is Homo erectus, a tool-wielding, fire-making, globe-trotting species with a big brain and body proportions much like ours. Within that murky million-year gap, a bipedal animal was transformed into a nascent human being, a creature not just adapted to its environment but able to apply its mind to master it”. How did that revolution happen, queries Shreeve, when the fossil record is so "frustratingly ambiguous". This is the crux of the problem and brings us back to where we began.
H. habilis, discovered it may be remembered in 1964 and the 1970s by Louis Leakey and his son Richard, affords perhaps only a tenuous base for the human family tree, keeping it rooted in East Africa, and before that, the human story "goes dark", with just a few fossil fragments of Homo “too sketchy to warrant a species name”. Lee Berger has long argued that H habilis was “too primitive to deserve its privileged position at the root of our genus” (some say it’s really an Australopithecine) and Berger has been nearly alone in arguing that South (not East) Africa was the place to look for the true earliest Homo.
Then as previously noted, in 2008 he came up with Australopithecus sediba at Malapa in South Africa, and more recently in September 2013, in a cave system known as Rising Star, part of the Cradle of Humankind World Heritage Site in South Africa, he, with the aid of some svelte and supple cavers and paleontology students, discovered the hundreds of fossil remains of Homo naledi, most excavated from a pit a mere square yard wide. [15A]
Naledi was anticipated to be of some antiquity. Its fossils proved difficult to date because the skeletal remains were not compressed into or around rock or sediment. It had been anticipated that it may perhaps represent the founding member of out species. However, it eventually tallied out at a disappointing 236,000 to 335,000 years old, but despite the comparative youth of the bones when finally dated, Berger's team maintain that Naledi's primitive features link it to much earlier members of the human family, and perhaps even be a direct ancestor of H. sapiens. [15B]
The comparative youth of the samples would also seem to indicate that Naledi and another homo species shared the benefit of the earth’s bounty at the same time, which is significant because the new dating indicates that Naledi lived at a time when human ancestors were making sophisticated stone tools in the Middle Stone tradition, and many of the sites where archaeologists have discovered these tools do not contain any human fossils, so if the small brained Naledi was around at that time it cannot be excluded as the toolmaker.
It is still unknown how the specimens got into the extremely narrow opening to the cave in the first place, and why. The chamber is accessible only through a narrow chute, almost a hundred yards from the cave entrance. There appear to be no other entrance ways, and the speculation is that they may have been dropped from above as some form of burial ritual, which would be unusual for any form of primitive hominim at the time.
To elaborate, the specimens are an unusual combination of the primitive and the modern. Its brain was no larger than a baseball; as small as that of primitive austalopithecus afarensis (‘Lucy’). Yet the skull is as small as that of primitive austalopithecus afarensis (‘Lucy’), and its shape more like Homo erectus. The teeth are more habilis in distribution, but their shape has traits resembling Homo. The shoulder and fingers of the upper limb appear adapted to climbing, but the wrist and palm seem built for manipulating stone tools, a trait acquired by hominims after they abandoned life in the trees and evolved large inventive brains. The lower limb marries a Lucy like hip joint to a foot indistinguishable from our own. Its long legs and feet, nearly indistinguishable from a modern man, allowed it not only to walk upright, but also to travel for many kilometres at a time. These characteristics, and sediba's also, appear to contradict the idea that Homo’s toolmaking hand, big brain and small teeth evolved in concert[16].
The interpretation of the significance of the fossils at the time was upbeat: "The message we're getting is of an animal right on the cusp of the transition from Australopithecus to Homo. Everything that is touching the world in a critical way is like us. The other parts retain bits of their primitive past".[17],[18], but even then, voices were raised in dissent. One of the problems is how to define Homo. Some define the species on the basis of traits found in the cranium, jaw and teeth; others the bones below the head. Yet again others say that even if the remains turn out to be more than 2 million years old, that is not necessarily convincing enough evidence to suggest that naledi is on or near the path leading to our species. Stemming as they do from South Africa, a veritable cul-de-sac at the bottom of the African continent, according to Bernard Wood of George Washington University - whom we will meet again shortly - perhaps they constitute no more than a relic population similar to Homo floresiensis in Indonesia[19], below. We now know that naledi is of a far more youthful variety whose true significance is yet to be determined.
Found 2001-2004; fl 95,000 -50,000 yrs ago, Island of Flores, Indonesia
The fossilised remains of Homo floresiensis were first found on 2001 on the Indonesian island of Flores. These “Hobbit”-like creatures, so named because of their diminutive size, being no more than a metre tall, first appeared at Liang Bua cave, about 95,000 years ago. Previously, it was believed they had lived on Flores until quite recently (17,000 years ago), but new evidence in 2016 suggests they were extinct by around 50,000 years ago: https://theconversation.com/the-hobbits-were-extinct-much-earlier-than-first-thought-56922. Remains of at least 13 members of the species were unearthed between 2001 and 2004. The diminutive stature and small brain of the individuals of the species (about a third the brain size of Homo Sapiens) may have resulted from island dwarfism—an evolutionary process that results from long-term isolation on a small island with limited food resources and a lack of predators[20]. Pygmy elephants on Flores, now extinct, showed the same adaptation[21].
Two hypotheses were thought to account for the evolutionary origin of Homo floresiensis: the first is that Hobbits descended from Homo erectus, or “Java Man”, an archaic Asian hominin roughly similar in stature to us.[22] A small population of Homo erectus, it was thought, became marooned on Flores and shrunk in body size. The second hypothesis was that the ancestor of Homo floresiensis was an even more ancient hominin that was "pint-sized" to begin with. Candidates include Homo habilis or an Australopithecine, both known only from the fossil record of Africa.
Some light on this was shed following a five year search culminating in 2014 which revealed the discovery of hominin fossils discovered at Mata Menge, also on the island of Flores, comprising six teeth and a fragment from a lower jaw, representing the remains of at least three individual hominins (one adult and two young children).[23] The sandstone containing these fossils was deposited at least 700,000 years ago, which is ten times older than the Homo floresiensis skeleton from Liang Bua. These fossils tend to suggest that Homo floresiensis is indeed a kind of pygmy Homo erectus, and it now appears that these castaways dwarfed in size soon after making landfall on Flores (or another nearby island, such as Sulawesi). However, further evidence is awaited before a definitive pronouncement is made.
Found 2010 in Callao cave, Luzon Island, southern Philippines
Designated Homo luzonensis; probably only a little over a metres tall, but with some characteristics resembling older types of hominin such as Australopithecus. Initially only foot bones found, then three excavation seasons later, 12 more bone fragments from the same site, giving a total of seven teeth, two hand bones, three foot bones and one thigh bone, (unfortunately no skull), the remains of at least three individuals, a child and two adults dated to at least 50,000 years old, possibly older, a similar time frame to Homo floriensis. Found in the Calleo cave in northern Luzon. Also possibly descended from Homo erectus, or an Australopithecine or even Denisovan.
It is speculated that Homo luzonensis had a unique combination of features that justified it being classified as a new species. Thought to be similar to Homo floreniensis, but without bones from a complete adult arm or leg, it is impossible to calculate Homo luzonensis's height. Others are not convinced that there are enough fossil remains to justify the claim for a new species, nor to justify the dating.
Palaeontologist Gert van den Bergh of the University of Wollongong's Centre for Archaeological Science - who last year reported the discovery of 700,000-year-old tools used to butcher a rhinoceros at an open grassland site called Kalinga in the Cagayan Valley, 30 kilometres from the Callao Cave, this being the earliest evidence of hominin activity in the Philippines - thought it "highly likely" the fossils were from a separate to Homo floresiensis.
Philip Piper, an archaeologist at the Australian National University and co-author of the paper which appeared in Nature, thought to be no coincidence that new species are often found on islands, which are like “evolutionary places of experiment. The fact that there are so many islands in South-East Asia suggests it as being a place of diversity of hominins, akin to the Galapagos tortoises, each island in the Galapagos chain having its own species of tortoise.
Consequences: a fascinating case for a diverse range of ancient human species which evolved separately at the time across the islands of south-east Asia; opens up Pandora’s box in the context that stone tools on Sulawesi some 200,000 years old have already been found so further findings as to older hominin species await.[24]
Homo habilis, 2.3 Mya, found by Jonathan Leakey 1960s Olduvai Gorge, African Great Rift Valley, stone tools, varied diet
In the 1960s, in the Olduvai Gorge, a 50 km wide canyon in the Serengeti Plain in northern Tanzania that is part of the African Rift Valley, Jonathan Leakey found a hominin fossil about 1.4 metres tall, apparently of the same genus as human beings (Homo) which he therefore christened Homo habilis or ‘handy man’. This makes it the oldest species of the genus that included modern humans Homo habilis apparently had facility with the systematic manufacture and use of stone tools. Their brains were also a lot bigger than those of the australopithecines. This species was dated to around 2.3 Mya and it is thought may mark the real beginnings of human history. The use of tools made available a more varied diet, including meat, providing the metabolic energy for larger brains. It was also predominantly bipedal.
The Olduwan site was also occupied by P. boisei 1.8 million years ago, H. erectus 1.2 million years ago and H. sapiens 17,000 years ago.
Then, and perhaps on firmer ground: H. erectus (aka ergaster: African H. erectus), 1 Mya
Homo habilis lived in East Africa with several other species, including robust australopithecines (Paranthropus), and perhaps six or more different species of hominins lived at the time of habilis, but about one million years ago, various forms of homo erectus (also known as ergaster) [5.1] displaced all other forms of hominins. Homo ergaster specimens were taller than habilis, and had larger brains ranging from 850 to 1000 cc, close to the brain size in modern humans. From ca 1.5 mya, they began to manufacture a new type of stone tool with more sophistication than Oldawan tools. It is also likely that they had superior linguistic capabilities to those of habilis.
H. erectus migrations[6] This species included the first hominins to migrate out of East Africa and then out of Africa entirely into Eurasia. By about 700,000 years ago, communities of Homo erectus lived in parts of southern Asia and had even entered Ice Age Europe. Erectus remains were first found in Indonesia in 1891 and in the 1920s in the Zhoukoudian cave not too far from Beijing. It appears that erectus explored a wider variety of niches than habilis, and managed to live in regions whose climates would have been too cold or two seasonal for habilis. However, erectus did not manage to inhabit the cold heartland of northern Eurasia. Nor is there any evidence that they made the sea crossing to Australia and Papua New Guinea.
And thirdly, preceding both habilis and erectus:
Australopithecus sediba, found southern Africa 2010 - the immediate ancestor of Homo? That is the question.
In 2010, the remains of a species with an amalgam of australopithecine and Homo traits, dubbed Australopithecus sediba was discovered in southern Africa at a site north-west of Johannesburg in the form of two skeletons, possibly a boy aged about 9 years old and his mother who had apparently fallen into a deep cave[7]. Fossils from this period are comparatively rare – “so few that they would fit on a small table” in the words of Professor Lee Berger of the University of Witwatersrand in Johannesburg, who discovered and named the new species (others have used the term 'fit into a shoebox and still leave room for the shoes') – but these gaps are being filled as new fossils come to light. These recently discovered fossils had a small brain, long arms like an ape and short powerful hands, but they also walked upright with long legs capable of striding and possibly running like a human.
If sediba is to be considered as the genus Homo's immediate ancestor, as Berger claimed at the time, this would cast doubt on the view that the founding members of our species arose in East Africa. Sediba is said to provide a window into a critical period when our early human ancestors moved down from the trees to a life on the ground, and may be the transitional species between Australopithecus afarensis, or an unknown lineage, and the genus Homo – either Homo habilis, or even a direct ancestor of Homo erectus.
So let’s see what pans out and who, if any one, emerges triumphant?
To form an opinion on this, we will really have to survey the whole fossil panorama beginning many eons before these momentous events, in fact in the order of 6 million years ago and progressing, none too inexorably, from there:
In 2000, a team of French and Kenyan archaeologists working north of Nairobi, discovered a creature about 6 million years old called Orrorin tugenensis or, as he was named in the press in the press, “Millennium Man”. However, many paleontologists placed it on the chimp rather than the hominin side of the ledger. So let's have a look at the other possible candidates and groupings:
Ardipithecus group
Ardipithecus ramidus Kadabba, 5.2-5.8 Mya, found Great Rift Valley, Ethiopia
Similar criticisms have been levelled at another candidate, Ardipithecus ramidus Kadabba, some of whose remains were found in the Great Rift Valley of Ethiopia. These remains have been dated between 5.2 and 5.8 million years ago, including a toe bone whose shape suggests that this creature walked on two legs. In this context, most paleontologists agree that the decisive feature distinguishing hominins from apes is the ability to walk on two legs – bipedalism - but no one knows for sure when bipedalism evolved.
Ardithecus ramidus ramidus (‘Ardi’), 4.4 Mya, found Ethiopia 1994
In any event, the fossil evidence, thin as it is, shows that a number of bipedal species subsequently appeared, including Ardipithecus ramidus ramidus, whose remains were found in Ethiopia in 1994 and dated to ca. 4.4 million years ago, representing the first major adaptive radiation in the history of the hominins, probably associated with the advantages of bipedalism[8].
Australopithecines
Australopithecus anamensis, c.4.2 Mya, found Lake Turkana 1995
The next two hominin radiations are associated with a group of species that paleontologists refer to as australopithecines, all of which were bipedal. The oldest presently known is Australopithecus anamensis, a species whose remains were found in the Lake Turkana region in northern Kenya in 1995[9]. These have been dated to ca 4.2 mya. The Lake Turkana region, together with other sites in east and South Africa, possesses most of the fossil record of early human origins and our evolutionary journey since our lineage split from African apes more than seven million years ago[10]. For this reason, many anthropologists regard it as the cradle of humankind.
Australopithecus afarensis
Members of this species, so named after the Afar Valley in Ethiopia, where their fossils were found, survived in East Africa for 900,000 years from about 3.9 million years ago. It has been described as an “extremely successful species”[11]. The best known fragments were found in Ethiopia in the 1970s – 40% of a bipedal female christened as ‘Lucy’ along with other remains. (This find followed the discovery in March 2010 of a new human species that lived in Siberia 40,000 years ago dubbed X-woman)
Australopithecus africanus, 3.3-2.04 Mya
Australopithecus africanus was an early hominid, an australopithecine, who lived between ~ 3.03 and 2.04 million years ago in the later Pliocene and early Pleistocene. In common with the older Australopithecus afarensis, Au. africanus was of slender build, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that Au. africanus was significantly more like modern humans than Au. afarensis, with a more human-like cranium permitting a larger brain and more humanoid facial features. Au. africanus has been found at only four sites in southern Africa — Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992).[12]
More australopithecines
Then, in 1998, in South Africa, an even more complete australopithecine skeleton was found along with its skull, and dated to between 2.5 and 3.5 million years BP. Footprints of 3 australopithecines, known as the Laetoli footprints walking side by side, date from at least 3.5 to 3.7 Mya.
Australopithecus bahrelghazi, 3-3 Mya, found 1995 near the Great Rift Valley
In 1995, archaeologists working in Chad, well to the west of the Great Rift Valley, discovered the remains of a new species, Australopithecus bahrelghazi, which seems to have lived between 3 and 3.5 Mya. The several hundred australopithecines whose remains have been found in this century thus occupied a large area, reaching from Ethiopia to Chad in South Africa.
And in the mezzanine:
Paranthropus group
Paranthropus, 3-4 Mya, strong jaws
In a distinct radiation, there also appeared a second group of australopithecines of more robust appearance than afarensis. They existed between 3 and 4 million years ago and are sometimes assigned to a separate genus called Paranthropus. They evolved exceptionally strong jaws for the grinding of tough, fibrous plant foods, thereby marking them out as a different evolutionary line from us. Australopithecines were primarily vegetarians, but made occasional forays into meat eating.
The Hadar jaw, 2.3 Mya, found Ethiopia
Earlier finds such as a 2.3 million year old upper jaw from Hadar, Ethiopia, and also said to be the earliest trace of Homo, depend on a jaw fragment alone, whereas the sediba fossils mingle old and new versions of general features such as brain size and pelvis shape, and were it not for the fact that the bones were joined together, they may have been interpreted as belonging to entirely different creatures.
For example, the foot combines a heel bone like an ancient ape’s with an anklebone like homo’s. “The extreme mosaicism evident in sediba”, says Berger, “should be a lesson to palaeontologists”. Had he found any number of its bones in isolation, he would have classified them differently, he said: based on the pelvis, he would have said it was H. erectus. The arm alone suggests an ape. The anklebone is a match for a modern human’s.
Taking the Hadar Ethiopian jaw out of consideration, that would make sediba older than any of the well-known fossils but still younger than afarensis, putting it in "pole position" for the immediate ancestor of the genus Homo, Berger’s team contends. Furthermore considering sediba’s advanced features, the researchers suggest that it could be specifically ancestral to erectus (a portion of which is considered by some to be a different species called ergaster).
Therefore, instead of the traditional view in which afarensis begat habilis, which begat erectus, Berger says that Australopithecus africanus is the likely ancestor of sediba which then spawned erectus. If so, that would relegate habilis to a dead end side branch of the human family tree, and possibly also afarensis, long considered the ancestor of all later hominins, including africanus and homo[13]. The question is, is this then the lineage that ultimately gave rise to humankind as we know it?
Needless to say, Berger's views are the subject of some dispute. For example, William Kimbel of the Institute of Human Origins and Social Change at Arizona State University regards “his” (Hadar) jaw find in East Africa “clearly Homo” and dating from 300,000 earlier than sediba, and ridicules the suggestion that you need a whole skeleton before classification. Then, in March 2015, researchers unearthed a 2.8 million year old piece of lower jaw at Ledi-Geraru in north-eastern Ethiopia which they say is the earliest know representative of our genus with clear hallmarks of Homo as well as traits transitional between Australopithecus and Homo[14]. Its discoverers also do not accept that isolated fragments of anatomy cannot be reliably assigned to one taxonomic group or another. These and others regard the South African hominins as a separate radiation that took place in the south of the continent.
So, the most we can say thus far is that the origins of our genus Homo lie somewhere in a cloudy period between two and three million years ago. In an article in the National Geographic[15], Jamie Shreeve spells out the parameters: “On the far side of that divide are the ape like australopithecines, epitomised by Australopithecus afarensis and its most famous representative, Lucy, a skeleton discovered in Ethiopia in 1974. On the near side is Homo erectus, a tool-wielding, fire-making, globe-trotting species with a big brain and body proportions much like ours. Within that murky million-year gap, a bipedal animal was transformed into a nascent human being, a creature not just adapted to its environment but able to apply its mind to master it”. How did that revolution happen, queries Shreeve, when the fossil record is so "frustratingly ambiguous". This is the crux of the problem and brings us back to where we began.
H. habilis, discovered it may be remembered in 1964 and the 1970s by Louis Leakey and his son Richard, affords perhaps only a tenuous base for the human family tree, keeping it rooted in East Africa, and before that, the human story "goes dark", with just a few fossil fragments of Homo “too sketchy to warrant a species name”. Lee Berger has long argued that H habilis was “too primitive to deserve its privileged position at the root of our genus” (some say it’s really an Australopithecine) and Berger has been nearly alone in arguing that South (not East) Africa was the place to look for the true earliest Homo.
Then as previously noted, in 2008 he came up with Australopithecus sediba at Malapa in South Africa, and more recently in September 2013, in a cave system known as Rising Star, part of the Cradle of Humankind World Heritage Site in South Africa, he, with the aid of some svelte and supple cavers and paleontology students, discovered the hundreds of fossil remains of Homo naledi, most excavated from a pit a mere square yard wide. [15A]
Naledi was anticipated to be of some antiquity. Its fossils proved difficult to date because the skeletal remains were not compressed into or around rock or sediment. It had been anticipated that it may perhaps represent the founding member of out species. However, it eventually tallied out at a disappointing 236,000 to 335,000 years old, but despite the comparative youth of the bones when finally dated, Berger's team maintain that Naledi's primitive features link it to much earlier members of the human family, and perhaps even be a direct ancestor of H. sapiens. [15B]
The comparative youth of the samples would also seem to indicate that Naledi and another homo species shared the benefit of the earth’s bounty at the same time, which is significant because the new dating indicates that Naledi lived at a time when human ancestors were making sophisticated stone tools in the Middle Stone tradition, and many of the sites where archaeologists have discovered these tools do not contain any human fossils, so if the small brained Naledi was around at that time it cannot be excluded as the toolmaker.
It is still unknown how the specimens got into the extremely narrow opening to the cave in the first place, and why. The chamber is accessible only through a narrow chute, almost a hundred yards from the cave entrance. There appear to be no other entrance ways, and the speculation is that they may have been dropped from above as some form of burial ritual, which would be unusual for any form of primitive hominim at the time.
To elaborate, the specimens are an unusual combination of the primitive and the modern. Its brain was no larger than a baseball; as small as that of primitive austalopithecus afarensis (‘Lucy’). Yet the skull is as small as that of primitive austalopithecus afarensis (‘Lucy’), and its shape more like Homo erectus. The teeth are more habilis in distribution, but their shape has traits resembling Homo. The shoulder and fingers of the upper limb appear adapted to climbing, but the wrist and palm seem built for manipulating stone tools, a trait acquired by hominims after they abandoned life in the trees and evolved large inventive brains. The lower limb marries a Lucy like hip joint to a foot indistinguishable from our own. Its long legs and feet, nearly indistinguishable from a modern man, allowed it not only to walk upright, but also to travel for many kilometres at a time. These characteristics, and sediba's also, appear to contradict the idea that Homo’s toolmaking hand, big brain and small teeth evolved in concert[16].
The interpretation of the significance of the fossils at the time was upbeat: "The message we're getting is of an animal right on the cusp of the transition from Australopithecus to Homo. Everything that is touching the world in a critical way is like us. The other parts retain bits of their primitive past".[17],[18], but even then, voices were raised in dissent. One of the problems is how to define Homo. Some define the species on the basis of traits found in the cranium, jaw and teeth; others the bones below the head. Yet again others say that even if the remains turn out to be more than 2 million years old, that is not necessarily convincing enough evidence to suggest that naledi is on or near the path leading to our species. Stemming as they do from South Africa, a veritable cul-de-sac at the bottom of the African continent, according to Bernard Wood of George Washington University - whom we will meet again shortly - perhaps they constitute no more than a relic population similar to Homo floresiensis in Indonesia[19], below. We now know that naledi is of a far more youthful variety whose true significance is yet to be determined.
Found 2001-2004; fl 95,000 -50,000 yrs ago, Island of Flores, Indonesia
The fossilised remains of Homo floresiensis were first found on 2001 on the Indonesian island of Flores. These “Hobbit”-like creatures, so named because of their diminutive size, being no more than a metre tall, first appeared at Liang Bua cave, about 95,000 years ago. Previously, it was believed they had lived on Flores until quite recently (17,000 years ago), but new evidence in 2016 suggests they were extinct by around 50,000 years ago: https://theconversation.com/the-hobbits-were-extinct-much-earlier-than-first-thought-56922. Remains of at least 13 members of the species were unearthed between 2001 and 2004. The diminutive stature and small brain of the individuals of the species (about a third the brain size of Homo Sapiens) may have resulted from island dwarfism—an evolutionary process that results from long-term isolation on a small island with limited food resources and a lack of predators[20]. Pygmy elephants on Flores, now extinct, showed the same adaptation[21].
Two hypotheses were thought to account for the evolutionary origin of Homo floresiensis: the first is that Hobbits descended from Homo erectus, or “Java Man”, an archaic Asian hominin roughly similar in stature to us.[22] A small population of Homo erectus, it was thought, became marooned on Flores and shrunk in body size. The second hypothesis was that the ancestor of Homo floresiensis was an even more ancient hominin that was "pint-sized" to begin with. Candidates include Homo habilis or an Australopithecine, both known only from the fossil record of Africa.
Some light on this was shed following a five year search culminating in 2014 which revealed the discovery of hominin fossils discovered at Mata Menge, also on the island of Flores, comprising six teeth and a fragment from a lower jaw, representing the remains of at least three individual hominins (one adult and two young children).[23] The sandstone containing these fossils was deposited at least 700,000 years ago, which is ten times older than the Homo floresiensis skeleton from Liang Bua. These fossils tend to suggest that Homo floresiensis is indeed a kind of pygmy Homo erectus, and it now appears that these castaways dwarfed in size soon after making landfall on Flores (or another nearby island, such as Sulawesi). However, further evidence is awaited before a definitive pronouncement is made.
Found 2010 in Callao cave, Luzon Island, southern Philippines
Designated Homo luzonensis; probably only a little over a metres tall, but with some characteristics resembling older types of hominin such as Australopithecus. Initially only foot bones found, then three excavation seasons later, 12 more bone fragments from the same site, giving a total of seven teeth, two hand bones, three foot bones and one thigh bone, (unfortunately no skull), the remains of at least three individuals, a child and two adults dated to at least 50,000 years old, possibly older, a similar time frame to Homo floriensis. Found in the Calleo cave in northern Luzon. Also possibly descended from Homo erectus, or an Australopithecine or even Denisovan.
It is speculated that Homo luzonensis had a unique combination of features that justified it being classified as a new species. Thought to be similar to Homo floreniensis, but without bones from a complete adult arm or leg, it is impossible to calculate Homo luzonensis's height. Others are not convinced that there are enough fossil remains to justify the claim for a new species, nor to justify the dating.
Palaeontologist Gert van den Bergh of the University of Wollongong's Centre for Archaeological Science - who last year reported the discovery of 700,000-year-old tools used to butcher a rhinoceros at an open grassland site called Kalinga in the Cagayan Valley, 30 kilometres from the Callao Cave, this being the earliest evidence of hominin activity in the Philippines - thought it "highly likely" the fossils were from a separate to Homo floresiensis.
Philip Piper, an archaeologist at the Australian National University and co-author of the paper which appeared in Nature, thought to be no coincidence that new species are often found on islands, which are like “evolutionary places of experiment. The fact that there are so many islands in South-East Asia suggests it as being a place of diversity of hominins, akin to the Galapagos tortoises, each island in the Galapagos chain having its own species of tortoise.
Consequences: a fascinating case for a diverse range of ancient human species which evolved separately at the time across the islands of south-east Asia; opens up Pandora’s box in the context that stone tools on Sulawesi some 200,000 years old have already been found so further findings as to older hominin species await.[24]
Map of Flores showing the locations of Liang Bua cave (the original ‘Hobbit’ site) and the open site of Mata Menge in the So'a Basin, where fossils of ancient Hobbit-like creatures have now been found. LGM: Last Glacial Maximum (~22,000-19,000 years ago).
Source:
http://theconversation.com/a-700-000-year-old-fossil-find-shows-the-hobbits-ancestors-were-even-smaller-60192
So who is right in this quest for origins? Naledi's comparative youth would be disappointing for those who asserted a probable far more ancient lineage for those fossil finds but perhaps in any event, the last word should come from Rene Bobe of George Washington University: “If you find [hominin] populations distributed across Africa, evolving in different ways, why would the one you find be the ancestor?” But there is yet another aspect to be considered below, and Bernard Wood has something to say about that too.
[1] Bill Bryson, A Short History of Nearly Everything, Broadway Book, 2003, 321-2.
[2] Ibid, 441.
[3] Ibid, 449.
[4] Ibid, Chapter 28, "The mysterious Biped".
[5] The history of these developments is recounted in an article entitled "Mystery man" in the National Geographic, October 2015, 30-57. See also www.nytimes.com/2015/09/11/science/south-africa-fossils-new-species-human-ancestor-homo-naledi.html?_r=0
[5.1] See also Richard Dawkins and Yan Wong, The Ancestor's Tale - A Pilgrimage to the Dawn of Life, Weidenfeld Nicolson, London, 2004, 2nd edition, 2016, 81, noted on the page Climate change, toolmaking and language as factors influencing hominin diversity
[6] David Christian, Maps of Time, op cit, 164-5.
[7] “Face to face with the 2 million-year-old ‘missing link’”, SMH, 9 April 2010; see also Kate Wong, “Human Evolution – First of Our Kind”, New Scientist, April 2012, 21-29.
[8] The story and significance of the discovery of Ardipithecus ramidus, nicknamed Ardi, at Aramis in the Middle Awash region of the Afir Basin in Africa appears in an article by Jamie Shreeve “The Evolutionary Road”, National Geographic, July 2010, 35ff, where the possible evolutionary path from the Ardipithecus to the Australopithecus species is reviewed, as is the significance of the Great Rift Valley in East Africa for this kind of archaeological excavation. See also “The birth of bipedalism 4.4 million years ago” in the same edition at 64ff. A chart from this article depicting “The human family” for the last 6 million years appears in Appendix 1.
[9] The story of discovery of Turkana Boy’s fossilised remains is told in the second episode of the WGBH DVD Becoming Human – Unearthing our earliest ancestors.
[10] Peter B. de Menocal, Professor at Lamont-Doherty Earth Observatory, Columbia University, “Climate Shocks – Where we came from”, Scientific American, September 2014, 34-37.
[11] Ibid at 36. Stone markings on animal bones discovered in Ethiopia have led scientists to conclude that early humans used sharp edged stones as tools to remove flesh from animals around 3.3 million years ago. Australopithecus afarensis was the only early human known to exist at this time: See ‘Tool time started a million years earlier for human ancestors”, SMH, 12 August 2010.
[12] Source: https://en.wikipedia.org/wiki/Australopithecus_africanus
[13] Kate Wong, “Human Evolution – First of Our Kind”, New Scientist, April 2012, 21at 24.
[14] Kate Wong, "Mystery Human", Scientific American, March 2016, 20 at 28. See also f/n [18] below.
[15] Jamie Shreeve, "Mystery Man", National Geographic, October 2015, 20- 57.
[15A] Reported in Nikki Phillips, "Underground astronauts dig up fossils. New species of man ... Make no bones about it", SMH, September 12-13, 2015.
[15B] The dating results were published online on 9 May 2017: Kate Wong, "Our cousin Neo", Scientific American, August 2017, 47. Neo is a reference to even more fossils found in a second chamber in the Rising Star cave, including a skeleton of a adult male named Neo, meaning 'gift' in the local Soweto language.
[16] Kate Wong, "Mystery Human", Scientific American, March 2016, 20 at 25.
[17] Shreeve, op cit, at 45.
[18] At a meeting of noted paleontologists working in East Africa in August 2014 to celebrate the 50th anniversary of Louis Leakey's description of H. habilis, at which Berger was present to announce his discoveries, Bill Kimbel described another Homo jaw from Ethiopia dated 2.8 mya – the oldest member of our genus yet, and archaeologist Sonia Hammond from Stoney Book University mentioned the discovery of crude stone tools near Lake Turkana dating to 3.3 mya, half a million years before the appearance of our own genus: Shreeve, ibid, 54-5.
[19] Kate Wong, "Mystery Human", op cit, 20 at 28.
[20] Another suggestion, quickly rejected by hobbit team members, is that the individual who housed the skeleton may have been afflicted by Down’s syndrome: Kate Wong, “Human or hobbit”, Scientific American, November 2014, 13. A 2D image of what a female skeletal version of Homo floresiensis may have looked like created by Dr Susan Hayes, a facial anthropologist, may be found in the article “Now, my precious hobbit, it’s time to face the truth”, SMH, 11 December 2012, p 5.
[21] Smithsonian Museum of Natural History, “What does it mean to be human”: http://humanorigins.si.edu/evidence/human-fossils/species/homo-floresiensis
[22] Article by Gerrit (Gert) van den Bergh, researcher in palaeontology, University of Wollongong and Adam Brumm, Senior Research Fellow, Griffith University: "A 700,000-year-old fossil find shows the Hobbits’ ancestors were even smaller" at
http://theconversation.com/a-700-000-year-old-fossil-find-shows-the-hobbits-ancestors-were-even-smaller-60192
[23] Ibid. Other articles on the same subject-matter appear at https://www.rt.com/viral/346025-700000-yr-old-hobbit-fossils/ and http://news.nationalgeographic.com/2016/06/hobbits-humans-older-ancestors-island-fossils-archaeology/
[24] Stuart Layt, "Meet the parents: new species of ancient 'hobbits' found", Sydney Morning Herald, 11 April 2019; https://www.abc.net.au/news/science/2019-04-11/new-species-of-early-human-found-in-a-cave-on-the-philippines/10985676
More like a bush or a braided stream than a tree
The notion of human evolution as a never-ending “march of progress” - from a knuckle-walking chimp-like ape, through a series of intermediary protohumans, and finally to our elegant striding upright form is apt to be misleading[1]. It was once suggested that the evidence all pointed in a single direction: fingers shortened, big toes came into forward alignment, and the head shifted to rest upon a vertical back. But that has been shown to be far from the truth.
What we can say is that it would appear that the common ancestor we share with chimpanzees lived about six million years ago, or a bit earlier, and all members of the genus homo are descended from ancestors belonging to the genus we call Australopithecus, or ‘southern ape’. We have only a poor fossil record connecting Australopithecus to the presumably quadrupedal ancestor that we share with chimpanzees, and we don’t know how our ancestors originally rose up on their hind legs. Evolutionary intermediates after that are characterised by increasing brain size and upwards walking, but as Darwin himself said: “In a series of forms graduating insensibly from some apelike creature to man as he now exists, it would be impossible to fix on any definite point where the term ‘man’ ought to be used”. In the same context, Richard Dawkins makes the pertinent observation that the changes that take place within an individual’s lifetime, as it grows up, are in any case much more dramatic than the changes we see as we compare adults in successive generations from child to old age.[2]
The discovery of Ardipithecus ramidus, the 4.4 million year old ‘Ardi’ skeleton described above and another find at Burtele in Ethiopia’s central Afar region indicate that we probably came from a convoluted tree of humans, and that the ostensibly human hallmark of walking upright may have developed more than once. Rigid feet and domed metatarsal heads suggest that Ardi could get around bipedally while on the ground, while her upper body still has features such as fairly long features and arms suggestive of an agile tree climber.
The other find at Burtele also dates to 3.4 million years ago. It consists of only eight small foot bones, but researchers are confident that it represents a new hominim species, and one that was prominently arboreal, despite living at the same time as the bipedal Australopithecus afarensis, (Lucy) a probable direct descendant of ours. This underscores the fact that our status as the only surviving hominim (Neanderthals having gone extinct some 28,000 years ago and the hobbit-like Homo floresiensis about 50,000 years ago) is probably the exception in human evolution rather than the rule, with overlapping forbears cropping up repeatedly[3]. Now that researchers have evidence that two very different hominims – the Burtele species and Lucy – were living at roughly the same time, it is evident that both new and old hominesque fossils will have to be closely re-examined to determine which species they belong to rather than just being assigned to a reigning hominim of that particular era.
Another study has made findings tending to similar effect, namely that nearly two million years ago, homo erectus and his tool-making relative homo habilis (handyman) were probably contemporaries of an even older species called homo rudolfensis, meaning that “human evolution (is) not the straight line that it once was (thought to be)”.
The rudolfensis remains were dug up from sediment dating to the Pleistocene period at a location east of Lake Turkana in northern Kenya between 2007 and 2009. The skull lacked a lower jaw bone. However, within 3 years three other fossils were located within a 10 km radius and found to be attributable to the same species and dated to between 1.78 and 1.95 mya. Scans were used in a virtual reconstruction of the lower jaw, which proved a good fit with upper law of the original find, known as 1470 for short. The findings help to confirm the existence of a distinctive kind of early human nearly 2 million years ago, and not simply a misshapen habilis[4]. The two species probably kept out of each other’s way and ate different foods, the authors of the study surmise.
These themes were taken up by Bernard Wood, a medically trained paleoanthropologist at George Washington University, in an article in Scientific American in 2014[5]. As he says, fifty years ago, tracing the evolutionary ancestors of Homo sapiens was generally thought to be a relatively straightforward matter - from Ardipithecus to Australopithecus (in southern Africa), to Homo erectus (spreading from Asia to Europe) to Homo sapiens, that is, modern humans. In other words, the progression was linear, and each of the various forerunners, were understood to be the direct ancestors of modern humans. Only robust australopithecus was thought to constitute a rather distant relative rather than a direct forebear. It was rather like Darwin’s Tree of Life - with all the species alive today on the outer extremities of the tree and all the species no longer extant near the trunk.
The discoveries of early hominim fossil remains in Olduvai Gorge at sites close to the Eastern Rift Valley in East Africa dating back more than one million years changed that. The fossils in this area have been found in sediments laid down along lakes or along riverbanks. Because they are open air sites, the strata incorporate ash expelled from the many volcanoes generated in and around the eastern Rift valley by the movement of tectonic plates. This gives researchers the means of establishing the age of the strata independent of the fossils they contain, and because they function like “a series of date-stamped blankets” thrown over the region, they allow researchers to correlate fossils deposited thousands of miles apart.
The strata in this cover millions of years of time, meaning that it is possible to give minimum “start” and “finish” dates for each particular group of fossil hominims, signifying that even within East Africa, let alone between east and Southern Africa, there were many times in the past 1-4 million years when more than one and in some periods, several, hominims lived contemporaneously.
For example, from roughly 2.3 million to 1.4 million years ago, a period of about one million years, two very different kinds of hominim, Paranthropus boisei and Homo habilis lived in the same region of East Africa. Therefore, one and perhaps both, were not ancestral to modern human beings. There is also evidence of multiple lineages in our more recent past:
Thus our recent evolutionary history is much “bushier” than people thought even 10 years ago. In fact one may describe it as more like a bundle of twigs with genetic and fossil evidence revealing that closely related hominin species shared the planet many times in the past few million years, making it more difficult to identify direct ancestors of modern humans than scientists anticipated even 20 years ago.
Another analogy which has recently been utilised is that of a braided stream: “a river that divides into channels, only to merge again downstream". Similarly, the various hominim types that inhabited the landscapes of Africa must at at some point have diverged from a common ancestor, but then further down the river of time, they may have coalasced again, so that we, at the river’s mouth, carry in us today a bit of East Africa, a bit of South Africa and a whole lot of history we have no notion of whatsoever”.[6] Perhaps this should not be thought of as surprising. The same applies to many groups of mammals, so why should hominins have been any different.
Nevertheless, critics of the bushy tree approach have charged that paleoanthropologists have been overzealous in identifying new species from their finds. Wood’s view is that there are sound logical reasons to suspect that the fossil record always underestimates the number of species. Secondly, many uncontested species are difficult to detect using bones and teeth, which is all that survives into the fossil record; and furthermore, most of the mammal species that were living between 3 million and one million years ago have no direct living descendants, and therefore the existence of several contemporary early hominins with no direct living descendants should not appear “odd” at all [7].
[1] Katherine Harmon, “Scattered Ancestry”, Scientific American, February 2013, 36 at 37.
[2] Richard Dawkins, The Greatest Show on Earth, 198. 204-7.
[3] For an illustration, see Appendix 2.
[4] See “Early man not alone, study finds”, SMH, 9 August 2012. The findings were originally published in the Journal Nature. For a depiction of homo rudolfensis, see Appendix 3 from the Smithsonian Exhibition on Life and the Oceans, October 2010.
[5] “Welcome to the family”, September 2014, 27-31.
[6] Jamie Shreeve, "Mystery Man", National Geographic, October 2015, 20 at 56.
[7] Bernard Wood, op cit.
"More like a bush, than a tree"
[1] Bill Bryson, A Short History of Nearly Everything, Broadway Book, 2003, 321-2.
[2] Ibid, 441.
[3] Ibid, 449.
[4] Ibid, Chapter 28, "The mysterious Biped".
[5] The history of these developments is recounted in an article entitled "Mystery man" in the National Geographic, October 2015, 30-57. See also www.nytimes.com/2015/09/11/science/south-africa-fossils-new-species-human-ancestor-homo-naledi.html?_r=0
[5.1] See also Richard Dawkins and Yan Wong, The Ancestor's Tale - A Pilgrimage to the Dawn of Life, Weidenfeld Nicolson, London, 2004, 2nd edition, 2016, 81, noted on the page Climate change, toolmaking and language as factors influencing hominin diversity
[6] David Christian, Maps of Time, op cit, 164-5.
[7] “Face to face with the 2 million-year-old ‘missing link’”, SMH, 9 April 2010; see also Kate Wong, “Human Evolution – First of Our Kind”, New Scientist, April 2012, 21-29.
[8] The story and significance of the discovery of Ardipithecus ramidus, nicknamed Ardi, at Aramis in the Middle Awash region of the Afir Basin in Africa appears in an article by Jamie Shreeve “The Evolutionary Road”, National Geographic, July 2010, 35ff, where the possible evolutionary path from the Ardipithecus to the Australopithecus species is reviewed, as is the significance of the Great Rift Valley in East Africa for this kind of archaeological excavation. See also “The birth of bipedalism 4.4 million years ago” in the same edition at 64ff. A chart from this article depicting “The human family” for the last 6 million years appears in Appendix 1.
[9] The story of discovery of Turkana Boy’s fossilised remains is told in the second episode of the WGBH DVD Becoming Human – Unearthing our earliest ancestors.
[10] Peter B. de Menocal, Professor at Lamont-Doherty Earth Observatory, Columbia University, “Climate Shocks – Where we came from”, Scientific American, September 2014, 34-37.
[11] Ibid at 36. Stone markings on animal bones discovered in Ethiopia have led scientists to conclude that early humans used sharp edged stones as tools to remove flesh from animals around 3.3 million years ago. Australopithecus afarensis was the only early human known to exist at this time: See ‘Tool time started a million years earlier for human ancestors”, SMH, 12 August 2010.
[12] Source: https://en.wikipedia.org/wiki/Australopithecus_africanus
[13] Kate Wong, “Human Evolution – First of Our Kind”, New Scientist, April 2012, 21at 24.
[14] Kate Wong, "Mystery Human", Scientific American, March 2016, 20 at 28. See also f/n [18] below.
[15] Jamie Shreeve, "Mystery Man", National Geographic, October 2015, 20- 57.
[15A] Reported in Nikki Phillips, "Underground astronauts dig up fossils. New species of man ... Make no bones about it", SMH, September 12-13, 2015.
[15B] The dating results were published online on 9 May 2017: Kate Wong, "Our cousin Neo", Scientific American, August 2017, 47. Neo is a reference to even more fossils found in a second chamber in the Rising Star cave, including a skeleton of a adult male named Neo, meaning 'gift' in the local Soweto language.
[16] Kate Wong, "Mystery Human", Scientific American, March 2016, 20 at 25.
[17] Shreeve, op cit, at 45.
[18] At a meeting of noted paleontologists working in East Africa in August 2014 to celebrate the 50th anniversary of Louis Leakey's description of H. habilis, at which Berger was present to announce his discoveries, Bill Kimbel described another Homo jaw from Ethiopia dated 2.8 mya – the oldest member of our genus yet, and archaeologist Sonia Hammond from Stoney Book University mentioned the discovery of crude stone tools near Lake Turkana dating to 3.3 mya, half a million years before the appearance of our own genus: Shreeve, ibid, 54-5.
[19] Kate Wong, "Mystery Human", op cit, 20 at 28.
[20] Another suggestion, quickly rejected by hobbit team members, is that the individual who housed the skeleton may have been afflicted by Down’s syndrome: Kate Wong, “Human or hobbit”, Scientific American, November 2014, 13. A 2D image of what a female skeletal version of Homo floresiensis may have looked like created by Dr Susan Hayes, a facial anthropologist, may be found in the article “Now, my precious hobbit, it’s time to face the truth”, SMH, 11 December 2012, p 5.
[21] Smithsonian Museum of Natural History, “What does it mean to be human”: http://humanorigins.si.edu/evidence/human-fossils/species/homo-floresiensis
[22] Article by Gerrit (Gert) van den Bergh, researcher in palaeontology, University of Wollongong and Adam Brumm, Senior Research Fellow, Griffith University: "A 700,000-year-old fossil find shows the Hobbits’ ancestors were even smaller" at
http://theconversation.com/a-700-000-year-old-fossil-find-shows-the-hobbits-ancestors-were-even-smaller-60192
[23] Ibid. Other articles on the same subject-matter appear at https://www.rt.com/viral/346025-700000-yr-old-hobbit-fossils/ and http://news.nationalgeographic.com/2016/06/hobbits-humans-older-ancestors-island-fossils-archaeology/
[24] Stuart Layt, "Meet the parents: new species of ancient 'hobbits' found", Sydney Morning Herald, 11 April 2019; https://www.abc.net.au/news/science/2019-04-11/new-species-of-early-human-found-in-a-cave-on-the-philippines/10985676
More like a bush or a braided stream than a tree
The notion of human evolution as a never-ending “march of progress” - from a knuckle-walking chimp-like ape, through a series of intermediary protohumans, and finally to our elegant striding upright form is apt to be misleading[1]. It was once suggested that the evidence all pointed in a single direction: fingers shortened, big toes came into forward alignment, and the head shifted to rest upon a vertical back. But that has been shown to be far from the truth.
What we can say is that it would appear that the common ancestor we share with chimpanzees lived about six million years ago, or a bit earlier, and all members of the genus homo are descended from ancestors belonging to the genus we call Australopithecus, or ‘southern ape’. We have only a poor fossil record connecting Australopithecus to the presumably quadrupedal ancestor that we share with chimpanzees, and we don’t know how our ancestors originally rose up on their hind legs. Evolutionary intermediates after that are characterised by increasing brain size and upwards walking, but as Darwin himself said: “In a series of forms graduating insensibly from some apelike creature to man as he now exists, it would be impossible to fix on any definite point where the term ‘man’ ought to be used”. In the same context, Richard Dawkins makes the pertinent observation that the changes that take place within an individual’s lifetime, as it grows up, are in any case much more dramatic than the changes we see as we compare adults in successive generations from child to old age.[2]
The discovery of Ardipithecus ramidus, the 4.4 million year old ‘Ardi’ skeleton described above and another find at Burtele in Ethiopia’s central Afar region indicate that we probably came from a convoluted tree of humans, and that the ostensibly human hallmark of walking upright may have developed more than once. Rigid feet and domed metatarsal heads suggest that Ardi could get around bipedally while on the ground, while her upper body still has features such as fairly long features and arms suggestive of an agile tree climber.
The other find at Burtele also dates to 3.4 million years ago. It consists of only eight small foot bones, but researchers are confident that it represents a new hominim species, and one that was prominently arboreal, despite living at the same time as the bipedal Australopithecus afarensis, (Lucy) a probable direct descendant of ours. This underscores the fact that our status as the only surviving hominim (Neanderthals having gone extinct some 28,000 years ago and the hobbit-like Homo floresiensis about 50,000 years ago) is probably the exception in human evolution rather than the rule, with overlapping forbears cropping up repeatedly[3]. Now that researchers have evidence that two very different hominims – the Burtele species and Lucy – were living at roughly the same time, it is evident that both new and old hominesque fossils will have to be closely re-examined to determine which species they belong to rather than just being assigned to a reigning hominim of that particular era.
Another study has made findings tending to similar effect, namely that nearly two million years ago, homo erectus and his tool-making relative homo habilis (handyman) were probably contemporaries of an even older species called homo rudolfensis, meaning that “human evolution (is) not the straight line that it once was (thought to be)”.
The rudolfensis remains were dug up from sediment dating to the Pleistocene period at a location east of Lake Turkana in northern Kenya between 2007 and 2009. The skull lacked a lower jaw bone. However, within 3 years three other fossils were located within a 10 km radius and found to be attributable to the same species and dated to between 1.78 and 1.95 mya. Scans were used in a virtual reconstruction of the lower jaw, which proved a good fit with upper law of the original find, known as 1470 for short. The findings help to confirm the existence of a distinctive kind of early human nearly 2 million years ago, and not simply a misshapen habilis[4]. The two species probably kept out of each other’s way and ate different foods, the authors of the study surmise.
These themes were taken up by Bernard Wood, a medically trained paleoanthropologist at George Washington University, in an article in Scientific American in 2014[5]. As he says, fifty years ago, tracing the evolutionary ancestors of Homo sapiens was generally thought to be a relatively straightforward matter - from Ardipithecus to Australopithecus (in southern Africa), to Homo erectus (spreading from Asia to Europe) to Homo sapiens, that is, modern humans. In other words, the progression was linear, and each of the various forerunners, were understood to be the direct ancestors of modern humans. Only robust australopithecus was thought to constitute a rather distant relative rather than a direct forebear. It was rather like Darwin’s Tree of Life - with all the species alive today on the outer extremities of the tree and all the species no longer extant near the trunk.
The discoveries of early hominim fossil remains in Olduvai Gorge at sites close to the Eastern Rift Valley in East Africa dating back more than one million years changed that. The fossils in this area have been found in sediments laid down along lakes or along riverbanks. Because they are open air sites, the strata incorporate ash expelled from the many volcanoes generated in and around the eastern Rift valley by the movement of tectonic plates. This gives researchers the means of establishing the age of the strata independent of the fossils they contain, and because they function like “a series of date-stamped blankets” thrown over the region, they allow researchers to correlate fossils deposited thousands of miles apart.
The strata in this cover millions of years of time, meaning that it is possible to give minimum “start” and “finish” dates for each particular group of fossil hominims, signifying that even within East Africa, let alone between east and Southern Africa, there were many times in the past 1-4 million years when more than one and in some periods, several, hominims lived contemporaneously.
For example, from roughly 2.3 million to 1.4 million years ago, a period of about one million years, two very different kinds of hominim, Paranthropus boisei and Homo habilis lived in the same region of East Africa. Therefore, one and perhaps both, were not ancestral to modern human beings. There is also evidence of multiple lineages in our more recent past:
- Neanderthals have been recognised as a separate species for more than 150 years, and as time goes on, researchers discover more and more ways in which they differ from modern human beings.
- We also know that a third hominim, Homo erectus probably survived much later than was originally thought and that H. floresiensis is almost certainly a fourth hominim that lived on the planet within the last 100,000 years.
- Evidence of a 5th hominim, the Denisovans, has come from DNA extracted from a 40,000 year old finger bone. Evidence has also emerged for at least one more “ghost lineage” in the DNA of modern humans from 100,000 years ago.
Thus our recent evolutionary history is much “bushier” than people thought even 10 years ago. In fact one may describe it as more like a bundle of twigs with genetic and fossil evidence revealing that closely related hominin species shared the planet many times in the past few million years, making it more difficult to identify direct ancestors of modern humans than scientists anticipated even 20 years ago.
Another analogy which has recently been utilised is that of a braided stream: “a river that divides into channels, only to merge again downstream". Similarly, the various hominim types that inhabited the landscapes of Africa must at at some point have diverged from a common ancestor, but then further down the river of time, they may have coalasced again, so that we, at the river’s mouth, carry in us today a bit of East Africa, a bit of South Africa and a whole lot of history we have no notion of whatsoever”.[6] Perhaps this should not be thought of as surprising. The same applies to many groups of mammals, so why should hominins have been any different.
Nevertheless, critics of the bushy tree approach have charged that paleoanthropologists have been overzealous in identifying new species from their finds. Wood’s view is that there are sound logical reasons to suspect that the fossil record always underestimates the number of species. Secondly, many uncontested species are difficult to detect using bones and teeth, which is all that survives into the fossil record; and furthermore, most of the mammal species that were living between 3 million and one million years ago have no direct living descendants, and therefore the existence of several contemporary early hominins with no direct living descendants should not appear “odd” at all [7].
[1] Katherine Harmon, “Scattered Ancestry”, Scientific American, February 2013, 36 at 37.
[2] Richard Dawkins, The Greatest Show on Earth, 198. 204-7.
[3] For an illustration, see Appendix 2.
[4] See “Early man not alone, study finds”, SMH, 9 August 2012. The findings were originally published in the Journal Nature. For a depiction of homo rudolfensis, see Appendix 3 from the Smithsonian Exhibition on Life and the Oceans, October 2010.
[5] “Welcome to the family”, September 2014, 27-31.
[6] Jamie Shreeve, "Mystery Man", National Geographic, October 2015, 20 at 56.
[7] Bernard Wood, op cit.
"More like a bush, than a tree"
Source: Smithsonian exhibition on Life and the Oceans (2010), depicting our ancestors over the past 7 million years. Present day humans represent the small bar on the upper line of the diagram, with the now extinct Homo neanderthalensis and Homo floresiensis nearby. The interpolations regarding australopithecus sediba and Homo naledi are my own and should not be relied upon.
Navigation hint: Click on each main-page heading eg "Human evolution - Out of Africa", since material also appears there. Don't just rely on the drop-down menu.
Navigation hint: Click on each main-page heading eg "Human evolution - Out of Africa", since material also appears there. Don't just rely on the drop-down menu.