4. History of Human Evolution
Homo sapiens and chimpanzee, Pan troglodytes have common ancestors, however their lines separated around 5-7 million years ago. Today, Homo sapiens is the only surviving species of the genus Homo. Of the genus Pan, two species are still alive: Pan troglodytes (chimpanzee) and Pan paniscus (bonobo). Along with Pan, Homo belongs to the Hominidae together with gorillas and orang-utans (but not the gibbons, who belong to the Hominoidea).
Over my desk I attached a cartoon that shows side-views of human figures. These walk in increasingly upright positions from left to right with the penultimate man (Homos sapiens) crashing into a hoodie teenager, who stares on his mobile phone. The cartoon is a good persiflage on the smart-phone autism that can be observed everywhere. Another cartoon shows the side views of human figures walking in increasingly upright position until the middle of the image, but then with use of more and more sophisticated tools (spear, jack-hammer) increasingly bent forwards. On the right side of the image modern man sits humpy and writhed in front of a computer. The cartoon is garnished with the remark “somewhere, something went terribly wrong”. Cartoons like that are popular among people, who are interested in science. However, the cartoons described above are not a good description of what human evolution consists of, as it falsely suggests that it was a linear process. In reality evolution is not that straight-forward with each previous type getting replaced by an improved, more upright walking successor. Development lines are probably much more complex and we have to assume that we know only about very few of our predecessors. Likewise, we probably only know few of the successors of the Australopithecus africanus that lived 3,2 million years ago in the High-Plains of East Africa. Apart from the development lines that led to us (Homo sapiens), there surely were a lot of other men-ape like beings, who also emerged from Australopithecus africanus, but who are already extinct by now. We also can not be sure that Homo sapiens really is a succesor of Australopithecus although this is the current view in the textbooks. For us to gain knowledge of a species, several improbable coincidences must come together. Somewhere on earth, an individual of the corresponding species must have died in an environment that favours petrification. Petrification, indeed, has to take place (fossilation) and the fossil has to persist for hundred thousand of years. Through another combination of improbable coincidences, the fossil has to be found by a representative of the species Homo sapiens. Through another combination of improbable coincidences it has to be recognized as important and worth notifying to finally enter the fossil record (16). The formation of fossils from a deceased body that persist over hundreds of thousands of years is always a very rare exceptional case. Normaly the soft tissue organs decay first and the bones remain, but also decomposit over decencies or centuries. Excavations from more recent history may sometimes still contain original body tissues, from which one may be able to isolate DNA. Fossils that are some hundred of thousands of years old, will however be completely petrified, which means that all original tissues and cells have been replaced by minerals. The question to what extent a fossil still contains remains of the original tissue becomes more and more important, as modern molecular genetic methods offer the perspective of isolating and sequencing the DNA of younger fossils (17).
The preservation of fossils in general requires a quick imbedding into air-tight layers, for example through sinking into mud or volcanic ash. Increasing overlaying densifies the sediment layer and pressure and temperature mineralize the body remains (usually the bones). So called “outcrops” are sites, where geological layers of the past surface through erosion, movements of the earth’s crust and faults. Fossils from the corresponding epoche may be embedded in such surfacing layers.
Frequently, fossils of our human ancestors are being found in East Africa and often these fossils were found in the same site, where other important findings were made. Due to the breaking apart of the African continent, (the horn of Africa and parts of East Africa along the long lakes “Lake Tanganyka” and “Lake Malawi” drift apart) the thousand kilometres long Great Rift Valey emerged. Nowhere else in the world have the layers of ancient epochs emerged in such an accessible form and on such a length as in the Great Rift Valey. Maybe our perception of the African origin of man is simply a “detection-artefact” and we only find so many human fossils in Africa, because of the geological conditions that make them particularly accessible in Africa, but not in other parts of the world. However, the high genetic diversity of humans on the African continent supports the hypothesis, that our human ancestors were present on the African continent before they reached other places of the world. Maybe population densities in Africa were higher, so that more human fossils remained and could be found. The numerous human fossils found in Africa paved the way for the ”Out-of Africa hypotheses “, that locate the cradle of mankind on the African continent. I intentionally used the plural ”Out-of Africa hypotheses “. Originally, “Out of Africa” only referd to the expansion of our own species Homo sapiens, who had emerged from predecessors around 200-300,000 years ago in Africa, probably at the horn of Africa and then moved out into the world. As this Homo sapiens migration must have taken place not more than 200-300,000 years ago (Homo sapiens did not exist before that time), this hypothesis is s.t. called „Recent African Origin“ hypothesis, or „Out of Africa II“.
Findings of human fossil on other continents than Africa that are far older than Homo sapiens, leads us to the “Out of Africa I hypothesis”. This hypothesis describes the migration of Homo erectus, of whom around 1.8 million year-old fossils were found in Dnamisi in Southern Georgia in 1991. This is far out of Africa. The distance from Cairo to Tiblisi is around 2700 km. The distance from the East African fossil finding sites to Cairo roughly doubles the distance to Georgia. The findings from Georgia are therefore around 3,000-6,000 km “Out of Africa”. Findings from East Asia, such as the famous Peking Man or the Java Man were allocated to Homo erectus. Homo erectus is considered to be the immediate predecessor species of Homo sapiens. History of human evolution, however reaches further back in time.
About Australopithecus africanus we learned through the Taung child. In 1924, in a chalk querry close to the South African village Taung, the fossilized facial skull of a child was found and presented to the public by an Australian, Raymond Dart. Looking at the traces of injuries on the bones, one can only adumbrate, which tragedy this child suffered. The traces suggest, that a large bird of prey must have gripped deep into the face of its victim. An Australopithecus child of around 10 kg fits into the patterns of prey of such a bird. (Nowadays African Crowned Eagle regularly hunts monkeys in West and Central Africa.) (18).
The Taung fossil, however was not the first finding. The actual dawn of human palaeontology as a discipline rather was the finding of 16 bone fragments, among which was a human calvaria in 1856 in the neander valley (“Neanderthal”) close to Duesseldorf in Germany. Not that there had not been findings of Neanderthal bones before. However, for previous findings in Gibraltar and the Netherlands the importance of the fidnings initially were simply not recognized.
While the age of the Australopithecus Taung child-fossils was estimated to be around 2.4 million years, the bones of the neadnerthales were just around 40,000 years old, thus from a time when Homo sapiens was already present in Europe. The fact that currently we are the only living species of the genus Homo is rather unusual, either. Probably, most of the times, human evolution was driven by a higher diversity of species. Until around 40,000 years ago, at least two Homo-species co-existed in Europe: Homo neanderthalensis and Homo sapiens
Finding the ”Missing Link“, the evolutionary binding link between us and our “predecessor model” or between monkey and human dominated the public perception of the “science of prehistoric primitive man”, but also motivated the palaeontologists themselves. The Missing Link concept, however, is just good enough for cartoons. For evolutionary science itself it is not very helpful as it suggests a linear course of evolution with a predecessor type that is followed by the next better model. Because of the obsession with the Missing Link concept, the value of the Taung fossils was not recognized for a long time. The appearance of the facial skull was closer to monkeys than to humans and the brain was much too small so that according to views held by palaeontologists back then, the Taung child could not have been a predecessor of Homo sapiens. The English palaeontological establishment was obsessed by the idea of finding fossils of human creatures that were as highly-developed as possible with a large brain and kindly had to be from England and not from Germany or even Africa (and not found by an Australian). The findings presented in the year 1912 by Dawson, a real English gentleman was more according to their liking. Eonanthropus dawsoni, the Piltdown man, was found in England and had an impressively big brain. It was key for evolutionary theory-formation in human palaeoantropology for 40 years. Unfortunately, the Piltdonw fossils were forgeries: A detailed investigation in 1953 revealed that the findings consisted of a human skull from the Middle Ages that was merged with the lower jaw of an orang-utan.
New findings of human fossils bear a tendency to proclaim a new species with every discovery. Vanity and the desire for fame and reputation are human weaknesses that also affect scientists. Every finder of a fossil wants the found objects to be important. Ernst Mayer, in the 1950s, appealed to the scientific community to be a bit more conservative, when it comes to proclaiming new species, but rather first make an effort to order new findings into existing taxonomic systems. The tendency to declare a new species for new findings leads to very narrow species-definitions (sensu stricto) with numerous small categories. Ernst Mayr’s approach leads to less, but broader categories (sensu lato). Those, who favour the “sensu stricto” approach are “splitters” as they are splitting the taxonomic tree into more and more branches, while those, who favour the “sensu lato” approach are “lumpers” as they tend to lump together several taxonomic categories. According to this Ernst Mayr was a lumper.
If two individuals in principle are compatible for producing offspring together, they can be seen as belonging to the same species according to one biological definition of species. For palaeontology, where all conclusions are drawn from a few bones and maybe accompanying findings of the environment of the layer, such a definition is not very helpful. Individuals can also be on the same developmental line, but be separated by hundred thousands of years, and if a modern man would be able to reproduce with a woman from 100.000 years ago can not be known.
The history of dicoveries of human fossils that convey nowadays image of the evolution of the hominids is full of personal dramas around ambitious and passionate scientists. However, it is also full of gaps. Species, from which we have not found any fossils remain unknown to us. Furthermore, we can not know, how many species we do not know. Maybe in the future, DNA information from ancestors will allow to genetically define ancestor species, however fossils will remain important as DNA has to be taken from somewhere (a fossil). For old fossils it may be never possible to gain DNA. With fossils that are only a few thousands of years old, DNA-reconstruction has become very successful, but this success becomes smaller, the older the fossils are (17).
When looking for the last common ancestors of human and chimpanzee we will have to rely on the classical, morphological examination of ancient fossils as the corresponding fossils are around 6-7 million years old. In the following I want to recount the history of the humans starting with species from the era, when human and chimpanzee lines split. This history surely has large gaps as the known fossils are only very small islands that are very far from each other in the stream of time.
Some million years ago (5-7) the development lines of humans and chimpanzees separated. However, one should not think of a clear-cut distinction from the human and the chimpanzee line in a magigal separating moment when one child turned to the human and the other to the chimpanzee route. We rather have to assume that the separation process stretched over thousands of years. Especially in the beginning parents from both lines will have mated and reproduced together. The mating between the lines may then have become less frequent and later rare until the two lines became so distinct that parents from each line together could not produce fertile offspring anymore. Probably this incompatibility started with living, but infertile offspring (as can be seen in nowadays mules and hinnies). However, these are all speculations. We simply don’t know. According to current scientific view, the last common ancestor must have lived on the African continent. This would be consistent with the current fossil record. But is it?
Graecopithecus freybergi (Age 7,2 million years, Greece)
The first fossils for this species was a fossilized lower jaw found in 1944 when the Wehrmacht was diging bunkers in Greece, close to Athens. First the finding was classified as a relative of monkeys, later it was allocated to the human line of development. The finding of a 4th premolar (tooth) close to Tschirpan in Bulgaria in 2012 led to a reinvestigation of the stored lower jar and this reinvestigation classified Graecopithecus freybergi as a potential predecessor of the human development line and thus even challenged the Out of Africa hypothesis. Merged premolar teeth are considered typical for the human (Homini) line in contrast to the ape line. The dating of the samples estimated an age of 7.2 million years, thus older than Sahelanthropus, the most ancient pre-human known at that time.
If Graecopithecus freybergi indeed lies on the human development line, the lines of development of humans and chimpanzees must have split earlier than previously thought and the split may have taken place in the Eastern Mediterranean and not in Africa (which challenges the Out of Africa hypothesis)
Before we reject the Out of Africa hypothesis we should however point out, that we have numerous fossils from Africa that still support it and that new findings anywhere in the world can completely change the picture at any time. We speak about millions of years (7 million years), with hundred thousand year long gaps in the fossil record. In these gaps Homini-species can have emerged, spread and decayed without having left traces in the fossil record. Maybe Graecopithecus freybergi is just another evolutionary dead-end street and neiter a predecessor of modern humans nor of modern monkeys. Maybe the taxonomic classification of the fossils is wrong, maybe the age estimate. Unfortunately, it is not possible to gain DNA from such old fossils and all conlusions and speculations must be based on morphology, layer and layer environment at the finding site
Sahelanthropus tchadensis (6-7 million years, Chad)
The relatively well conserved skull that serves as a holotype for this species was found on the surface in lose sand. This makes one of the most important method for age estimation and contextualization difficult as no geological layer can be allocated. The age was roughly estimated at 6-7 million years old. Thus, Sahelanthropus tchadensis could have lived before, during or after the last common ancestor of humans and chimpanzees or even be it. We simply can not know. It could also be on a diffent line, maybe the one leading to gorillas, maybe a dead-end line. Keeping in mind that we know about several extinct homini species from a closer past (e.g. the Neandertals or the Denisovians) and with a far better fossil record the dead end line may be a very common destiny of many ancient species, for which fossils were found, so possibly also for Sahelanthropus tchadensis.
Ororin tugenensis (6 million years, Kenya)
Findings from a site in the Tugen-hills, 250 km west of Nairobi were classified as O. tugenensis. Alread in 1974 a molar tooth of a prehistoric man/ape was found, but not before the years 2000, when two pieces of a lower jaw bone with 3 molars and five lose teeth, two finger bones and a piece of a humerus and a femur bone added to the species’ fossil record, was it perceived as spectacular. Sometimes O. tugenensis is called the millenium man. The fossils are around 6 million years old, but were found in different geological layers suggesting that their age may be even hundreds of thousands of years apart from each other. The conclusions drawn from the findings, that this is one species that lies in a direct line of development to modern humans, thus making Kenya the cradle of mankind are quite brave, to say the least.
Ardipithecus kadabba (5.6 million years, Afar Depression, Ethiopia)
First the fossil-findings made between 1992 and 2001 in the Ethiopian Afar Depression were allocated to the around one million years younger Ardipithecus ramidus, however new findings in 2002 led to the establishment of Ardipithecus kadabba as a species by itself. It was described as sharing more features with Sahelanthropus and Ororin than with later Ardipithecus. Its allocation to the Homini line is disputed.
Ardipithecus ramidus (4,4 million years, Afar Triangle, Ethiopia)
In october 2009 Ardipithecus ramidus bones arranged in their anatomical order to a complete skeleton were shown on the cover of the renowned scientific journal “Science”. The fact that enough bones of this species were available for arranging them to a roughly recognicable skeleton gives us a good imagination, how Ardipithecus ramidus could have looked like. Sometimes Ardipithecus ramidus is even considered as a good candidate for being the last common ancestor of human and chimpanzee.
Altghough the long arms point towards “Ardi” having been tree dwelling, elaborate examinations of foot and pelvis bones (e.g. with computertomographs) found indication for an upright walk. The walking foot had opposable big toes that allowed to grip with the foot. Together with the long arms this points towards a life in the trees. The bones of hands and forearms suggest that the hands of Ardipithecus ramidus were less rigid and stable than the hands of nowadays chimpanzees and gorillas. One can thus assume that they made less use of the knuckle-walk and may (often) have walked on two feet. This may have deliberated the hands to do other things.
However, we can not apply the linear model of evolutionary progress only to make us the crown of the evolution. Regarding locomotion we have a tendency to perceive the bipedal walk as being more progressive than the quadruple knuckle-walk. But maybe for the chimpanzees and the gorillas the knuckle walk was simply the better model. Maybe the last common ancestor had already a strong tendency to walk upright, but for chimpanzees the quadruple mode of locomotion was simply better. Leg injuries can surely be better compensated if an animal walks on four limps rather than on two. Since the last common ancestor, chimpanzees also underwent 6-7 million years of evolution and have adapted to the needs of their species.
The excavations that brought up the fossils of Ardipithecus ramidus also found thousands of other fossils from animals and plants: rodents, monkeys, hyaena, elefants, birds, but also fossilized woods and plant seeds. The contextualization of the findings fits to a species-diverse forrest habitat comparable to nowadays rainforests. If Ardipithecus ramidus is considered as a predecessor of humans, the view that the human line developed in a savannah environment is being challenged by these findings. The brain volume of Ardipithecus ramidus was around 300-350 cm2 and thus smaller than the brain of a chimpanzee.
Currently 5 species are allocated to the genus Australopithecus:
- anamensis (4.2-3.9 million years, East Africa)
- afarensis (3.8-2.9 million years, East Africa, Lucy!)
- africanus (3.0-2.1 million years, South Africa, Taung-child!)
- garhi (2.5 million years, Ethiopia)
- sediba (1.95-1.78 million years, South Africa )
Sometime Kenyaanthropus platyops (3.5-3.3 million years, Lake Turkana, Kenya) is also considered among the Australopithecines. Up to now, only a completely broken skull of this species has been found and the morphological impression given by the reassembled skull may be wrong. Some palaeontologists critisize that for a finding of such a bad quality, no new genus should have been declared (Kenyaanthropus) and the debris of the skull may well belong to an already known genus and species (e.g. A. afarensis).
The Genus Paranthropus
The Genus Paranthropus is considered to be a parallel line of the Australopithecines and the early Hominids, however the distinction from the Australopithecines is disputed, this is why we face two different taxonomic names for each same species:
Australopithecus aethiopicus is P. aethiopicus (2.8-2.3 million years),
Australopithecus boisei is P. boisei (2,3-1,4 million years) and
Australopithecus robustus is P. robustus (2,0-1,5 million years)
If considered as a genus by itself or as species of the genus Autralopithecus – all three „Paranthropines“ were allocated to an extinct side line and are thus not seen as ancestors of Homo sapiens.
Australopithecus anamensis (4.2-3.9 million years, East Africa)
- anamensis is the oldest representative of the genus Australopithecus. Its lower jaws resemple those of nowadays chimpanzees, however the teeths look rather hominid (smaller). The fossil-findings reach from Lake Turkana region northwards to Northern Ethiopia. Most findings were around Lake Turkana, a region with high volcanic activities with frequent volcanic explosions in the lifetime of A. anamensis. Fossils of victims of such natural disasters were found between a 4.35 million years old basaltic flow layer and a 3.89 million years old tuff layer (rock of volcanic ashes). Maybe the younger species A. afarensis emerged directly from A. anamensis.
Australopithecus afarensis (3.8-2.9 million years, East Africa, Lucy!)
The more than 900 A. afarensis fossil findings cover the same area from Northern Ethiopia to Northern Kenya as those of A. anamensis, but reach further South down to Southern Tansania. Possibly A. afarensis indeed emerged by anagenesis (gradual evolution with further development) from A. anamensis. The cartoonish image of side views of human figures walking in increasingly upright position may be justified in this case.
In Novembre 2013, I escaped from a conference in Addis Abeba for an afternoon in order to see an ancient superstar: Lucy! She just had returned from America to her place in the Ethiopian National Museum. As I later found out, the exposed bones were only copies. Since her return, the originals were kept in a safe. Nevertheless, already the copy of the skeleton triggers awe. The simple glass chest is a funeral site and a memorial of one of our most famous ancestors. With Lucy, a popular star originated from Australopithecus afarensis. Due to the assumed sexual dimorphism in A. afarensis, the skeleton found in 1974 in Hadar in North Eastern Ethiopia, probably seemed to be female and not fully-grown, yet. In 2006 a very well preserved, 3.3 million years old A. afarensis skull of a small child was found in the Afar Triangle of Ethiopia. The palaentologists named the child “Salem” (peace), but soon the nick name “Lucy’s Baby” emerged.
Many important A. afarensis fossils were found in Laetoli, around 50 km south of the Tanzanian Olduvai-Gorge, which is known for many human fossil findings. The famous Laetoli footprints were from buffaloes, antilopes, baboons, pigs, hyenae, and from 2 upright walking, bipedal walking beings with human-like feet. Probably these two A. afarensis were walking through still wet and soft volcanic ashes of the volcanoe Sadiman. A. afarensis walked upright on the ground, but still had the long arms that are typical for tree-dwelling organisms. The teeth were larger than human teeth, but smaller than monkey teeth. The upright walking posture apparently developed long before the emergence of larger brains (the brain of A. afarensis is about 1/3 of the size of our brain).
Australopithecus africanus (3.0-2.1 million years, South Africa)
The already mentioned Taung-child, whose skull was found in South Africa in 1924 around 400 km west of Johannesburg, was the first fossil finding of early humans in Africa. The genus term „Australopithecus“ (Southern Ape) was coined back then. As described above the Taung-child apparently was victim of an eagle attack, which shows that Australopithecus was somewhere in the middle of the food chain and thus frequently became prey. The brain of A. africanus is somehow larger than that of A. afarensis and the teeth a bit smaller. Further findings were made in Sterfontein, North-East of Johannesburg, among which a 2.1 million years old skull that shows that the species A. africanus still existed at that time. Numerous teeth of A. africanus were found in the Gladysvale cave close by and seem to indicate that A. africanus was a plant eater.
Australopithecus garhi (around 2.5 million years ago, Ethiopia)
The type specimen of A. garhi consists of a skull with upper jaw facial fragments and large molar teeths and was found in 1997 in the Afar Triangle of Ethiopia close to the village Aramis. Meanwhile other Australopithecus bones were found in the surroundings of the type specimen and allocated to A. garhi, although one can not be sure that they do not belong to another Australopithecus species. If the bone allocation is correct, A. garhi has long arms just as the other Australopithecines and a brain size of around 1/3 of ours. Compared to other Australopithecines the femur bone is longer. In the surroundings of the findings, animal bones with scratch traces were found, possibly indicating the use of tools. Based on other animal and plant fossils, the habitat of A. garhi was described as a savannah-habitat with freshwater lakes. This is in contrast to the habitat of A. afarensis who is thought to have dwelled in thick forests. Longer femur bones could have been an adaptation of A. garhi to the open landscape.
Australopithecus sediba (1.95-1.78 million years, South Africa)
In 2008 in the Malapa cave close to Johannesburg in South Africa, two complete skeletons were found, whose pelvis resembled those of the genus Homo. The overall habitus and the small skull of 420 cm2, however, was more compatible with the genus Australopithecus.
Australopithecus bahrelghazali (3.5-3.0 million years, Chad)
In 1995, a lower jaw was found close to Koro Toro in Chad. The time allocation as the allocation to the genus Australopithecus are disputed. If A. bahrelghazali indeed was an Australopithecus the presence of Australopithecus in Western Africa would have been demonstrated
If we accept the allocation of Homo rudolfensis and Homo habilis into the genus Homo, their 2.5- to 1.5-million-year-old fossil findings are the oldest remains of the genus. When regarding evolutionary processes as rather continuous than stepwise, the distinction between hominids and australopithecines is rather artificial anyway and only a matter of definitions (of genus). It certainly would be interesting to look at the biologigal boundaries between species. Taking the classical definition of species, one wanted to know if a man and a woman are in principle able to produce fertile offspring and to what extent this happened between species defined along morphological classifications through palaeontologists. Finding out about this seems impossible for the older hominids as behavioural information and information about interactions can hardly be gained from the few findings of fossils. At best, grouped fossil findings pointing for example towards family cohesions could allow for some highly speculative assumptions. From ancient, completely mineralized fossils, no DNA can be gained, so that information from million of years old fossils consist of morphological comparisons of bones, geological layer and age definition and artefarcts embedded in the same layer close to each other.
Around 2 million years ago, Homo rudolfensis, Homo habilis and Homo erectus lived as contemporaries on the earth. To what extent they had encounters can hardly be deduced from the overall few fossils and the imprecision regarding estimates of time. Fossila from all three species wer found in East Africa, so that one can at least assume that geographical proximity with possible overlap of living areas and habitats was given. Did these three human species produce (fertile) offspring together? Is one of these species, or are these species direct predecessor in the line to Homo sapiens?
Unfortunately, the fossils are too old for counting on the possibility to one day isolate their DNA in order to elucidate their genetic relations. And, there is a huge fossil gap in the decisive period of human development around 2-3 million years ago. Between the fossils of A. afarensis (Lucy, around 3 million years ago) and fossils of the first hominids, which were (interestingly) found in close areas of Ethiopia, yawns a gap of 500-750,000 years (19).
Half a jaw bone with embeded molar teeths was recently found in the Afar region of Ethiopia. It shows characteristics of Homo lower jaws and was dated to be around 2.8 million years old making it an important Island in the wide fossil gap between Australopithecus and Homo.
Excursus: Species of the genus Homo, who were not contemporaries of Homo sapiens (Homo rudolfensis, Homo habilis, Homo ergaster)
Homo rudolfensis (2.5-1.5 million years, Kenya, Ethiopia, Malawi)
- rudolfensis is the first representative of the genus Homo. According to the age estimation of its oldest fossil representative (a lower jaw bone from Malawi), H. rudolfensis already lived 2.5 million years ago and thus was a contemporary of the late Australopithecines. Timely overlaps would have consisted with A. africanus (3.0-2.1 million years ago), A. sediba (1.95-1.78 million years ago) and possibly with A. garhi (2.5 million years ago). In 1975, Lake Turkana was renamed according to the ethnic group of the Turkana people living there. Before its renaming it was named “Rudolfsee” in honour of the prince-royal of Austria-Hungary in the 19th century.
The type specimen of H. rudolfensis, a skullbone without jawbone and teeth was found in 1972, before the renaming of the lake and dated to be around 1.9 million years old. More findings were made in Ethiopia (close to the Omo river that flows into Lake Turkana) and in Malawi. The 2.5 million years old lower jaw bone found in Malawi, demonstrated the existence of the species H. rudolfensis in more ancient times, when Australopithecines still roamed.
Morphologically H. rudolfensis has features of a transitional species between Australopithecines and Hominids. There also were claims that the typus specimen from Lake Turkana could be from a representative of the species Kenyananthropus platyops. As described above, Kenyananthropus platyops is only defined by a skull that was entirely broken up into pieces and could have been reassembled incorrectly thus giving a wrong morphological picture. Consequently, one could ask, if the “K. platyops debris“ skull could not belong to another Australopithecus or to H. rudolfensis.
However, it is also disputed, if H. rudolfensis is a species by itself, or if its fossils could be allocated to other Australopithecines and Homo species (H. habilis or H. errectus). The large brain volume of 750 cm3 speaks for the genus Homo. Unfortunately, from fossils as old as these, no DNA can be isolated, which would shed light onto the phylogenetic trees. All allocations of million years old fossils into species build on comparisons of bone morphology and age estimates of the findings.
Homo habilis (2.1-1.5 million years, Tanzania, Kenya, Ethiopia, South Africa)
Even Homo habilis is not without any doubt allocated to the genus Homo. “Habilis” means skillful and refers to the numerous stone tools of the Oldowan type found in layers that were allocated to H. habilis (deduced from the Olduvai Gorge in Tanzania, where such tools have been found first). The Oldowan type tools were processed stones that are commonly refered to as hand-axes. These tools were used for striking and grinding functions, which would however not mandatorily require a previous treatment of the stone. The Oldowan type tools were blunt and tangible on one side, but sharp on the other, so we can assume that they were also used for scraping, rasping and cutting. Probably, Homo habilis could open and process animal carcasses. This would mean that H. habilis did not need to open the carcasses with their teeth. This could have triggered a degeneration of the human denture (finer teeth and no more fangs). This degeneration went so far, that modern humans would hardly be able to open an antelope carcass with their teeth. The opening of bones could have been of particular importance, as it allowed to suck the bone marrow. For small hominids, who were somewhere in the middle of the food chain, the bone marrow could have been an important source of protein. Some even think that the bone marrow could have been the decisive protein source for triggering our brain development.
Apparently, Australopithecines already opened bones, at least if 3.5 million old traces on bones from the Afar region in Ethiopia indicate this (20). Unfortunately, the fossil record for H. habilis is feeble. If H. habilis is supposed to be the bridge between the Australopithecines and representatives of the genus Homo, this bridge is very thin, fragmentary and fragile.
Homo ergaster (1.9-1.4 million years, South and East Africa)
According to the current view, Homo ergaster emerged from H. rudolfensis. According to the age estimates of the fossil findings from South- and East Africa, H. ergaster lived around 1.9-1.4 million of years ago and thus was contemporary of H. habilis and Paranthropus/Australopithecus boisei. Prominent representative of the species Homo ergaster is the “Turkana Boy”, a nearly 1.6 million years old nearly complete skeleton (only hand and foot bones were missing) of an 8–12-year-old boy, which had been found in 1984 at Lake Turkana in Kenya.
Many H. ergaster fossils stem from beings, who were younger than 14 years old, which indicates an in average rather short live expectancy. Together with H. ergaster fossils, processed stone artefacts are commonly found, indicating a certain ability to handle and manipulate tools and objects. Furthermore, it is reckoned that Homo ergaster used fire.
Possibly, H. ergaster was the African variant of Homo erectus. According to the Out of Africa hypothesis I, Homo erectus was the first human species to spread out from Africa opening up habitats in Eurasia. Most palaeoanthropologists view Homo ergaster as the African Homo erectus. Some representatives of H. ergaster may have moved out into the world, where they left fossils that were named and allocated to H. erectus.
Homo erectus (1.9 million – 70.000 years ago)
According to current knowledge, H. erectus was the first human species, that moved out of Africa and opened up living habitats on the Eurasian continent (Out of Africa I). The lumpers integrate a vast number of fossil findings from a time span of nearly 2 million years into the species H. erectus (Table 2). If an H. erectus gentleman living 1.5 million years ago would have been able to reproduce with a H. erectus lady living only 200.000 years ago (thus fulfilling the biological definition of a species) may be doubted. Due to the global expansion and the long-time span of 2 million years, we may assume that genetic changes over time and in different subpopulations (geneshifts, mutations, selections, recombinations) may have given rise to different (sub-)species of H. erectus. The global expansion of such subspecies was also separated geographically favouring allopatric speciation, which is favoured if two population of the originally same species were separated over a long time.
Homo erectus subspecies (21)
Age estimates of the findings (years)
H. erectus erectus (1)
Solo river, East Java
1,66 – 0,9 million (or 0,14 million.?)
H. erectus yuanmouensis (2)
Yunnan province, China
H. erectus lantianensis (3)
Shaanx province, China
H. erectus nankinensis (4)
Jiangsu province, China
H. erectus pekinensis (5)
H. erectus palaeojavanicus (6)
H. erectus soloensis (7)
Java (Solo river)
H. erectus tautalevensis (8)
H. erectus georgicus (9)
- Tautavel Man
If recent age estimates of Homo erectus fossils from the Solo river in Ngandong (Java) are correct, Homo errectus lived until 140,000 years ago, possibly even until 70,000 years ago (21), which would mean that H. erectus lived in parallel as a contemporary of H. sapiens. However, the age estimate of such river-washed ashore fossils has to be handled with care. The wide distribution of Homo erectus made some palaeontologists question the twofold Out of Africa hypothesis, according to which 1.8 million years ago, humans of the species Homo erectus left the African continent and spread over Eurasia (Out of Africa I), and later around 60-70,000 years ago Homo sapiens left the African continent and spread over Eurasia (Out of Africa II)
An alternative hypothesis is that of continuation of evolutionary lines of widely distributed different H. erectus (sub-)species to H. sapiens in different places of the world. Nowadays’ East Asians would then be successors of East Asian H. erectus instead of having emerged from a new wave of H. sapiens from Africa according to Out of Africa II. This theory, however, requires that no allopatric speciation with formation of distinct species over time had taken place. Therefore this “theory of multiregional evolution of humans” is supported only by a minority of palaeontologists. Furthermore, genome comparisons that and universal ability to reproduce with each other, makes the “theory of multiregional evolution of humans” appear unlikely. More likely is the view, that the H. erectus fossils of East Asia originate from extinct species, thus wiped-out lines of human evolution and that Homo sapiens indeed emigrated from Africa and spread all over the world (Out of Africa II).
Homo naledi (0.3 million years ago)
First, the findings that were made in 2013 in the Rising Star cave in South Africa, were thought to be from the transition period between Australopithecus and Homo, due to rather archaically seeming morphological features and the small body size. The age estimate of the fossils revealed a surprisingly young age of only around 300,000 years (22). This suggests that H. naledi lived rather shortly before or even as a contemporary of early H. sapiens. If H. naledi is a species by itself, or rather has to be allocated to one of the existing species (or genus) such as Homo erectus, is under debate.
Homo heidelbergensis (0.7-0.2 million years)
Originally H. heidelbergensis findings in Europe were allocated to the line between H. erectus and H. neanderthalensis. Most H. heidelbergensis findings were made in Northern climate zones, which during lifetime of the species were colder than most habitats, where human species developed. Findings of H. heidelbergensis fossils made in Africa (H. rhodesiensis), India and China suggest that H. heidelbergensis lies on a common line from H. erectus to the modern man H. sapiens and to H. neanderthalensis.
In the open brown coal pit of Schöningen between Lower-Saxony and Saxony-Anhalt, spears and tools were found that indicate that H. heidelbergensis hunted large animals (horses, wisents, forest elefants). It is assumed that H. heidelbergensis was capable to build shelters from wood and leaves and mastered fire.
Homo antecessor (780.000 years)
If Homo antecessor is a species by itself or if the corresponding findings should be classified as early Homo heidelbergensis is still disputed. The first H. antecessor fossils were found in 1976 in Atapuerca in Northern Spain in a cave named “Sima de los Huesos” (bone pit). Systematic excavations in the „Gran Dolina“ cave nearby revealed more Homo and animal fossils. These findings in Spain demonstrated an earlier presence of humans in Europe than was anticipated at that time. Scratch and cut marks on H.antecessor bones were asumed to be signs of cannibalism (23).
Depending on different points of view, the existence of Homo sapiens is estimated to be around 200-300,000 years. The further we expand this time into the past, the weaker the explanatory power of fossils becomes. With completely mineralized fossils, one can only draw conclusions from morphological features, the layer of the findings and maybe from artefacts found in the vicinity of the fossil. From newer maybe only a few ten-thousand-year-old bones, it is nowadays possible to extract DNA and thus gain genetic information allowing for genetic comparisons. This has already been successfully done for the famous Neanderthal, more about this later (24).
There is a lot of insecurity on until when H. erectus was roaming the earth. The presumably youngest H. erectus fossils were found washed-up in the Solo river in Java and are hard to age-date as several layers were mixed up. Furthermore H. erectus is such a wide species category, containing so many different fossils from different times and places that it is always questionable, which fossils are still correctly classified as H. erectus or if other species (e.g. H. heidelbergensis) would be correct. Nevertheless, it seems likely that early generations of Homo sapiens were contemporaries of the species (or the many species?) Homo erectus. Homo sapiens probably emerged from the African Homo erectus, so one could maybe rather consider a species overlap than a parallel existence. To what extet the genome of the modern H. sapiens contains DNA of H. erectus is (yet) unknown as H. erectus DNA could not be isolated, yet.
However, without considering H. erectus, it is still sure that there were other human species during lifetime of H. sapiens. Today, H. sapiens is the only representative of the genus Homo, but only 30,000 years ago there were other human species. For the last hundred thousand years, we know of the Neanderthal (until around 30,000 years ago), the Denisovan, (until around 60,000 years ago) and the Flores Man (Homo floresiensis, “Hobbit”; until around 60,000 years ago or even only 18,000 years ago).
Island locations bring about unique evolutionary developments with Island-specific habitats and ecosystems, sometimes with endemic species that occur nowhere else in the world. We may want to think of the iguanas of the Galapagos islands or of the lemurs in Madagascar, who are a suborder of the primates and uniquely live in Madagascar (order > family > genus > species). Out of the Hominidae family in the genus Homo, Homo floresiensis, may also have been an endemic Island species, which due to the remoteness of the Island emerged with its very own features. When in 2003, a small skull was found on the Indonesian Island of Flores that had features of a small human, but whose denture just did not fit to a child, the excitement among palaeontologists was huge. The small H. floresiensis was sometimes nicknamed “Hobbit“, a reference to the fantasy-novels of the British writer Tolkien.
While cold-blooded animals tend to become bigger on Islands (Island-gigantism – think of the Galapagos tortoise), larger mammals living for generations on an Island without any connection to mainland populations, tend to become smaller over generations (Island dwarfism – visible on Island populations of elefants or buffaloes).
Age determination of H. floresiensis fossils revealed quite recent dates (the closest estimate being 12,000 years), however the currently best accepted estimate is rather 50-60.000 years (25). Essays to gain DNA remained unsuccessfull up to now. New hope lies in the isolation of collagen proteins preserved in teeths and the determination of their amino-acid sequences (26).
The more recent the time when H. floresiensis became extinct, the higher the probability of encounters with H. sapiens. In principle such encounters could have been prevented by the remote Island location, at least if Flores was the only habitat of H. floresiensis. How possible contacts played out and if H. floresiensis and H. sapiens may perhaps have reproduced and left common offspring is speculative. Maybe there were encounters with other species (H. erectus, H. sapiens) that took a fatal course (27, 28). With regards to the again and again resurfacing genocidal tendencies of H. sapiens, a violent eradication of H. floresiensis by other Homo species is conceivable. Without any doubt, the isolation of DNA from H. floresiensis would be a scientific breakthrough.
While H. sapiens thrived in Africa, South- Middle- and Eastern-Europe were Neanderthal-land. During the last ice age from around 110,000 to 12,000 years ago, large parts of Northern Eurasia down to Northern Germany were permanently covered with glaciers. As large amounts of water were bound in land-ice, the sea level worldwide was lower leaving landbridges between the continents, which also were wider. This favoured the distribution of land animals such as H. sapiens.
Encounters of H. sapiens and H. neanderthalensis (who became extinct 30-40,000 years ago) can be regarded as ascertained. How these encounters played out, if peaceful or violent, if the species avoided each other or sought social interaction, allows for speculations and fascinating discussions. However, the uncomfortable question remains, why we still are, but the Neanderthals are extinct.
- erectus, (who in a first distribution wave spread over Eurasia – Out of Africa I) is viewed as a common ancestor from whom H. sapiens and H. neanderthalensis branched off around 700,000 years ago and had developed two different (Sub-)species. The spatial separation (H. sapiens in Africa and H. neanderthalensis in Europe) favoured the allopatric (Sub-)species formation. H. heidelbergensis could have been a direct predecessor of the Neanderthal. From H. heidelbergensis numerous fossils have been found in Africa and some palaeontologist postulate that H. heidelbergensis could be a common ancestor of H. sapiens and H. neanderthalensis.
Compared to H. sapiens, Neanderthals were a bit smaller, but sturdier and compact in posture. They had prominent supraorbital ridges and a more massive skull with a slightly larger inner skull volume and, consequently, a slightly larger brain volume than H. sapiens. Just as H. sapiens, Neanderthals used tools, controlled fire and buried their deceased. Fossil findings of Neanderthals stretch from Gibraltar all over Europe to Western Siberia. Neanderthals lived in Eurasia, but not in Africa. In the human Homo sapiens genome of Non-Africans 2-4% Neanderthal sequences can be found (17).
Around 30-40.000 years ago the Neaderthals vanished. In the following, I will list and discuss theories refering to the extinction of H. neanderthalensis. However, I do not claim that one single theory should be sought as the exclusive explanation for the disappearance of the Neanderthals, rather each theory should be seen as a factor that could have contributed more or less to the extinction of the Neanderthals. With some of the theories, one should question the occasionally postulated superiority of H. sapiens and even if this superiority was given, how it translated into reproductive superiority. (The superiority claim for H. sapiens should be questioned anyway. Remember that Neanderthals had larger brains than us!). A cognitive superiority, for example, does not mandatorily mean that the cognitive inferiors reproduce less successful. In this context one may remember that in many H. sapiens cultures intelligent or well-educated people intentionally abstain from reproducing. Think of monasticism or of childless philosophers and scientists, who invest the time they gained by having no childcare obligations into their philosophical or scientific work. Certainly, one can not draw conclusions from modern developed societies to the conditions in hunter-gatherer societies.
Neanderthals had a larger brain than Homo sapiens. When looking for reasons for the Neanderthal’s extinction, we tend to look for properties of the Neanderthals, that make them look inferior to H. sapiens. This may not be right. The only inferiority that really matters in this context is reproductive inferiority. Why did Neanderthal populations shrink from generation to generation, while H. sapiens populations grew?
1. Homo sapiens violently replaced Homo neanderthalensis (genocide, species-homicide)
The history of Homo sapiens is full of examples of violent wars of submission and genocides. Modern empires are based on military power. The idea, that our ancestors massacred the Neanderthals and replaced them in their habitats does not seem far-fetched. If H. sapiens hunted large animals, violence and killing was well established in the behavioural repertoire and inhibitions against killings were low. If the Neanderthals on the other hand had mainly gathered eatable plants as some palaeontologists postulate for the Neanderthals that lived in nowadays Spain (29), violence may have been less common. Thus, the Neanderthals would simply have been too peaceful for the confrontation with our aggressive species and were massacred and violently exterminated.
2. Volcanic Erruptions
The Campi Flegrei super-volcanoe close to nowadays Naples, errupted around 39,000 years ago and led to sun-darkening through ashes for several months in South-Eastern Europe, Levantine, the Middle East and Central Asia, all regions inhabitated by Neanderthals. Homo sapiens had a solid population basis in Africa and could replace the populations that died due to the volcanic eruption. Possibly the Neanderthals could not compensate for the large losses and died out. The youngest findings of Neanderthal-fossils were made in Gibraltar, the extreme South-Western tip of Europe that was spared from the ash-clouds. Maybe, here the last surviving Neanderthal-populations lived, but were then demographically replaced by Homo sapiens or mixed with (larger) H. sapiens populations and were absorbed. Around 2-4% of the genome of Non-African people consists of Neanderthal-sequences (17).
3. Homo sapiens domesticated Animals and cooperated with Wolfs when hunting
Findings from Belgium demonstrated that the Northern Neanderthals, in contrary to those living in nowaday’s spain, heavily relied on large animals such as mouflons and wooly rhinoceroses (29).
Around 40.000 years ago, the three top predator-species in Europe were Homo sapiens, Homo neanderthalensis and wolfs. An alliance with cooperative hunting of two of these top predators may have brought about a decisive competitive advantage in the competition for animals. The close relations of our ancestors to wolves is reflected by us still holding on to dogs, who evolved from wolves. The start of the domestication of the wolf through Homo sapiens (and the emergence of numerous dog species) is estimated to have taken place around 40,000 years ago, the time when Neandterhals disappeared (30). Today’s sniffer dogs remind us that wolves may have helped to find animals and track them down. Wolves hunt in packs, can encircle large animals and drive them to the humans, who then kill them using their spears and axes. A cooperation with wolves would also have served to drive off other carion eaters (31).
4. Homo sapiens could have been more skillful Hunters
The disappearing of the Neanderthals correlates with the arrival of Homo sapiens in the Neanderthals’ Eurasian habitats. Maybe there was direct competition between H. sapiens and H. neanderthalensis and Homo sapiens prevailed because of better hunting-techniques and thus was able to nourish more people.
5. Sharing of Tasks between Sexes and Age groups may have made the Organisation of Homo sapiens Groups more efficient than those of the Neanderthals
Neanderthals probably hunted in family groups with all family members, including women and children contributing to the hunt. H. sapiens may have developed a more sophisticated task sharing depending on age and sex that allowed the individual to take on tasks that were best suited to individual abilities and restrictions. Task sharing made the overall processes more efficient. While strong young men hunted a large animal, women and the elderly already made preparations in the camp for the later processing of the animals. Heating meat made it better digestible and exploitable. This required the mastering of fire, which may be easier in a society with shared tasks. However, Neanderthals may also have had elaborate task-sharing and social organization structures (32).
6. Neanderthals could have had lower Cognitive Abilities
Neanderthals had a larger internal-skull volume than Homo sapiens. Possibly, the Neanderthals were even cognitively superior to Homo sapiens. Maybe the brains of the Neanderthals had a completely different structure that was inferior to that of the H. sapiens at least regarding cognitive functions that are important for survival and reproduction. Compared to the steep frontal part of our skull, the frontal skull of the H. neanderthalensis appears rather flattened. The frontal lobe of the Homo sapiens brain processes social behaviour, creativity, abstract thinking. Maybe this made Homo sapiens the better learner and teacher or brought about a stronger social cohesion. This may have helped to spread advantageous technologies and insights did not have to be made by each individual as experience and knowledge could be passed on efficiently by explanation.
7. Homo sapiens collective Believe in Non-objectiviable Entities could have brought about an Advantage for achieving Common Goals
After the discovery of the Neanderthal fossils in 1856 it was taken as self-evident that the fossils originated from a primitive cave man, that could under no circumstances match the cognitive and cultural abilities of Homo sapiens. Meanwhile, this assumed superiority of H. sapiens is under serious doubt. In the current discourse a cultural superiority is hypothesized. According to this H. sapiens groups could have had a higher level of cultural organisation (33). Even if the individual Neanderthal had been cognitively superior (larger brain volume), the culture associated tendency to believe in non-objectiviable entities and institutions (religion, “spirit of the group”, supernatural mission) could have been the decisive factor in the competition between H. sapiens and H. neanderthalensis (34). Common culture can help for pursuing common goals and create cohesion in larger groups without them being genetically related. Even people who do not know each other can be made to cooperate, for example in warfare, if they are given a common goal. Maybe our H. sapiens ancestors were simply more susceptible for propaganda and enemy images making them mobilizable for military operations such as killing peaceful Neanderthals.
- The Neanderthals could have been more conscientous and could have had stronger inhibitions to kill
Without any doubt, the Neanderthals had larger brain than us. It will never be possible to assess, if H. neanderthalensis or H. sapiens, had better cognitive abilities. Many higher developed mammals (among which humans) have a strong inhibition to kill fellow humans. This inhibition to kill can well be substantiated through high cognitive abilities, a highly developed, conscientious mind, for example. However, especially in humans we often see failure this inhibition to kill. Even more importantly, our inhibition to kill is being intentionally canceled (war propaganda, weapons that facilitated the killing and that lower the threshold to kill). In violent conflicts, inhibitions can be a disadvantage and the disinhibited less conscientious party may prevail. In our case the disinhibited Homo sapiens would have prevailed over the conscientious Neanderthal.
9. Weather and Climate changes in the habitats of the Neanderthals
When Homos sapiens emigrated from Africa, he first populated the Arabian Peninsula (around 100,000 years ago), then Central Asia (around 70,000 years ago) and finally Australia (around 60,000 years ago). According to this, Homos sapiens populated distant Australia even before Europe, where he emerged around 40,000 years ago. Possibly, Homos sapiens populated Europe not before the decline of the Neanderthals. Another possible explanation for the extinction of the Neanderthals may be in drastic weather and climate changes with changes of habitats. If for example cold forrest habitats were replaced by warmer, more open savannah habitats, the conditions may have favoured Homo sapiens over the Neanderthals. Homo sapiens developed in the open savannahs of Africa and may have been attracted to the opening landscapes of European habitats.
10. Neanderthales could have become Victims of Plagues
Homo sapiens could have imported microorganisms, that flourished in the bodies of H. neanderthalensis because of the evolutionary proximity of these two human species. The Neanderthals’ immune system had no previous exposure to these microorganisms, which may have been fatal for the Neanderthals. They may have been killed by microorganisms that were relatively harmless for H. sapiens (35). This explanation looks plausible. There are historical examples of plagues in peoples who get in touch with other peoples for the first time. We have to assume that the Europeans, who invaded America in the 16th and 17th century imported infectious diseases that were entirely new to the immune systems of the indigenous people (36). Probably, the mass dying among native Americans, of whom only and estimated 5% survided with whole tribes and peoples dying out, was mainly due to plagues (37). Neanderthals could have suffered a similar destiny.
11. Inbreeding was very common among Neanderthals and hampered Fertility
Possibly, Neanderthals lacked healthy and fertile offspring due to inbreeding. Humans have 46 chromosomes, 23 from their mother and 23 from their father. Crossing-over assures some genetic exchange between maternal and paternal chromosomes, so that each individual has chromosomes with a unique character. The difference between maternal and paternal chromosomes can be examined and in population genetics the “heterozygosity” quantifies the ratio of observed to expected frequency of differences. When comparing maternal and paternal chromosomes, differences are stronger in Homo sapiens than in Neanderthals, where some maternal chromosome segments are nearly identical to corresponding paternal chromosome segments. Such agreements of parental chromosomes are and indicator for the degree of relatedness of the parents. DNA sequences from a toe bone of a Neanderthal woman from the Altai mountains, indicated high degrees of relatedness of the parents. Different plausible constellations of relatedness were half siblings, uncle-niece, aunt-nephew, grandparent-grandchild, double first cousin (offspring of two sibblings who mated with sibblings) (38). The level of agreement of maternal and paternal chromosomes suggests that reproduction between relatives were very common also among the predecessor generations of the sequenced Neanderthal woman. Her parent’s close relatedness was not exceptional, but rather a normal condition.
12. Neanderthals assimilated with H. sapiens
Maybe Neanderthals did not entirely die out, but by mating with Homo sapiens rather blended into the human populations of Eurasia. The genome of Eurasians contains Neanderthal-genes in small proportions (1-4%). The H. sapiens populations must have been far bigger than that of the Neanderthals or simply far more promiscuous and reproductively successful. Maybe due to hard winters, Neanderthals had developed seasonal mating patterns to make sure that babies were born in warm summer seasons. In all-year warm geographical regions close to the equator, Homo sapiens mated and reproduced all years long. Over several generations, Homo sapiens would demographically outnumber Neanderthal populations and absorb the Neanderthal heritage in the modern man.
In 2008, a small pinky bone and 2 molar teeth were found in the Denosiva cave in the Altai mountains. The DNA extracted from the pinky bone was sequenced and pointed towards a species of the genus Homo that was related to Neanderthals and Homo sapiens and existed around 41,000 years ago, thus, at the same time the last Neanderthal generations lived. Denisovians and Neanderthals had common ancestors around 640,000 years ago and common ancestors with Homo sapiens around 800,000 years ago. Possibly, H. heidelbergensis was a common ancestor.
Interestingly the EPAS1 gene, which enables Tibetians to live in low-oxygen heights, can not be found in the genome of any other H. sapiens peoples and not in the DNA of Neanderthals, but it could be found in the DNA of the Denisovians. With the scarce fossil record (a pinky bone and 2 molar teeth), we can not assume, how the Denisovians look like, if they were taller or smaller than Homo sapiens, how their skull looked like and what inner volume it had. Actually, the Denisovians are the first human species, from which we had detailed genome information before having enough fossils to allow for well-based morphological assumptions. More fossils, that are possibly Denisovian fossils are under investigation, among which a lower jaw bone from Tibet (39).