When viewed up close, the Australopithecus-Homo transition has always been murky.
In a world where more than half the population live in cities, and reality is defined by concrete buildings, roads, electricity cables, other human beings, by what we ourselves have created, it is easy to forget that man is an animal distinct from all other animals. We have subdued the world to such an extent that wild nature is excluded, and it re-enters only through the portals of a cultural system that processes reality. Nonetheless, our otherness requires explanation. One explanation is that we have always been different. Another is that we evolved from the animals that most resemble us, the apes.One fossil that sometimes features in discussion is Sahelanthropus. Niklas and Kutschera ranked it among their top ten transitional fossils, characterising it as a mosaic of chimpanzee and hominid features, and in several ways it epitomises the whole debate, enormous significance read into evidence that is predominantly missing (the fossil is a fragmentary jawless skull), great media fanfare at the time of its discovery, academic disagreement thereafter. A mosaic of features from distinct lineages does not make for an ideal ancestor, and in this case the skull had more features that were not chimp-like than that were, such as pronounced brow ridge, no muzzle, relatively thick tooth enamel and low rounded teeth cusps. Some, accordingly, have suggested that Sahelanthropus was a proto-gorilla. In order to keep the discussion within bounds, we will mostly focus on the later, more relevant fossils: the bipedal australopithecines and early Homo.
Hominids (or “hominins” if orangutans are excluded) are a taxonomic family consisting of humans and great apes, belief in their evolutionary kinship being so ingrained that it is fixed in the definition. Apes are a branch of the order primates, with which man shares a number of features, including:
- finger nails, an opposable thumb and a big toe
- stereoscopic, colour vision
- two mammary glands located on the breast
- usually single offspring
- a large brain compared to body size
The list could be longer, but however long it is, the striking thing is that the features are not unique. Opposable thumbs, for instance, also distinguish the opossums; manatees have fingernails; birds of prey have stereoscopic colour vision; elephants have two pectoral mammary glands and single offspring; and mice have a large brain-to-body-mass ratio. By themselves they tell us nothing about relationships. What makes primates distinct is not the possession of unique features but the possession of a unique association of features. Although also not unique, the main specialisation of the primates is arboreality, the ability to live in trees.
So, is man part of this general picture, or does he possess features that are sufficiently distinct, as a package, for him to be differentiated from the primates? If we restrict our consideration to the apes, the branch which he most resembles, similarities include the lack of a tail, the ability to move the arms above the head, a broad chest, a short lower back, more flexible hips, ankles and thumbs, and a more erect posture. But similarities may or may not be evidence of an evolutionary relationship. Differences are also important, especially if the interval in which the evolution hypothesis requires them to have arisen is very short. The principal differences are:
|1||Brain size small, up to about 400 cc||Brain size larger, average about 1350 cc|
|2||No neck, spine joins skull from the back; extensive muscular connections between head and shoulder; muscles attached to nuchal crest stabilise forward-oriented head||Neck, spine joins skull from below; no nuchal crest; head stabilised during running by nuchal ligament|
|3||C-shaped spine for walking on all fours, sacrum narrow, straight and parallel to spine; typically four lumbar vertebrae||S-shaped spine for upright stance and walking, sacrum broad, curved and tilted; typically five lumbar vertebrae, larger than in apes|
|4||Blades of iliac crest (upper part of hipbone) flat and parallel to each other||Blades turned backward and projecting to increase leverage of spine muscles|
|5||30 facial muscles for expression and recognition||54 facial muscles for more complex social relationships|
|6||Small semi-circular canals in the inner ear||Large semi-circular canals in the inner ear, for balance in the vertical plane|
|7||Arms longer than the legs||Legs longer than the arms|
|8||Chest funnel-shaped||Chest barrel-shaped|
|9||Hands have a weak relatively short thumb, long curved finger bones and long palm||Strong mobile thumb (3 additional muscles) connected to wrist by saddle joint; finger bones straight; apical tufts|
|10||Feet are like hands, with opposable big toes for grasping; apes usually walk on all fours||Feet are arched, and used for walking rather than climbing; big toe not opposable|
|11||Knee joints do not lock upright||Knee joints are bigger and lock upright|
|12||Hip joints do not extend fully upright and pelvis is broad; apes can stand only with legs bent||Hip joints extend upright; large buttock muscles and pelvic attachment areas aid running|
|13||Short Achilles tendon; medial arch of the foot is low||Long Achilles tendon (for running); high medial arch|
|14||Hairy body for heat insulation, no female pubic hair or male top lip; nails grow quickly; fewer sweat glands||Constantly growing hair on top of head; hairy male face, pubic hair, elsewhere hair is fine and sparse; nails grow slowly|
|15||Sclera of the eye (surrounding the iris) is brown||Sclera is white; eyes horizontally more elongated|
|16||Larynx and vocal cords capable of only simple sounds||Larynx and vocal cords capable of complex sounds, including singing|
|17||Ears sensitive to frequencies of 1-8 kilohertz||Ears sensitive to frequencies of 2-4 kilohertz (suitable for hearing speech)|
|18||No hymen in female; males mate from behind||Hymen in female; vulva at 45° angle to permit frontal mating|
|19||Mammary glands purely for milk production; female breasts are small||Female breasts enhanced by body fat for attractiveness/beauty|
|20||Ovulation (fertility) apparent||Ovulation concealed|
|21||Birth of young easy and rapid; broad pelvic canal||Birth of young painful and slow, though may have been easier when crania were smaller|
|23||Male has a penis bone (baculum) for erection; female has a clitoral bone.||Penis boneless, erection achieved by blood; no clitoral bone|
In total, these differences represent a high mountain for Darwinian evolution (natural selection working on chance mutations) to climb, to say nothing about mental and spiritual differences. It is often claimed that in their genetic make-up chimpanzees and humans are very similar. However, if that were so (recent findings indicate otherwise), the similarity in genes would be paradoxical, for anatomically there is a gulf. The supposition that apes and humans as known today belong to the same phylogenetic family does not, on the anatomical facts, seem justified.
Differences that are capable of showing up in the fossil record may, of course, have been smaller in the past and have dwindled backwards in time towards a common root. Or the two groups might not be related at all, whether or not the differences were once smaller. That remains to be seen. As usual, the reader interested in such questions will have to put a little effort into mastering some new terms (mostly species names). However, do that and you will end up equipped to form your own judgement as to whether apes and man are related. Whatever your starting position, be prepared to change your mind, for the story that emerges may be surprising.
Overview of the claimed hominid lineage
Perhaps the best introduction to the fossil record is by way of a diagram such as the one below (Lieberman 2009, adapted), showing the species considered relevant to the story of man’s evolutionary prehistory and their suggested relationships.
Note that humans are not thought to descend from modern-day apes but from the australopithecines (coloured light and dark orange in the diagram). While the differences between extant humans and apes are certainly relevant, we are not retracing the history of both lineages when we go back through the fossil record. We are comparing human beings with apes that are long extinct, possibly as a result of human beings hunting them to extinction. This is a handicap, in addition to the poverty of the fossil record. Worse still, with the solitary exception of one mid-Pleistocene chimpanzee, gorillas and chimpanzees have no fossil record at all across the period covered (hence their absence from the diagram).
A jawless skull. Described as looking like an australopithecine from the front and a chimpanzee from behind. Initial claims that the animal was bipedal, i.e. walked on two legs, have since been disputed (Wolpoff et al 2004), making its hominid status problematic, hominids are bipedal almost by definition. To add to the controversy, the scientific report of the fossil made no mention of its being found out of context, lying on desert sand [photographed here]. Although the age is fairly secure, it does not fit well with assumptions about when hominins and orangutans began to diverge.
This taxon is represented by more than 100 specimens and is much better known. It lived in woodlands, moved along the branches with its palms and was bipedal to some degree. It had very long arms and, like other apes, had an opposable (divergent) big toe, suited to climbing. However, according to the report (Lovejoy et al 2009), its body-plan bore “little or no functional relationship to the highly derived suspension, vertical climbing, knuckle-walking, and facultative bipedality of extant African apes”. To some specialists, its remoteness from the chimpanzee body-plan implies it was close to the common ancestor of what only later became the distinctive chimpanzee and australopithecine forms. To others its dissimilarity indicates it was on another line altogether, and such features as it shared with the australopithecines evolved in parallel. Either way, Ardipithecus is unlikely to have been the australopithecines’ ancestor, despite living at the right time. Indeed, no one knows where the australopithecines came from.
Will the true Australopithecus stand up?
“Facultative bipedality” means an ability to walk on two legs in short bursts, distinct from habitual or obligate bipedality where walking on two legs is the usual or only mode of locomotion. The australopithecines appear to have been, at best, habitual bipeds. The relevant pelvic and foot bones are often either missing or not found with the rest of the skeleton, so the degree of bipedality is difficult to assess, but their overall body plan appears to have been ape-like, not human. The relatively high arm-to-leg-length ratio and forearm-to-humerus length ratio suggest they spent most of their time in the trees, where they moved along branches with an erect posture as their hands obtained additional support from branches above. Habitual hand-assisted bipedality in the trees, a credible scenario for at least some of the australopithecines, should not be confused with habitual free-standing bipedality on the ground, for which the australopithecines show no clear evidence.
“Lucy”, or AL 288-1, the best preserved example of Australo- pithecus afarensis, came from Hadar, a village in the Afar region of Ethiopia just 10 km from Gona (“AL” stands for Afar Locality). The environment of the time fluctuated between woodland and grassland, and Lucy’s anatomy appears to have been that of a bipedal animal. The degree of her bipedality has been the subject of unending debate, with opposing camps doubting not only the interpretation of each other’s data but even their accuracy (Stern 2000). Statements that “Lucy was a primitive hominin, with a brain roughly the size of a chimpanzee’s, but at 3.2 million years old, she already walked upright like we do” may be correct but convey the impression that her small brain and body size were non-human features, which is incorrect. There is nothing distinctively ape-like about her. The preserved roughly 30% of her skeleton still leaves room for a lot of uncertainty, and Lucy may not be representative of A. afarensis at all. The concept of an ape-like species called afarensis has to be supplemented from other bones, some of which may belong to a different species altogether.
A case in point is the semi-circular canals of the inner ear, which are important for balance. Although Lucy is virtually headless, the semi-circular canals of another partial skeleton attributed to afarensis resemble those of extant great apes more than modern humans (Alemseged et al 2006). Her skeleton includes hardly any foot bones, but toe bones (AL 333-115) from relatively nearby show the curvature characteristic of arboreal apes. An arboreal habitat is also indicated by curved finger bones and an upwardly oriented shoulder socket, but again these are not part of the Lucy skeleton, so we do not know that these belong to the same species. Conversely, a recently described fourth metatarsal (AL 333-160) is indistinguishable from the metatarsal of a human foot, and the only reason it is attributed to an australopithecine called afarensis is because “A. afarensis is the only hominin known from Hadar”, a logic that is suspect considering that the region has thrown up quite a few human-like bones, to say nothing of the Lucy skeleton itself. When Lucy is supplemented with the head of an ape from elsewhere in the region (again on the basis that “afarensis is the only hominin known from Hadar”), “A. afarensis” becomes much less human-like.
There is no consensus as to which extinct ape species might have given rise to Homo. The species depicted as ancestral in the diagram is Australopithecus garhi, from the Awash River Valley in Ethiopia. It is dated to c. 2.5 Ma ago. The remains consist of teeth and a partial cranium, enough to infer a cranial capacity of about 450 cc (about average for the genus) but not enough to make any confident link with Homo. What we have suggests non-relationship. It had a sagittal crest at the top of the skull for anchoring large chewing muscles, its upper jaw (unlike that of Sahelanthropus) jutted out prominently, and although the dental arcade was U-shaped, the molars and canines were huge. A few hundred metres distant lay an antelope bone with cuts and percussion marks made by stone tools. The discarded femur of a horse also bore cut marks. Large mammals at this lakeside site were being butchered for meat and their long bones broken to extract marrow. Although the tools themselves were not recovered, stone cores and flakes were found 96 km to the north at Gona, where the raw materials for tools were plentiful. At the lake there were no such materials, presumably because the butchers were conserving their tools for future use. Was the skull of Australopithecus garhi also the remains of a meal, or the remains of one of the tool-making meat-eaters? Clearly the textbooks need to be rewritten if Homo was a predator rather than descendant of the australopithecines.
Africanus, although the first to be dubbed an australopithecine, is very poorly known. The taxon was invented in 1924 to describe the skull of a young human child (the “Taung Child”). Some other material, including a hip joint which shows the functionality of a habitual biped, is also human; other elements attributed to A. africanus are not and might therefore be genuinely be australopithecine. Like afarensis, the species is a composite, a modern-day “Piltdown Man”, except that no hoaxer put his disjointed bones together and the palaeoanthropological community have simply deceived themselves. Some of the bones are no older than the earliest acknowledged human fossils.
Also contemporary with early Homo, the later australopithecines boisei and robustus developed thicker cranial walls, pronounced sagittal crests, huge teeth and huge jaws. In these respects they were on a trajectory at odds with the evolutionary trends shown by man himself. Boisei changed little over the presumed more than 1 million years of its existence and, despite its large teeth, appears to have eaten grass. The recently discovered “Australopithecus sediba” as so diagnosed represents an even greater evolutionary puzzle. Most of its features were like those of early Homo, with which it was contemporary. While it had a small brain, it also had a small body, at a time when human brain and body size was both smaller and more variable. Large brains do not necessarily mean greater intelligence, nor vice versa. Homo floriensis, the diminutive “hobbit” inhabitant of the island of Flores, dating to comparatively recent times, had a brain of only 417 cc, about the same size as sediba. In the light of such finds we may need to rethink what it means to be human.
Early human beings
At the point where Homo fossils appear on the scene (columns coloured blue in the diagram) the fossil record gets even more interesting, and difficult to decipher. There was no smooth transition from Australopithecus to Homo. There was a gap, as shown by the dotted lines, due either to lack of relationship or lack of decisive fossils. The oldest known Homo is H. habilis. Fossils typically consist of a crushed, incomplete cranium, a few teeth or a few limb bones. One of the controversies surrounding H. habilis concerns how much of the assigned material actually does belong to the taxon. If australopithecine limb bones and human skulls have been mixed together, its (to some extent) intermediate character may be spurious. The oldest sufficiently complete skulls to permit an estimation of brain volume (at 510-750 cc) are dated to 1.9 million years ago.
What is clear is that Homo has not remained static. He does not have an ideal form, as visualised in Greek statuary or as the species concept itself implies. At any one time variability within species, including human beings, can be enormous. So can the extent to which morphology within the same lineage changes over time. Species change over time because the environments to which they are adapted change, species must therefore continue to adapt. A shift in climate, for example, may result in a less wooded, grassier landscape and a consequent shift in the kind of food available, in which case the size and shape of the teeth, the jaw and the musculature around the jaw may need to be reconfigured. The purpose of the jaw apparatus is to enable efficient diet-appropriate mastication, not to facilitate differentiation between species. Man has not always been an agriculturalist, or a meat-eater, and may not always have used fire for cooking. A difference in dentition between then and now does not necessarily betoken a difference in species.
Taxonomists (being themselves subject to classification) tend to be either “lumpers” or “splitters”, according to how ready they are to interpret differences as evidence of separate species or as minor variations within the same species. Theoretically, a species is the generalised identity of all individuals that can interbreed, but that is not a possibility one can determine from fossils. Whether, say, Homo erectus and Homo neanderthalensis could interbreed is a matter of judgement, and opinions differ. One factor in forming a judgement is whether one accepts that man evolved from apes at all. A succession of species, carrying on the baton of evolution from one boundary to the next, lends more credibility to the idea than a continually evolving species whose history does not consist in the crossing of successive boundaries. Also, a new species earns its discoverer greater prestige than the variant of an existing one. These factors affect perceptions about the course of australopithecine evolution as well as human. Dissatisfied with the chaos resulting from the lack of an agreed methodology for identifying species, one researcher went so far as to call for the assigning of new names to be suspended (Quintyn 2009).
Early human bipedality
Bipedality is often regarded as the key to becoming human, but as with so many other traits, bipedality is not unique to humans or hominids. Some of the earliest reptiles were bipeds. So were some dinosaurs, including the earliest. We know of at least one extinct non-hominid ape that was bipedal (Oreopithecus). Among facultative bipeds today are several kinds of lizard, bears, kangaroos, several kinds of rodent (including kangaroo rats and mice), various kinds of flightless bird (if not all birds), cockroaches and some insects. The zebra-tailed lizard can run at up to 5.3 m/s, equivalent to 50 body-lengths per second. In a number of these instances bipedality is an evolved trait, i.e. ancestor species did not have the same ability. Thus it is not a uniquely human trait. While all humans are bipeds, not all bipeds are humans.
On the other hand, no animal walks or runs in quite the same manner as humans. Substantially larger articulating surface areas relative to body mass in the joints of the lower body, including the femoral head and knee, the sacroiliac joint and the lumbar vertebrae, lower the stresses that impact forces generate at heel strike during walking, and help to dissipate the much higher impact loads generated during running (Bramble & Lieberman 2004). “We keep the trunk erect; in walking, our knees are almost straight at mid-stance; the forces our feet exert on the ground are very markedly two-peaked when we walk fast; and in walking and usually in running we strike the ground initially with the heel alone.” (Alexander 2004)
Apart from man, no primates have ever been obligate bipeds, none appear to have been even habitually bipedal except, possibly, in the trees, and none have ever been capable of long-distance running. The living great apes are habitual quadrupeds. Whether one then interprets the optimal design of the human body for walking and running as showing that man has always been distinct from apes, or that he represents the final stage in a trend of increasing bipedality, depends on philosophical predisposition. The fossil evidence shows no such trend. The australopithecines show an increased degree of bipedality, but they came and went; the living apes are not bipedal.
Homo‘s foot is unique and an engineering marvel, with 26 bones, 30 joints, 19 muscles, 115 ligaments and 250,000 sweat glands, but ligaments and sweat glands do not leave fossils. As regards the skeletal elements, one of the key ape-to-man transformations relates to the big toe (hallux), which in apes is a divergent digit designed for grasping, in man a convergent digit designed for weight-bearing, balance and propulsion. Evidence for such a transformation is lacking. “There is no evidence of any ape living or extinct that gave up hallucial divergence.” (McHenry & Jones 2006) Even apes that normally live on the ground, such as gorillas, have divergent big toes.
The oldest bone fossil (distinct from tools and tracks) unequivocally belonging to Homo is a temporal bone dated to 2.4 million years ago in the received chronology. A relatively well-preserved foot from Olduvai, labelled OH 8, dates to around 1.8 million years ago. Although not preserved, the big toe seems to have been convergent, and as in humans, the foot was longitudinally arched (Berillon 2003). Arching improves the efficiency of locomotion in two ways: by acting as a spring during running and by providing rigidity to the foot as it toes off.
The oldest members of Homo to preserve both a complete hind limb and partial foot are those from Dmanisi, Georgia. Dated to 1.77 Ma and among the earliest humans known outside Africa, the Dmanisi individuals were short-statured (1.45 to 1.66 m) and had small brains (600 to 775 cc). Relative to body mass, the hind limb was longer than that of African apes and A. afarensis and within the lower range of values for modern humans (Pontzer et al 2010). The foot was also functionally similar to that of modern humans, with the characteristic ankle-joint, mid-foot arch and convergent toe. Cultural indications, stone tools and evidence of hunting and/or scavenging, were consistent with this evidence of walking and running ability.
The oldest virtually complete skeleton, KNM-WT 15000, from Nariokotome, Kenya, dates to 1.53 Ma. In morphology it is obviously and entirely human, and belongs to an adolescent boy about 5′ 4” (163 cm) tall (Graves et al 2010, who revised the age and height substantially downwards). As with the Dmanisi individuals, he was capable of travelling long distances, and in all probability lived by foraging and hunting.
The interpretative framework
The evidence reviewed so far indicates (1) that there has always been a wide anatomical gap between apes and humans, notwithstanding that apes and humans have each been continually evolving, and (2) that the discontinuity corresponds with the appearance of Homo fossils around “2 million years ago”. The distinction between Homo and Australopithecus, in other words, coincides with a difference significantly greater than that between the perceived species within those categories. In the framework developed on the Earth History website, the true date would be much lower. Dating systems based on radioactive decay exaggerate true time, but to a progressively lesser extent as time passes. Consequently the final 2 million years as measured by isotope dating would represent much more than 2/4567ths of Earth’s total history, around one third.
The lateness of man’s appearance was proportional to the time environments took, following the end-Hadean cataclysm, to stabilise towards the conditions that are normal today, conditions that permitted long-distance exploration, hunting, settlement, and eventually agriculture. The extraordinary acceleration in the pace of change over the last five thousand years, recording the rise of civilisation from ziggurats to skyscrapers and the growth in population from a few million to almost seven billion, is what followed when man responded to the new opportunities. The Earth had returned to something close to the stability that existed before the cataclysm. In comparison with the rest of history, the slow pace of geological change and the rapid pace of cultural change were far from typical.
Human fossils are therefore extremely rare when they first appear, man’s population being then neither numerous nor widespread. The entrance of the species that arose, according to evolution theory, as a result of outcompeting its australopithecine relatives was unspectacular. (Extant great apes have virtually no fossil record at all.) In the received chronology five hundred thousand years separate the earliest human skull and the earliest complete skeleton of a human, longer, probably, than the true time-span of the planet’s entire history. Five hundred thousand years also separate the oldest known stone tools from the first human skull. Hominids of some description, we have seen, were making tools at Gona and butchering animals with them as early as 2.5 Ma ago, and the very oldest known tools, from the same region, go back to 2.6 Ma. The identity of the tool-maker has to be determined on circumstantial evidence, involving an assessment of which species might have been capable of the technology. Palaeoanthropologists are reluctant to suppose that it could have been Homo, despite the “sophisticated understanding of stone fracture mechanics” revealed by the tools, the clear association with Homo later in the record and the inability of any living ape species to replicate them. The tools were used for preparing his dinner, which as at 1.95 Ma ago included turtle, crocodile, fish, bovids, hippopotamus, rhinoceros (Braun et al 2010) and probably also australopithecines.
|Received date||Evidence of Homo|
|3.66 Ma||Oldest footprints|
|2.58 Ma||Oldest stone tools|
|2.42 Ma||Oldest bone fossils|
|1.53 Ma||Oldest human skeleton|
In addition to bones and tools, there is also the evidence of footprints. The oldest known human-like footprints are at Laetoli, imprinted 3.66 Ma ago on a surface of wet volcanic ash from the Ngorongoro volcano (East African Rift Valley). The pattern is clearly bipedal, with a stride length within the range of modern humans (though small), and made by feet that were arched and had big toes parallel to the other toes. These traces precede the oldest human body fossils by a further 1 million years.
Because of their age the prints have been much debated. Were they really as human-like as they appeared? Could perhaps an australopithecine have made the prints, the contemporaneous “Lucy”, for example? While it was difficult to imagine feet with curved phalanges of afarensis fitting neatly into them, formation in the course of a “bent knee, bent hip” gait could not be, or was not, discounted. It now can. Experiments have shown that the latter type of gait would have resulted in toe impressions significantly deeper than heel impressions, whereas at Laetoli the impressions are about equally deep. As such they are characteristic of fully erect, human-type walking (Raichlen et al 2010), the kind of walking that the fourth metatarsal labelled AL 333-160 was capable of.
Much like the tetrapod footprints that predate the time when tetrapods supposedly evolved from fish, these footprints effectively invalidate the idea that man evolved from australo- pithecines 2.5 to 2.0 million years ago. Upright, obligately bipedal Homo was already in existence.
Kadanuumuu (“Big Man”) – the footprint-maker found
That was the state of affairs as of June 2010: human trace fossils preceded the oldest body fossils by more than 1 million years. But if the footprints were made by human beings, the implication had to be that contemporary recognisably human bones would sooner or later turn up. Anthropologists committed to the idea that Homo could not have been in existence 3.6 millions years ago would then be in a quandary. They could hardly suppress such a discovery. But nor would it be an option to admit that Homo was contemporary with the only animal that could be his ancestor. In the event the discovery of a partial skeleton labelled KSD-VP-1/1, not far from Gona inspired another solution: announce the fossil as that of an australopithecine and then characterise the Homo-like features as evolutionarily advanced. If the long-touted Lucy had to be repudiated, so be it:
The new A. afarensis specimen stood between 5 and 5 1/2 feet tall, towering over Lucy’s 3-foot height. Other fossil fragments suggested that Lucy was an unreliable measuring stick for A. afarensis, but the new fossil is the most conclusive evidence yet. Dubbed “Kadanuumuu” or Big Man, it is described June 21 in the Proceedings of the National Academy of Sciences.
Big Man’s limbs also appear well-suited for running, in contrast to the shortened gait implied by Lucy’s skeleton. The proportions compare to those found two million years later in Homo erectus, and would not be out of place in a modern human, said study co-author Owen Lovejoy, a Kent State University paleoanthropologist.
“The difference between Australopithecus and humans is much less than everyone expected” said Lovejoy. “Upright walking and running were pretty advanced at 3.6 million years ago, and they didn’t change much over the next two million years. Most of the changes in that period of time took place elsewhere.”
The report itself does almost nothing to justify the preferred attribution. It compares the fossil chiefly with two known species, A. afarensis as represented by Lucy (who, although diminutive, was herself a human being) and Homo sapiens. As often as not, the comparisons show that Kadanuumuu was more similar to Homo than to Lucy. Over 5 feet tall, erect, capable of running and little different from the Homo fossils known from two million years later, Kadanuumuu appears to have been, as his nickname signifies, just a big man.
Two months later, in August 2010, came news that animal bones with “unambiguous stone-tool cut marks for flesh removal and percussion marks for marrow access” had been found a few miles from Hadar and Gona. Yet more evidence of Homo in the region? Not so far as the discoverers were concerned. As they wrote in Nature, “The only hominin species present in the Lower Awash Valley at 3.39 Myr ago to which we can associate this tool use is A. afarensis.”