Written by Graham | Created: Saturday 6th July 2019 @ 0005hrs | Revised: Thursday 1st October 2020 @ 1223hrs
Some time around 7.5 mya, the evolutionary lineages which would lead to humans and the chimpanzees diverged. 500,000 years later, a new species of Hominin was ekeing out a living in what is today the Djurab Desert in the African country of Chad, and perhaps spending some periods of time walking on two legs. Some remains of a member of this species, given the name Toumaï, were discovered in the early part of the third millennium, and were assigned the binomial name Sahelanthropus tchadensis. Slightly earlier, the first of a series of fossils belonging to the species Orrorin turgensis were uncovered in Kenya. Orrorin shares a number of features with us which differ from later human ancestors, particularly in terms of its dentition (the make-up of its teeth), and Orrorin may also have spent time walking upright.
One possible reason for this novel means of locomotion is an unusually high numbers of wildfires between 7 and 8 mya - potentially caused by a supernova! - which transformed the swathes of forest which covered parts of Africa into something resembling the savannas and grasslands we see today. Another such event, between 2 and 3 mya, likely sealed the deal. Walking upright would have been an advantage in that it allowed these small apes to peer over the heads of the grasses to get advanced warning about predators lurking in the area, such as the sabre-toothed cat Dinofelis, as well as staking out potential meals of their own from afar.
By about 5.5 mya, a new genus, Ardipithecus developed, and is represented by two known species: the Miocene A. kadabba and Pliocene A. ramidus.
By about 4.2 mya, the genus Australopithecus had emerged in eastern and southern Africa, being represented by A. anamensis. A. anamensis soon transitioned into A. afarensis, which lived for a period of about a million years from 3.9 mya. Australopithecus is more suited to bipedal walking than Ardipithecus and its predecessors, which appear to have spent more time in the trees and less on the ground. Two related species, A. bahrelghazali and A. deyiremeda, appeared about 3.5 mya, with A. africanus - the first member of the genus to be discovered - evolving shortly thereafter. Also present at this time was a new genus, represented by Kenyanthropus platyops, and it is this species which may well have initiated tool shaping among the hominins: the earliest-known lithic industry is the Lomekwian, which dates from about 3.3 mya, and was uncovered at the Lomekwi 3 site in Kenya, in close proximity (both physically and temporally) to strata bearing Kenyanthropus fossils. The Lomekwian industry precedes the Oldowan or Mode I - from which the later stone tool industries derive - by some 700,000 years.
The Oldowan industry may well have been developed by a later Australopithecus species, A. garhi, which emerged around the same time, as the Pliocene epoch drew to a close. A. garhi was contemporary with the last 500,000 years or so of the lifespan of A. africanus, with the last species assigned to the genus Australopithecus, the more advanced and Homo-like A. sediba appearing around 2 mya.
Another genus, Paranthropus, appeared at about the same time as the Oldowan technology, and is represented in the fossil record by three known species. Paranthropus is characterised by a more robust skull shape than that of the Austalopithecines, bearing a sagittal crest across the top of its head similar to that of a gorilla, and pronounced attachments for strong muscles capable of chewing tough vegetation. Paranthropus also has a cranial capacity similar to that of the earlier Australopithecines, which enables us to conclude that Paranthropus is a more specialised hominin, diverging markedly from the lineage leading to us.
The earliest member of the genus is P. aethiopicus, which dates between 2.7 and 2.5 mya, and likely gave rise to P. boisei, which appears shortly after the latest known member of P. aethiopicus. P. boisei survived until shortly before 1 mya, and, for much of its lifespan, it was contemporary with the third species, P. robustus. P. robustus is particularly interesting in that it shared more features with A. africanus than its fellow Paranthropus species. These affinities might suggest that Paranthropus was paraphyletic.
The earliest-known species assigned to our own genus, Homo, was also living during this time period. H. habilis first emerged early in the Pleistocene, about 2.3 mya, and probably died out about 1.5 mya. The transitional nature of this species - seemingly located somewhere between Australopithecus and H. erectus - has led to continuing debate among paleoanthropologists about the validity of its membership of Homo. H. habilis did, however, have a slight increase in cranial capacity over the Australopithecines, up to about half of that of modern humans, with the contemporary A. sediba only packing a third of the amount of grey matter we boast.
Subsequently, two more species of Homo appear: H. ergaster and H. erectus. Of these, the former is a chronospecies which dwelt in Africa between 1.9 and 1.4 mya. H. ergaster can be seen as an African variety of H. erectus, the first human species to leave Africa.
H. erectus, of which there are any number of proposed subspecies, is associated with the transition from the Oldowan to the Acheulean (Mode II) stone tool industry, and its dispersal into western Europe and southern Asia. The earliest known representatives outside of Africa have been found in the Dmanisi cave in Georgia, and date from about 1.8 mya. During the course of the next 500,000 years, the species made its way into modern China, travelling as far as Java in Indonesia by about 1.4 mya. The latter subspecies, H. e. palaeojavanicus, is sometimes known as Meganthropus on account of the large jaw fragment discovered in 1941 by Gustav von Koenigswald, which has led to various unfounded theories about this species supposedly being of gigantic proportions.
H. erectus is attested throughout China and Indonesia for well over a million years, yielding iconic fossils such as Java Man (c.1-0.7 mya) and Peking Man (c.0.7 mya), surviving until perhaps as recently as 143,000 ya, in the form of Ngandong (Solo Man), who dwelt along the Solo River on Java. Meanwhile, in China, Nanjing Man survived until perhaps about 250,000 ya, with his contemporary Yuanmou Man pehaps dating from about 500,000 ya. H. erectus also persisted surprisingly late in Europe, depending on the interpretation of human remains from Bilzingsleben, Germany (which date from some 370,000 ya and show possible signs of ritual activity around disposal of the dead). Tautavel Man, discovered in the Caune de l'Arago near Tautavel, France, dates from about 450,000 ya.
The most recent in date - and remarkable - finds related to this early human dispersal are probably the small hominid species found on islands in the western Pacific Ocean. Thus far, two new species of Homo have been described. H. floresiensis, otherwise known by its Tolkien-derived nickname "hobbit," lived on the Indonesian island of Flores up until about 50,000 ya, while H. luzonensis, a taxon described as recently as 2019, inhabited Luzon in the Philippines at around the same time. These species represent descendants of H. erectus displaying "island dwarfism" - and, as such, it is worth noting that, close to the cave of Liang Bua, in which the remains of H. florensis were discovered, live a group of people called the Rampasasa, inhabitants of Waemulu village, who also display traits island dwarfism. There is, however, no genetic connection between the Rampasasa and the hobbit: this is convergent evolution in action.
These small hominins were not the latest enigmatic humans though: about 14,500 to 11,500 years ago, the Maludong ("Red Deer") and Longlin Caves in southern China were inhabited my a mysterious, archaic-looking group with notably large cheekbones. Known as the Red Deer Cave people, this group have been variously explained as archaic humans, robust early modern humans or a stable Denisovan-H. sapiens hybrid population.
Another group of fossils dating from relatively recently (probably about 250,000 ya) indicates that early members of H. sapiens dwelt alongside other hominins with very different morphological traits in Africa. This new species, H. naledi, is found in the Rising Star Cave in Gauteng province, South Africa. H. nadeli bore a number of traits shared with the much earlier H. ergaster and even Australopithecus, in combination with other more derived features. The brain of H. naledi was small, not much more than half that of a typical H. erectus, and the average male member of the species stood about 5 feet in height, slightly smaller than other contemporary members of Homo. Nonetheless, H. naledi's brain was structurally similar to modern human brains, and the species may well have used the cave system as a site for funerary ritual.
Evidence for an archaic human presence has been uncovered in Spain, France and England dating to around 1 mya. These people are members of a proposed species, H. antecessor, though scientists generally ascribe them to H. erectus (as a European variety), or regard them as an earlier form of a species which is likely the immediate forebear of our own: H. heidelbergensis. H. heidelbergensis is known from African and European contexts and, in its developed form, is regarded as having lived between about 750,000 and 250,000 ya. H. heidelbergensis evolved from H. erectus, and the European branch of the species gave rise to the famous Neanderthals (H. neanderthalensis).
Meanwhile, in Africa - where Lee Berger claimed to have uncovered remains of a number of H. heidelbergensis over 7 feet in height (while these assertions have not as yet been published in a peer-reviewed journal that I know of, Berger remains one of the paramount palaeoanthropologists of the early 21st century and, as such, cannot be quite so easily dismissed as many other people claiming to have discovered giants of some description) - the picture is muddied somewhat by the presence of another proposed species, H. rhodesiensis, which may instead by an African form of H. heidelbergensis. Unfortunately, there is at present something of a dearth of African fossils dating from 400,000 to 260,000 ya, so the precise picture of the emergence of H. sapiens from these earlier forms is, as yet, unclear. It must, however, be stated that distinctions between species are rather arbitrary: there was no single point at which, for example, two members of H. erectus became the proud parents of the first H. heidelbergensis. Additionally, the earliest member of H. sapiens identified to date, discovered at Jebel Irhoud in Morocco, dates from 300,000 ya, which suggests a much earlier radiation of H. sapiens than was previously assumed. Furthermore, the Gawis cranium, which could well be even earlier, is regarded as transitional between H. erectus and H. sapiens. Add to this mix the remains of Herto Man, found in Ethiopia and dating to about 160,000 ya, which has been ascribed as a subspecies of our own, H. s. idaltu.
Already by this period, H. sapiens had begun to migrate out of Africa. By 215,000 ya, this early group of explorers - who have seemingly left no trace in our genetic makeup - had made it as far as Greece, where their remains were discovered in 1978. Dali Man, who was also possibly a member of our species, died in China at roughly the same time - and could be taken as indicative of the multiregional hypothesis favoured by some scientists, particularly in China, which posits that modern humans, migrating out of Africa, met and interbred with other Homo species in Europe and Asia.
Europe and western Asia was, by this stage, largely the domain of the Neanderthals. This species boasted the highest cranial capacity of any Homo species (albeit evidence of earlier puberty among Neanderthals than H. sapiens likely means less time to develop quality to go with the quantity), and lived in the inhospitable northern climes of the last Ice Ages, to which they were well-adapted, hunting large game and living off a diet which was almost exclusively made of meat. The Neanderthals were, however, not the grunting cavemen imagined of old: instead, they were artists - the earliest European cave paintings, from about 65,000 ya, were almost certainly the work of the Neanderthals. They likely went extinct around 43,000 ya, mainly through interbreeding with modern humans, bequeathing up to 4% of the DNA of modern non-African humans. Both modern humans and the Neanderthals also interbred with another, highly enigmatic, species known as the Denisovans. This group are represented in the Altai mountains by fragmentary remains, though one specimen, named Denny, is the fossil of a young woman who lived around 90,000 ya and who seems to have been a Neanderthal-Denisovan hybrid. The Denisovans also left a genetic legacy among the Melanesians and indigenous Australians.