Did our remote ancestors behave like us? When it comes to migration we cannot be sure. We know they moved, from Africa to Asia and eventually to Java, but we do not know if the moves were intentional, if they traveled in large or small groups, or if they could swim across large expanses of water. Most likely there would have been range expansions similar to those of other mammal species, dependent on environmental circumstances and probably without conscious intent. The precise details of any given range expansion will be forever lost to us, as they surely are for other ancestral species deep in time. But we can plot some of the approximate time and space coordinates of hominin expansions from the fossil record, and more controversially from genetic molecular clocks. We can also relate them to enabling environmental factors such as the existence of enticing warm climates, familiar food resources, fairly open country (neither intense desert nor dense rainforest), and the availability of land bridges between land masses that were at other times separated by sea.
Did early Homo at two million years ago already have the gendered pair bonding, cooperative sharing, and base-camp territorial systems that characterized ethnographic human hunter-gatherer populations?4 This could be considered an insoluble question, perhaps an irrelevant one for migration studies. But an answer could help in the modeling of migration scenarios, if only because a species organized into large cooperating groups of both sexes, with permeable rather than rigid territorial group boundaries, and perhaps communicating with rudimentary spoken language, would have had a far better chance of successfully colonizing a new and unknown landscape than one without such advantages. They would have had an even better chance if, as suggested by Richard Wrangham (2009), they already knew the use of fire for cooking food by as early as two million years ago. Cooked food allows easier and more rapid digestion than raw food, thus making energy available to be utilized in brain development. Cooking is also an activity that can strengthen the bonds within a family unit, leading to increased male-female cooperation. Whether cooking really was known to hominins two million years ago remains debated, but chimpanzees and bonobos do not use fire and are strongly territorial, which may be partly why they have not had a very successful history of species radiation beyond the equatorial rainforests of Africa.
Getting down to more visible characteristics, the earliest members of the genus Homo in Africa were habitually bipedal, as demonstrated by the almost complete skeleton of the 1.6 million year old 'Turkana Boy' (H. ergaster or H. erectus) from Kenya. Bipedalism is important because it allows us to stride, run, and travel over very large distances, and doubtless allowed our ancestors to migrate much further than would the knuckle-walking posture of a chimpanzee or gorilla. This ability applied equally to both sexes, added to which the sexual dimorphism in body size that characterizes most other higher primates was under gradual reduction at this time, making males and females more equal in size. Overall body sizes for both sexes were also increasing, but brain sizes were still small two million years ago, varying between 500 and 900 ccs, depending on the species concerned. In contrast, Neanderthal and modern human brains of the past 50,000 years averaged over 1200 ccs in brain size.
As far as we know from extant finds, early hominins favored fairly dry tropical and temperate woodlands and parklands south of the fluctuating southern edge of the Sahara Desert, generally quite open, of varying tree and shrub density In fact, given the presence of their fossilized (mineralized) bones in several caves in South Africa, as well as in East Africa, it is likely that early Homo populations occupied nearly the whole continent by two million years ago, except possibly for the most arid Sahara and Kalahari regions. This means that temperature-wise they would have been adapted to life in both tropical and temperate climates, from the Equator to almost 40° of latitude north and south. According to Ruxton and Wilkinson (2011), the loss of thick body hair in our own direct H. sapiens ancestry reflects selection to allow sweating in hot and open tropical environments, but there is no guarantee that all early hominins were hairless. Thick body hair might have been extremely useful to hominins living through a chilly winter in South Africa or Algeria.
In terms of the archaeological record, the earliest African Homo populations struck pebbles and stone nodules with stone hammers to make simple tools, utilizing both cores and flakes. Stone tool making has become one of the essential elements in the definition of Homo, given that no other hominins, apart perhaps from the latest Australopithecines, can yet be proven to have made them. Currently, sites with definite stone tools in Africa go back about 2.6 million years (Hovers and Braun 2009) and strongly suggest a partly meat-eating diet, even if archaeologists cannot easily decide whether the game was hunted by the hominins themselves or scavenged from abandoned carnivore kills. What is more, some of the stone raw materials were carried several kilometers across the landscape. Apes can be taught how to make stone tools by human mentors, and indeed sometimes use them as hammers or anvils in the wild. Some chimpanzees in West Africa leave discarded modified stones around their living places (Mercader et al. 2007), but chimps in the wild do not flake stone tools with focused intent.
How do we know the genus Homo evolved in Africa, and not elsewhere? Human evolution occurs constantly, and humans have certainly evolved as regional populations in Eurasia as well as in Africa. Some populations even moved back into North Africa from Asia during the Holocene, particularly via the Levant and Arabia (Chapter 7). Some have suggested that fossil species of Homo, especially H. erectus, might have evolved in Asia and done the same in the remoter Pleistocene past.5 Once Homo populations were widespread in ancestral form across the Old World, then formation of a new species could have happened, in theory, anywhere within the range, allowing sufficient time and isolation (Stewart and Stringer 2012).
However, in terms of human evolution as a whole, from Miocene and Pliocene primate forebears to early Homo, Africa was undoubtedly our ultimate source. Our closest genetic relatives, chimps and gorillas, have never been found in fossil form elsewhere. All pre-Homo hominin fossils have been found in Africa, as well as the oldest dated stone tools. What is more, as far as modern humans are concerned, the greatest degree of genetic diversity in humans occurs in sub-Saharan Africa. All of the haploid DNA lineages of living people (H. sapiens) across the world first appeared there in their foundation forms, although genetics at present cannot demonstrate this for extinct species of hominin.
Where in Africa did the genus Homo originally speciate? Two regions have produced the bulk of the relevant hominin fossils: the Great Rift Valley of East Africa, and a series of ancient limestone caves in South Africa. In both cases, the landscapes assist paleontologists greatly, since alluvial/lacustrine and cave sediments trap and bury bones which can eventually fossilize, later to be exposed to view by uplift, erosion, or speleological good luck. Many of the geological deposits in the Rift Valley are also derived from volcanoes that feed on the crustal instability, and tuffs and lavas are very useful for radiometric and other forms of absolute dating. Hence, we know a lot about hominin evolution from these two regions.
However, in terms of the totality of Africa, these landscapes are rather localized. The Great Rift Valley is 6000 km long and runs beyond East Africa, via the Red Sea, into the Jordan Valley in the Levant. But much vaster and more stable areas of western and northern Africa do not reveal fossils so easily Australopithecines dating from 3.5 million years ago have been found as far west as northern Chad in the Sahara, but they lived during a moist Pliocene climatic period long before the evolution of Homo, when the Sahara was apparently more habitable than now. So, was the source of the genus Homo actually in the woodlands and parklands of eastern and southern Africa, where so many fossils have been found? Or could it have been elsewhere?
Because of the hominin adaptation, via bipedalism, for extended bouts of walking and running (e. g., after ground-dwelling prey, or away from ground-dwelling predators), An origin in the eastern and generally drier side of sub-Saharan Africa does seem most likely Hominins are not renowned for their tree-climbing capabilities, and many recent hunters and gatherers have found wet tropical rainforest to be rather difficult for food collection and hunting. In 1994, Yves Coppens proposed an “East Side Story” for the origin of humankind, in which humans became separated from the ancestors of chimps and gorillas as the Rift Valley formed and divided sub-Saharan Africa into a wetter west and a drier east. King and Bailey (2006) have put the spotlight on the Rift Valley itself, pointing out that hominins would have been hard-pressed to avoid predators in completely open flat country whereas the Rift would have offered excellent opportunities for early humans to have foraged, hunted, and protected themselves in relatively rough terrain. They point to varied geomorphological features that exist owing to the tectonic instability giving varied and abundant plants and animals, ample water in the form of lakes and rivers, security (cliffs, trees, rough places in general), and perhaps even opportunities for running down animal prey They also note how the Rift Valley would have led people onwards into Asia when the Saharan and Arabian deserts allowed such movement to occur.
In the last few years, a number of scholars have also suggested a southern rather than eastern African origin for Homo (e. g., Pickering et al. 2011). If true, this would be rather interesting in terms of climatic adaptation, since the caves near Johannesburg that have produced so many fossils from the period between 3.5 and two million years ago lie at a latitude of about 30°S. As noted earlier, this would probably have meant cold winters and occasional frosts, especially since these caves are quite far inland. Given that the oldest hominins in Eurasia have also been found far from the Equator, at 41°N in Georgia, it is becoming apparent that archaic hominins as a whole, regardless of specific H. sapiens ancestry were not entirely tropical creatures, but able to survive in much cooler temperate climates as well.
Yet, even here there may be a catch. Christine Hertler and colleagues (2013) suggest that early Australopithecines spread from tropical East Africa to temperate South Africa during a warm climatic phase about 3.5 million years ago. Then they spread back again, as the species Australopithecus africanus, during colder climatic conditions between three and two million years ago, eventually to give rise in East Africa to an early Homo species (H. habilis?) before two million years ago. This suggests an interesting level of climate-related migratory behavior for such an early time period, with Homo ancestors dodging the cold through forward and backward migration. But such scenarios can be little more than working hypotheses at present.
World History
