Out of Africa

The likelihood that archaic hominins left Africa on more than one occasion during the Lower and Middle Pleistocene has already been raised several times. But so far there is really only one situation in the combined archaeological and fossil records that suggests this. In eastern Africa, the distinctive bifacial hand axe industry that archaeologists term the Acheulian (Figure 3.4) had developed in nascent form from its Oldowan predecessor by 1.8 million years ago. There is a general assumption by archaeologists that the Acheulian represented something technologically and conceptually different from the Oldowan, even though some developed Oldowan tools were bifacially flaked. Outside Africa, Acheulian technology occurs at Ubeidiya in the Jordan valley in Israel by

Possibly 1.6 million years ago and perhaps earlier than one million years ago in southern India.26 But its spread was fairly limited until about 800,000 years ago, after which bifacial hand axes are found in many regions of Africa and Eurasia, to as far north as Great Britain and eastwards to the Black Sea, Kazakhstan, the Altai Mountains, and Mongolia.27

These widespread Acheulian industries in the western and central Old World are believed to be associated with Homo heidelbergensis, a fairly brainy hominin (averaging about 1250 ccs in cranial capacity) represented by fossils from a number of African and Eurasian locations that include Broken Hill (Kabwe) in Zambia, Bodo in Ethiopia (dated to 600,000 years ago), Mauer (near Heidelberg) in Germany, Ceprano in Italy, Petralona in Greece, and Hathnora in the Narmada Valley in India. Because of the large number of fossil and hand axe discoveries, there is considerable support for a migration, around 800,000 years ago, of H. heidelbergensis from Africa into Western Eurasia, with part of the species remaining in tropical Africa and undergoing separate evolution there in the direction of modern H. sapiens (Figure 3.1).

H. heidelbergensis was thus the potential common ancestor for both evolving modern humans in Africa, and Neanderthals and allied species such as the Denisova hominin (see following text) in Eurasia. The genetic split between these two groups has been dated recently by nuclear DNA molecular clock calculations to something under

840,000 years ago, alas a little uncertain, but still within the range of an Out of Africa 2.28 In Europe, incoming heidelbergensis presumably replaced or mixed with the earlier hominins represented in Sima del Elefante and Gran Dolina at Atapuerca in northern Spain, and then evolved into the Neanderthals of the Upper Pleistocene.

Some of the contemporary Paleolithic assemblages of China, Korea and Java also have bifacial hand axes, together with the more ubiquitous unifacial pebble and flake tools, for example, the finds from Bose in Guangxi, southern China.29 Nevertheless, the hand axes do not seem to be sufficiently prominent for a separate layer of human migration to be invoked in these regions. However, the evidence for a possible arrival in Java of a new hominin species at about 800,000 years ago could be relevant here. The Javan fossils cannot be assimilated into H. heidelbergensis and are firmly erectus in taxonomic terms, but this possible secondary arrival could have been a repercussion of other population movements elsewhere on the Asian mainland. It is therefore possible that heidelbergensis, in the strict biological sense, did not migrate beyond India, but that cultural and perhaps even some biological repercussions extended as far as China and Indonesia.

H. heidelbergensis was also the first species to penetrate really cold latitudes, up to 53°N in southern England, Germany, and possibly the Altai Mountains of Russia. As discussed already questions arise concerning hominin survival at such latitudes during glaciations, or through extremely cold winters in interglacial periods, remembering that actual glaciers and ice sheets were features only of northern Europe and North America. The drier parts of Siberia east of the Taymyr Peninsula would have been mostly in the grip of deep permafrost rather than ice sheets. Perhaps people either retreated south during glaciation periods, or simply died out. Clothing and fire would naturally have been useful during such northerly excursions. As discussed in Chapter 5,

It is clear from ethnographic accounts that Australians could withstand very cold winter temperatures in regions such as Tasmania with only marsupial fur cloaks wrapped around their upper bodies, showing a fortitude that greatly impressed early European visitors (Mulvaney 2008). Perhaps earlier hominins were equally hardy

As for penetration of such regions when conditions were good, Leroy et al. (2011) point out that movement into high Eurasian latitudes would have been easiest during the early phases of glacial retreat, rather than during interglacial high points. This is because the spread of dense temperate forest and the drowning of continental shelves by rising seas lagged several millennia behind the commencement of postglacial temperature rise, as explained by Broecker (2000). In other words, warmer temperatures developed whilst land bridges and open rather than densely forested landscapes still remained, for a few millennia at least. Faunal and pollen data from many archaeological sites indicate that early hominins in Eurasia, as in Africa, preferred open grassland or forest steppe conditions rather than dense forest. Some southerly heidelbergensis populations, such as those from Atapuerca in Spain, were able to occupy open woodlands virtually continuously, through hundreds of millennia, but such benign conditions would have diminished quite rapidly north of southern France.30 Indeed, we know that a major expansion from southern refuges into northern Europe occurred as conditions improved after the last glaciation, between 19,500 and 14,000 years ago (see Chapter 5), so it is likely that hominins congregated for warmth in similar southern latitudes during earlier glaciations as well.

There are also suggestions of very prolonged periods of aridity in southwestern Asia that would have hampered both mammal and hominin migration from Africa. Van der Made (2011), for instance, suggests that such conditions existed between 1.8 and 0.9 million years ago, which agrees quite well with the suggested commencement date for heidelbergensis migration from Africa into Eurasia around 800,000 years ago. However, a contrasting suggestion is that early hominin migrations into Eurasia were not attached directly to those of other mammal species at all (O'Regan et al. 2011). If this is true, then hominins might have acted alone in their migratory quests, perhaps assisted by increasing investments in cultural paraphernalia. This raises a fundamental question; were early hominins rigidly bound by climatic parameters in their migratory movements, or could they ignore them as brain capacity evolved, to an increasing degree through time? We are still far from knowing the answer for hominin species prior to the appearance of H. sapiens, but I would expect the latter answer to be at least partly correct.