Saturday, 20 June 2009

Human Evolution on Trial - Out of Africa - by Terry Toohill

Human Evolution on Trial - Out of Africa

Way back (“Time”) the jury saw that the nearer we get to today, the more evidence we find. And all this evidence supports the wave theory of Human Evolution. We can even use the theory to understand evidence capable of several different interpretations. The defence is now ready to use this wave theory of genetic, cultural and technological evolution to help the jury understand our ancient history. The analysis places the evolution of much modern human culture to around the region modern humans first reached when they emerged from Africa: the Middle East. Many people will be able to draw comfort from that.

Most people who’ve studied human origins agree that there was some sort of expansion of the “first” modern humans, Homo sapiens, out of the the human star’s South and East African point somewhere between 50,000 and 150,000 years ago. These ancient African migrants may have used bone and ivory for tools, as well as the more usual stone and wood, although none of this actually shows up in the archaeological record till later (Curtis, Swisher and Lewin 2001). But evidence for a fairly advanced technology and a good coastal economy appears in South Africa sometime before 40,000 BC and possibly as early as 110,000 years ago (Stringer and McKie 1996). This economy presumably included the exploitation of riverbank and lakeside environments as well. More evidence of these people’s achievements will be uncovered as more research is done on this period in Africa.

But ancient migrations were presumably just as complicated as historic ones. And so, like all migrations mentioned in this case, this particular one is unlikely to have been a single movement by a single group of people. The Homo sapiens migration may have started as early as 150,000 years ago and carried on intermittently until 50,000 years ago (A look at European football teams, for example, reveals a more recent migration out of Africa). Interestingly the 150,000 year date provides a good fit with the mtDNA evidence and the 50,000 year date with the Y-chromosome (“MtEve” [The Trees]). The 50,000 year date also fits African “Extinctions” [What Have We Done?], and the defence suggested in Part IV that the distribution of Y-chromosome variants reflects the expansion of “Technology” [Progress]. Anyway these first modern humans, as shown by the “Kibish” skeleton from Ethiopia dated at up to 130,000 years ago, were actually much more heavily built than any humans are today (Stringer and McKie 1996). They also had a brow-ridge and a sloping forehead. Other more recent skulls from the region, dated at 120,000 years, show even more archaic features (Tattersall and Schwartz 2000). This shows that the human population of Africa at the time was extremely varied, and we have continued evolving since this migration (whenever it happened). These early Homo sapiens probably behaved much as we do today though. And any advantage they had could easily have been in their culture or technology, rather than in their genes. If so they would certainly have been able to breed with other human populations they ran into. But culture can sometimes obstruct gene flow (“Change” [Variation Through Time]).

Genes Again

At this stage it is very interesting to consider three more of the genetic maps presented in Cavalli-Sforza et al (1994). Cavalli-Sforza himself suggests that these three particular maps probably represent some ancient migration from Africa.

His map of the seventh principal component of human genes for the world shows a genetic extreme centred round the southern end of the Red Sea, in the regions known today as Aden and Ethiopia. A friend has suggested that perhaps there has been a spelling mistake and Adam and Eve lived in “the Garden of Aden.” There’s no harm in keeping old myths going. They often contain valuable lessons for us today. Remember, though, that this map represents just the seventh principal component for the world as a whole. The Aden genetic extreme in this world map weakens gradually across Asia and rapidly into Southern Africa.

We find the Aden pole of genetic variation, centred at the southern end of the Red Sea (this time in Ethiopia), in Cavalli-Sforza’s map of the third principal component for Africa. This variation grades to an opposite extreme in both Morocco and South West Africa.

Next, the fourth principal component for Asia again shows a genetic extreme centred round Aden in the southwest Arabian Peninsula, across the southern end of the Red Sea from Ethiopia. Its genetic opposite is centred east of this through India, and across much of central Asia as far as the Sea of Japan (map 15). The Indian extreme’s pattern also shows up to some extent on the world map.

Both the southern end of the Red Sea and the Persian Gulf must have been virtually dry land at the time. It looks as though the original migrations started when continuous land existed at either side of Saudi Arabia. There were ice ages, and presumably lowered sea level, between about 70,000 and 60,000 years ago, and again 30,000 to 10,000 years ago. In fact the jury will see that the maps actually make sense if interpreted as migrations between 30,000 and 60,000 years ago. We’ll touch on these migrations soon.

But the fact that there are two different genetic elements shows that the maps cannot be a product of any “first” migration. Another group of humans was already outside Africa. The defence suggested in “MtEve” [The Branches] that mtEve’s line might have left Africa long before Y-chromosome Adam did. It may have been these people who make up the Indian pole. But perhaps the genetic difference goes back to still earlier populations. Neanderthals were not present in India but other humans seem to have been there for a very long time. Where had they come from?

The Middle East

The evidence indicates (Cunliffe 1994, and Tudge 1996) that by about 90,000 years ago modern humans had reached the region the defence calls Canaan (see “Indo-Europeans” [The Chariot]). But the fossil evidence suggests that for the next 50,000 years Neanderthals occasionally return (Stringer and McKie 1996). The alternations between modern humans and Neanderthals seem to coincide with ice ages and relatively warm periods, with Neanderthals occupying sites during colder periods. Because Neanderthals had evolved in the cold climates of high latitudes and altitudes they were genetically adapted to cold conditions. Therefore these alternations are not surprising, but they show that technology and culture had not yet replaced biology as the main human adaptation to different environments. But modern humans in the region may have been eventually able to move into cooler regions once they had learned something cultural or technological off Neanderthals.

The two stone technologies in the Middle East at the time were very similar (Curtis, Swisher and Lewin 2001). In fact it is very difficult to determine whether any particular stone technology belongs to Neanderthals or to modern humans (Stringer and McKie 1996, and Tattersall and Schwartz 2000). Again this sharing of technology argues for contact and the possibility of some interbreeding, and against separation at the species level. Any hybrid zone was very narrow though. There is very little evidence the two groups crossed genetically and so we can presume that life was tough. As the defence has explained (“Change” [Galapagos Finches]), specialisation and tribalism are greatest at times of environmental stress.

In fact the technology used in the region did actually gradually change over time. And some workers do see a slight break with the development of the “Late Levantine Mousterian”. If your head is spinning already you can look back at the chart in “Technology”. The “Early Levantine Mousterian” culture, lasting in Canaan till around 60-70,000 years ago, presumably belonged to the first Homo sapiens to leave Africa 90,000 years ago. This Early Levantine Mousterian occurred mainly in the south, the Late Levantine Mousterian being more common in the north (Mellars 1990). This suggests that the Late Levantine Mousterian developed when incoming Neanderthals from the north combined their culture with that of the then resident modern humans. A hybrid zone formed and moved back and forth as the ice age progressed (Anthony Marks quoted in Mellars ed. 1990). The jury saw in “MtEve” [The Branches] that modern human mtDNA may have survived in such a hybrid zone. When the climate ultimately warmed again modern humans returned from the south, in turn adopting elements of this Late Levantine Mousterian. They developed the “Levantine Upper Palaeolithic”, and may have introduced Y-chromosome Adam’s line. The whole process was presumably similar to historical interactions between various groups of people in the region, and around the rest of the world, over the last few thousand years.

Lending further weight to this interpretation is Anthony Marks’ suggestion that, rather than developing from the Late Levantine Mousterian, the Upper Palaeolithic in Canaan seems to develop more from the Early Levantine Mousterian. This would be so if it were modern humans who were responsible for the Upper Palaeolithic. But the change doesn’t coincide with their first arrival. The Upper Palaeolithic in the region evolved gradually, and there’s a good possibility Neanderthals contributed to it (Smith et al 2005). Presumably the spread of this Upper Palaeolithic population into Europe via Turkey, along with more interrelationships with Neanderthals, gave rise to the Aurignacian of Europe. Back movement from Europe of this technology, if not of people, gave rise to the “Levantine Aurignacian.”

Interestingly a very simple reading of the mutations in human nuclear DNA indicates Europeans are basically a hybrid between Asians and Africans (Cavalli-Sforza et al 1994). Perhaps map 15 actually shows the expansions of two separate populations that eventually gave rise to the Aurignacian and Gravettian cultures of Europe. The movement across the Red Sea, centred on Arabia and Ethiopia, could be interpreted as a movement of the Cro-Magnons, who eventually developed the Aurignacian culture. The presence of Neanderthals in the Turkish Mountains slowed their expansion into Europe. The eastern, or Indian, genetic extreme might then represent an element of human expansion that moved onto the Russian Steppes and eventually produced the Gravettian culture.


The people who brought the Aurignacian into Europe, usually called Cro-Magnon, are often referred to as being “fully” modern-looking as though our evolution stopped at that point. It would be much more correct to say that Cro-Magnons were “essentially” modern. Cro-Magnons certainly looked different from modern Europeans. Regarding them Chris Stringer and Clive Gamble (1993) write, “But that does not mean, as is often assumed, that they were fully European looking: in fact they were physically unlike their successors of the last 10,000 years”. They were “robustly built and showing mixtures of ‘racial’ features which are nowadays found scattered across the populations of the world”. In other words the European population has continued evolving since Cro-Magnon times. Single origin supporters would say this evolution happened through genetic change within Europe, along with the genetic influence of later arrivals. Spread origin supporters simply suggest that much earlier inhabitants also contributed genetically. The Neanderthals became isolated from the main stream of Human Evolution ten times as long ago as did the Cro-Magnons, and so it’s not surprising we see ourselves as being ten times as different.

Chris Stringer and Robin McKie (1996) admit Cro-Magnons “had relatively smaller, flatter noses than either Neanderthals or modern Europeans”. They go on to say that Cro-Magnons “then evolved a nose that ended up looking like a Neanderthal or European one”. They suggest this happened by parallel evolution.

As a result of isolation, and the consequent inbreeding, Neanderthal numbers in Europe may have been quite low when Cro-Magnon humans with their Aurignacian culture were first able to move in. Cro-Magnons may have been moving into essentially unoccupied regions. And the slight warming 50,000 years ago would have given these incoming “modern” humans an ecological advantage over the cold-adapted Neanderthals. Certainly the Neanderthal population had fluctuated greatly over the period of their existence (Cunliffe 1994) and their numbers eventually became greatest in the areas of park tundra where the mixed cultures survived (Szeletian, Châtelperronian and Uluzzian, see “Neanderthals et al” [Aurignacian and Mousterian]). Anyway living was hard. There seems to be very little evidence of actual breeding between Cro-Magnons and Neanderthals in Europe at that stage.

The defence will later show (“North to Alaska” [The Gravettian]) that a separate group of modern humans, who had moved from India onto the Southern Russian steppes through what are today Iran and Afghanistan, developed the next European culture, the Gravettian. They too had been exposed to Neanderthal technology, culture, and genes. The expansion from India shown in map 15 may have been a mix of at least three technologies and cultures; a pre-existing Indian one along with a recently combined African and Neanderthal one introduced via what we know today as Iran. Three heads are better than one. We’ll return to the Aurignacian and Gravettian in “Culture” [Europe]. And the defence will use the information in map 15 again in map 19 (see “North to Alaska”).


If the expansion from the human star’s Indian sub-point followed the normal pattern it would have been the result of a new technology or culture introduced from somewhere outside the region. The hybrid of this technology and culture with any already existing would have allowed the population to exploit the environment in some new way, and led to a new wave of population expansion. Whatever this innovation could have been, wherever it came from, it was almost certainly similarly a product of previous migrations and mixing.

The climate from 190,000 to 130,000 years ago was particularly cold and sea level was presumably very low. Even the cold spell during the most recent ice age didn’t last as long as this, and so the earlier period seems to be an obvious time for an expansion across the Red Sea to have taken place. The very rapid warming about 120,000 years ago would have let humans move far to the north. The climate then slowly cooled again until by 75,000 years ago another ice age started. This was the shortest and least cold of the three ice ages covered in “Neanderthals et al” [Climate] but it’s almost certainly associated with the modern human expansion across Wallace’s line. The jury will soon see (“Into Australia” [Wallace’s Line]) that people needed some sort of boat to do that though.

There’s a possibility humans were then able to move along the Aleutian Island chain, and so into America, during the same period of low sea level. Interestingly Cavalli-Sforza’s (1994) map of the fourth principal component of worldwide gene distribution, although very complicated, does perhaps provide evidence for an expansion at some time from New Guinea into Asia. The defence feels it is not necessary to present the New Guinea map as further evidence in favour of the defendant because map 5 certainly indicates some sort of expansion from Southeast Asia. But, as the defence said in “Pacific Population” [Hoabinhian], the New Guinea expansion seems to have reached as far as Central America, some parts of South America and even into Africa. The surprising level of genetic variation found in South America is usually considered to be the product of a more recent series of “founder effects” (“Hybrid Vigour and Inbreeding” [Survival]). But an early settlement would also fit the evidence for apparent early human presence in South America. It does seem strange they left no evidence of their passing in North America though. Perhaps glaciated mountains had confined them to the coast until they reached Central America. The consequent inbreeding may account for their inability to reach high population numbers until other people arrived.

The defence mentioned in “MtEve” [The Branches] that some early branches of the mtEve and Y-chromosome Adam trees reached as far as Australia and New Guinea. Modern humans actually arrived in that region long before they had moved into Europe. In fact their arrival almost certainly pre-dates the migrations shown in map 15.

See next :: “Into Australia”

Witnesses Called

Cavalli-Sforza, Luigi Luca, Menozzi, Paolo and Piazzi, Alberto (1994) The History and Geography of Human Genes. Princeton University Press, New Jersey.

Cunliffe, Barry ed. (1994) The Oxford Illustrated Prehistory of Europe. Oxford University Press, Oxford.

Curtis, Garniss, Swisher, Carl and Lewin, Roger (2001) Java Man. Little, Brown and Company, London.

Mellars, Paul ed. (1990) The Emergence of Modern Humans. Edinburgh University Press, Great Britain.

Smith et al (2005) The Assimilation Model, Modern Human Origins in Europe, and the Extinction of the Neandertals. (PDF) Quaternary Intern. 137, 7-19.

Stringer, Christopher and Gamble, Clive (1993) In Search of the Neanderthals. Thames and Hudson, Great Britain.

Stringer, Christopher and McKie, Robin (1996) African Exodus. Random House, UK.

Tattersall, Ian and Schartz, Jeffrey H. (2000) Extinct Humans. Westview Press, New York.

Tudge, Colin (1996) The Time Before History. Scribner, New York.

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