Human Evolution On Trial By Terry Toohill: Human Evolution On Trial

Human Evolution on Trial - Neanderthals et al

Presumably because they lived in Europe Neanderthals are the most intensively studied of the Archaic Homo sapiens species (Stringer and Gamble 1993). In fact their distribution was basically originally centred on the point of the human star the defence calls Northwest Europe (see map 13), once again at a geographical extremity of the human range. Not surprisingly even within this region the most extreme form of Neanderthals were found at the western extremity (Tudge 1996, and Stringer and McKie 1996).

Neanderthals were more compact, stocky and muscular with shorter limbs and bigger brains than are modern humans, a product of the ice age (Stringer and McKie 1996). Everyone agrees they all looked much the same as each other, *(but see abstract of this paper) probably inbred through intense selection. They first appeared about 150,000 to 130,000 years ago. Earlier fossils from Europe dated before then at more than 200,000 years are, like Australopithecus, Homo habilis and Homo erectus, very variable (Stringer and Gamble 1993). Some individuals could be included in the Neanderthals because they look very similar to them.

But this would mean that within the same population there were at least two separate species. And so these particular fossils are considered to be too old and are usually included in the species, or subspecies, Homo heidelbergensis. Again the name change depends on where you draw the line in time rather than the fossils’ appearance. The main disagreement within students of human origins, though, is whether or not Neanderthals have contributed genes to modern human populations.

No Neanderthal mtDNA lines are found in modern humans. Some people have suggested that a change in chromosome numbers may have separated modern humans and Neanderthals, but there is no evidence for this. And even if true the defence pointed out in “Hybrid Vigour and Inbreeding” [Hybrid Vigour] different chromosome number doesn’t necessarily indicate inability to produce fertile offspring. Other explanations for the evidence are necessary (“MtEve” [Interpretation]).

I suggested in Part II that New Zealanders could eventually evolve into a new race through the combination of their European and Polynesian ancestry (“Change” [European Migration]). I showed that in turn the Polynesians had evolved from a combination of people from two different points of the human star, East Asia and Australia (“Pacific Population” [Mixing]). In Part V the jury will see that all modern humans are a product of combinations of ancestors. Is it possible this willingness to form hybrids has developed only since we became “modern”? Unlikely. The defence has shown throughout Part IV that hybrid formation seems to have happened as far back as we can follow our ancestry. In Part III we saw the same process is probably even involved in the evolution of many kinds of birds, plants and animals.

Two From One

Neanderthals and modern humans almost certainly both evolved from just a single species: Archaic Homo sapiens or Homo heidelbergensis. So this is a convenient point to pause and remind the jury of how separate races, kinds and species develop in the first place.

Members of the prosecution often demand to know how it is that separate species can arise through the sudden development of complex structures? The quick answer is that they don’t. In “Hybrid Vigour and Inbreeding” [The Wave Theory of Evolution] the defence explained how any factors (including tribalism) that divide populations and limit gene flow within any particular species lead to divergence within that species. The defence has also shown (“Species” [Difference]) that different species can simply arise if geography isolates populations. The population in each region changes in its own direction. Once two populations cease to exchange genes genetic drift alone could eventually lead to mutually incompatible genes. But Galapagos finches at least, as the jury saw in “Change”, can separate or come together depending on the environment.

New species may arise rapidly if selection within their particular environment is great and leads to significant inbreeding. But the evidence shows that any new characteristic still arises in a straightforward manner. For example some birds classified as ducks don’t even have webbed feet. All birds have some webbing between their toes though and a single genetic change may be responsible for letting the webbing become larger. The environment may have encouraged rapid selection towards more complete webbing but it would also keep extremes from developing. And most ruminants have their horns at the top of their head, but in cattle and bison the horns are at the sides of their head. To help me construct the earlier diagram of ruminant evolution I took the liberty of assuming the variation in horn shapes developed through a series of intermediate forms (such as gnu and African buffalo) with bosses on their heads. I used the idea that this eventually changed the base of their horns. Mutations in a single gene could have been responsible for this change too.

Species that occupy a wide geographic range can develop into separate kinds or species at the extremities of that range (“Evolution” [Geographic Speciation]). The jury saw in “The Human Star” that groups at various margins of even the modern human distribution look different to people at other extremes. This seems to be the most likely explanation for the separation of Neanderthals from modern humans. Had they become separate species? It seems that at least technology crossed the boundary between them at times (Smith et al 2005).

Climate

Changes in the earth’s climate over the last two million years have always been important for our evolution. The defence will cover just the last 200,000 years though, because this is enough to explain the present distribution of humans and it covers the period of the Neanderthals. Diagrams showing the oxygen isotope curves obtained from deep-sea cores are given in many publications (for example Stringer and Gamble 1993, and Cunliffe 1994). They reveal the following.

Around 200,000 years ago the earth had again become about as warm as it is today. Once more a cool period developed and by about 185,000 years ago another ice age set in. This lasted until about 130,000 years ago. There was then a very rapid warming and temperatures rose to probably a little warmer than they are today, roughly speaking. The peak temperature occurred about 120,000 years ago and then another period of cooling set in. Temperatures fluctuated downwards until another ice age set in nearly 75,000 years ago, probably helped by a volcanic eruption, Mount Toba, in Sumatra (Wade 2001). Temperatures basically remained fairly low but rose slightly about 60,000 years ago with a small peak at 50,000. From 30,000 years ago they fluctuated downwards again until the depth of the last ice age about 18,000 years ago. From about 13,000 years ago the climate warmed rapidly, then cooled again. In the last 10,000 years the climate has been much the same as at present but with minor fluctuations and mini ice ages.

The three extremely cold dry periods during the last 200,000 years were each significant for Neanderthals. The defence will suggest next in “MtEve” [The Branches] some of these changes might also have contributed to cultural developments in Africa. First of all the jury can see that Neanderthals developed during the cold period that started 185,000 years ago. Within the human star’s Northwest European point they remained undisturbed for the next 150,000 years.

Neanderthals seem to have expanded east and south into western Asia during the coldest phase of the next ice age around 70,000 years ago. They had become thickset and genetically adapted to cold conditions and were able to move into environments vacated by other groups of humans as the climate cooled. We’ll return to the situation in the Middle East during this cool period 70,000 years ago in “Out of Africa”. But you can see from looking at map 13 that by then modern humans were effectively not able to get anywhere outside Africa without passing through territory already occupied by Neanderthals.

During the slight warming before the most recent ice age Homo sapiens or “early modern humans” (Cro-Magnon) with Upper Palaeolithic “Aurignacian” culture*(see also - pdf) started moving into Europe and seem to have slowly replaced Neanderthals. By the depth of the most recent ice age the Neanderthals were gone. But Neanderthals and modern humans had lived separately but side by side in Europe for perhaps as long as 10,000 years (Wade 2001). The fact they basically remained separate for several thousand years indicates life was tough. Specialisation and separation are greatest during times of environmental stress.

Aurignacian and Mousterian

The Neanderthals’ stone technology is called “Mousterian” and at least three cultures in Europe do in fact indicate a mixing or hybrid between the resident Mousterian and the Upper Palaeolithic Aurignacian, brought in about 35,000 years ago by these Cro-Magnon or early modern humans. There is abundant evidence of the development of the hybrid technologies is best explained as populations of Neanderthals in more isolated, mountainous or northerly regions (up to 50° north) holding on after modern humans had expanded into Europe, and then adopting at least some incoming technology (but see D’Errico 2003). Perhaps over the 10,000 years they adopted some incoming modern human mtDNA and Y-chromosome lines as well.

Is it likely technology could have been exchanged without some gene exchange? Sure, culture and technology travel faster than genes. Ultimately genes from these three hybrid cultures may have been extinguished (Smith et al 2005) but cultural exchange can hardly be possible without some social interaction. Any children may have been infertile when adult if Neanderthals and Cro-Magnon were, in fact, different species but the cultural interchange implies a closer relationship than that between groups as different as horse and donkey.

The outline in map 14 is the Cro-Magnon or Aurignacian boundary (Cunliffe 1994). The hybrid or mixed technologies lie within the boundary. They are: number 1 the “Châtelperronian” in France, 2 “Uluzzian” in the north and south of Italy, and 3 the “Szeletian” in Hungary, Slovakia and southern Poland (Clark 1969, Stringer and Gamble 1993, and Cunliffe 1994). Neanderthals also survived for a long time in both Spain and in parts of the Balkan peninsular. Tools from the Aurignacian culture are shown at the bottom right (Roe 1971). Tools from the Neanderthal Châtelperronian are shown in the upper left (also from Roe 1971). The modern human and Neanderthal skulls are once again from Johanson and Edey (1982). I drew the heads myself.

When the Aurignacian arrived in Southern Europe the climate was a little milder than it later became. Boundaries of the various vegetation zones were probably much the same as they were later at the height of the ice age though. The map of European vegetation zones during the ice age as shown in Cunliffe (1994) shows the three hybrid cultures survived in areas that have been called “park tundra”. This park tundra was a mosaic of trees and open grass and herb fields. It was probably the coldest environment and the furthest north humans were able to occupy before they had clothes. The Aurignacian people were confined to slightly warmer regions. Different genes rather than technological developments were still the main adaptation to the environment. Presumably some sort of hybrid zone existed at the boundaries between the two groups. Around 27,000 years ago a different Upper Palaeolithic technology, the “Gravettian”, expanded into Europe from the east, via the still colder steppe vegetation zone (Temperate Zone grassland). The defence will show in “North to Alaska” [The Gravettian] that by then humans had warm clothes. The three Neanderthal hybrid cultures disappeared with the Gravettian’s expansion but they may have been absorbed rather than exterminated (Marcel Otte quoted in Mellars 1990). The Gravettian was expanding into environments humans had been unable to exploit until then. During times of plenty the boundaries become porous. Interestingly the jury will see much later in “Culture” [Europe] that a map of European genes (map 18), although independently derived from modern human genetic evidence, shows a similarity to the pattern in map 14.

Steve Kuhn (quoted in Wright 2002) has suggested interactions between Neanderthals and early moderns was responsible for the flowering of Upper Palaeolithic culture in both groups. In other words the exchange would not have been all one way. The modern humans of both the Aurignacian and Gravettian had acquired important technological advances from the Neanderthal Mousterian.

Technological hybrid vigour.

By the time they arrived at the human star’s Northwest European point the varied modern human technology was probably already the result of contact with different Neanderthal technologies during their expansion. The incoming cultures certainly used bone, ivory and antler more than the Mousterian did (Cunliffe 1994). Neanderthals may not have used these materials at all (Cavalli-Sforza 1995) but the Châtelperronian tools shown in map 14 suggest Neanderthals may have been better at stone technology. Eventually the combined technology enabled humans to move north of 50° latitude. We will come back to this in “North to Alaska”.

Superiority

Many people believe the evidence shows modern humans replaced the Neanderthals because we brought in a superior culture and were more intelligent. Chris Stringer and Robin McKie (1996) for example suggest the Neanderthals of the Châtelperronian were able to learn to make more sophisticated tools only after contact with incoming modern humans. But you have to learn any new technology. How many parents have to get their children to show them how to use some new appliance? Besides it still implies a closer contact than merely watching newcomers from across the valley. It implies quite intimate contact.

Although there is no doubt Neanderthals ate a lot of meat, Stringer and McKie also present evidence showing they were not such efficient hunters as the incoming humans. Anyone who has been hunting knows it is a complicated business, even with a shotgun or a rifle. We, along with most predators, have to learn how to hunt. Even domestic cats have trouble working out how to kill their prey. Wild cats learn how to kill from their parents (Tudge 1996), *(see also) New hunting methods were obviously transmitted by example in Neanderthal times. You couldn’t learn it from a book, or off the Internet. The Neanderthals’ more basic hunting ability (although see D’Errico 2003) in no way necessarily proves a less intelligent population.

Beliefs in the superiority of modern humans over ancient humans such as Neanderthals are frighteningly similar to those used to justify more recent European replacement of indigenous inhabitants. I hasten to point out that I don’t believe for a moment that either Chris Stringer or Robin McKie for example support white supremacist ideas. I’d be surprised if many anthropologists do. But old mythconceptions die slowly. Perhaps the wish to deny any contribution of Neanderthal genes to modern humans derives from biblical ideas of the special, sudden, single origin of each species, including the modern human species.

Neanderthals actually had larger brains than do modern humans (see for example Tudge 1996, and Jones 2001). They also had a much larger nose than did other contemporary populations, probably evolved as an adaptation for warming cold air before it reached their lungs. In fact Stringer and McKie (1996) admit their noses were “somewhat similar” to those of modern Europeans. Another Neanderthal characteristic considered different to modern humans is the bulge at the back of their skull, called the “occipital bun”(or "chignon"). But many modern people of European extraction have a similar, if smaller, bulge. Neanderthal skulls also show a more rounded profile when viewed from behind than do those of most modern humans (Stringer and Gamble 1993). But modern European skulls are more rounded than are Polynesian skulls for example (Houghton 1980).

Some people claim that a child’s skeleton discovered at Lagar Velho in Portugal, dating from 25,000 years ago during Gravettian (pdf) times, shows a mix of Neanderthal and modern characteristics; but others say it is quite within the modern human type (Wright 2002). Some fossils of early modern humans in Central Europe could also be interpreted as being hybrids between Neanderthals and modern humans (Smith et al 2005, and Stringer and Gamble 1993).

Single origin supporters explain continuities in the physical appearance of regional populations, such as large European noses and those mentioned in “Species or Not” [East Asian Point], as being the result of parallel evolution. They say that more recent populations in a particular region were subject to the same selection pressures as earlier ones and therefore developed the same characteristics. This may account for some similarities but is unlikely to account for them all. It is also unlikely more recent populations were subject to the same selection pressure. Climate has fluctuated greatly during the last two million years.

Talking of climate we know Neanderthals evolved and lived for more than 100,000 years in regions of winter snow. Therefore it is virtually certain they would have been blond-haired with white skin. Although I have seen this mentioned several times in articles about them I am yet to see any artist’s portrayal of Neanderthals that so much as even hints at it. They are usually portrayed with black hair and darkish skin. Perhaps artists feel the implications are too much for many people to accept.

In fact there are conflicting ideas as to whether Neanderthals could actually blend into modern human society. It used to be said that if he had a wash, shave and put on a suit a Neanderthal man could sit on a bus and no one would notice. These days the fashion is to emphasise the difference. How long will it be before the wheel turns and Neanderthals are back on the bus?

See next :: Mitochondrial Eve

Witnesses Called

Cavalli-Sforza, Luigi Luca and Cavalli-Sforza, Francesco (1995) The Great Human Diasporas. Addison- Wesley

Clark, Grahame (1969) World Prehistory. Cambridge University Press, UK.

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

University Press, Oxford.

D’Errico, F. (2003) The Invisible Frontier: A Multiple Species Model for the Origin of Behavioral Modernity. (pdf) Evol. Anthrop.12, 188[-202.

Houghton, Philip (1980) The First New Zealanders. Hodder and Stroughton, Auckland.

Johanson, Donald and Edey, Maitland (1982) Lucy. Warner Books, New York.

Jones, Martin (2001) The Molecule Hunt. The Penguin Press, London.

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

Press, Great Britain.