Assimilation or replacement - a study about Neanderthals and modern humans

Contents

1. Introduction

2. Description and comparison of the two main characters
a) Morphology
b) Cultural abilities
c) Dispearsal areas
d) Time span of existence

3. Who was the last common ancestor of Neanderthals and modern humans and where did he live?
a) Genetic evidene
b) Fossil record

4. Description of the main issue
a) Presentation of the four hypothesis concerning the transition from H. ergaster/erectus
to Homo sapiens
b) Integration of “assimilation” and “replacement” into these models

5. Molecular/genetic research.
a) mtDNA comparison of Neanderthal fossils, modern human remains and current
modern humans

6. Archaeological and palaeontological research
a) Comparison of the morphology of skeletal remains of different ages and parts of the
world
b) Comparison of the cultural remains of different ages and parts of the world.

7. Simulation studies.
a) What are they based on?
b) What are the results?

8. Conclusions

9. References

1. Introduction

The Neanderthals lived in Europe and the Near East for at least 250,000 years and they outdared several climate changes. They were capable of surviving in a harsh, cold environment and were well adapted to it – cultural and morphological. Thus, the Neanderthals have been proven to be a successful human kind. But why then did they disappear so quickly and without a trace just between 40,000 and 28,000 yr BP (= years before present) [8]?

One possible answer is that modern humans starting to invade the Near East and Europe out of Africa 45,000 to 40,000 yr BP have outcompeted them, due to higher cultural and mental abilities, using the resources in a more efficient way than the Neanderthals. But is this really true? Have modern humans really had higher abilities? Did they admix with the local Neanderthal populations, integrating the native genes in their gene pool? Or did modern humans not interbreed with them?

And – the big question: were Neanderthals and anatomically modern humans distinct species or just local variants of the same species?

To bring more light into this scenario, these questions will be answered in the following chapters using genetic, morphological and simulation-data that has been brought up by several researchers over the last years.

Answering these fundamental questions also lies in the range of basic needs of human mind: we all want to know where we come from, who was our ancestor and who was it not. To realize which strange ways evolution sometimes takes and to determine what really happened is for sure an exciting thing, and that is exactly what researchers do when they trace human evolution back to the point when Neanderthals and modern humans met in Europe during the last ice age. Only one of them should survive this meeting, and to determine why and how this happened I will start with the description and comparison of the two main characters.

2. Description and comparison of the two main characters

a) Morphology:

A typical Neanderthal man was of short figure - around 160 or 165 cm. There was quite a strong sexual dimorphism as Neanderthal women were around 10 % smaller than men.

In particular the legs were very short compared to the upper part of the body which also showed an enlarged rib cage. This is due to large lungs that made a Neanderthal breathe efficiently. Neanderthals had heavy bones that were very thick and thus quite resistant to mechanical disturbance. They had short thick fingers and arms. Also, the cranium was robust showing thick prominent brow ridges and a flat shape, in particular a low forehead. The face was projecting with a big nose and chinless. The back of the skull showed an occipital bun. Over all, the cranial capacity was very large – the average is around 1500 ccm, but an individual with even around 1800 ccm has been found. From the bone morphology can be deducted that Neanderthals were very muscular and thus weighed a lot compared to their size (around 75 kg at 165 cm). Thus, the typical morphology of a Neanderthal shows a strong adaptation to the rough cold climate in Europe during the ice ages and can be characterized as an extreme sprinter [3], [5].

A typical anatomically modern human is and was taller – with an average of 180 cm today – and shows less sexual dimorphisms as modern human women are around 7% smaller than men. He has quite long legs and a small rib cage. He possesses light, more gracile bones and longer, thinner fingers and arms. The cranium is more gracile in general and has strongly reduced brow ridges. The skull shows a high forehead and is more round in general showing no occipital bun. The face is not projecting with a smaller nose and shorter jaws. It shows a chin. The cranial capacity is large, but not as large as the Neanderthal one: the average is around 1400 ccm. The body is not very muscular and – at least for primitive people – the weight not that great compared to the size. Anatomically modern humans are thus not well-adapted to cold climates but rather to temperate or subtropical climates and can be characterized as generalists or long-distance runners [3], [5].

b) Cultural abilities:

The Neanderthals were no primitive, culture-less people. In fact, they probably had a language indicated by a fossil hyoid showing strong similarity to ours. Especially the hole for the nerves controlling the tongue is as big as ours suggesting that the tongue’s flexibility was very high. Anatomic studies show that the larynx was built the same way as ours. All these features would make no sense unless it gave the Neanderthals the advantage that language and effective communication offers. This advantage far outweighs any disadvantages of spending resources on developing such an anatomy and the added danger of choking. Also, Neanderthals had a highly developed weapon culture, ranging from hunting spears with stone tips to scrapers and hand-axes. Neanderthals were able to use fire and wore clothes that they made from the skin and fur of their prey. They lived in caves and sometimes built small temporary housings. They had a strong social company which is indicated by fossils that show heavy but healed bone-injuries and old people without teeth that were fed by younger group members. Neanderthals were also used to spiritual thinking as they buried their dead in special places with elaborate burial objects like flowers and decorated tools. Thus, they were a folk with both culture and tradition [12].

Anatomically modern humans had all the abilities mentioned above but they had some additional cultural achievements. These were in particular the development of abstract art (cave paintings, music instruments, pearl chains out of shells and the abundant use of red ochre) and better hunting weapon and tool technologies (complex bone technology and multiple-component missile heads). Good examples are the approximately 30,000 year old ivory flute from Germany, the perforated snail shells from Blombos Cave in South Africa which are about 77,000 year old or the cave paintings from Chauvet, France, that are about 30,000 years old [8], [13]. All these things show that perhaps they had a spiritual advantage over the native Neanderthals. Thus, anatomically modern humans show an advanced status of cultural level compared to Neanderthals.

This difference perhaps stems from the better conditions that anatomically modern humans found in the subtropical Africa whereas Neanderthals, although perhaps capable of these things, just didn’t have the adequate environment to realize them. Another possible kind of view is that anatomically modern humans had a more flexible mind giving them these cultural advantages, maybe because they were not extremely adapted to a harsh environment and thus not “programmed” to just survive like the Neanderthals. Today we cannot distinguish whether the first or the latter conclusion is right because we unfortunately cannot test a Neanderthal’s ability to perform art. Additionally, some artefacts that were found and are associated with art cannot clearly be assigned to modern humans and might be due to Neanderthal art [1]. Also, there is evidence that Neanderthals started manufacturing art when they started to get in contact with anatomically modern humans [8]. Whether they just copied it without understanding it or whether they got the spark and started doing it themselves is not distinguishable today.

c) Dispearsal areas:

The Neanderthals occupied primarily South-Western, Middle and South-Eastern Europe, but fossil finds indicate that they were also present in the Near East [8].

The first fossils of anatomically modern humans were found in South and East Africa, but they soon spread over North Africa to the Near East invading Europe and Asia. Later on, Australia and the American continent were colonized by them. During this population movement process all other archaic human populations like the Neanderthals or Homo erectus disappeared all over the world [8].

d) Time span of existence:

The first skeletons with some Neanderthal features are about 300,000 years old. Later fossils, especially from 150,000 yr BP on, show all characteristic features of a typical Neanderthal and thus mark the beginning of existence of this human form in Europe. The last typical Neanderthal skeletons are 28,000 years old and have been found south of the Ebro valley in Southern Spain. This fossil evidence shows that this group must have died out around that time. Thus, Neanderthals and Neanderthal-like humans have existed for at least 250,000 years which indicates that they were a successful human form [12].

The oldest anatomic modern human fossils were found in Ethiopia and are dated back to 160,000 yr BP [8]. This old Homo sapiens sub-group is called Homo sapiens idaltu [13]. Anatomically modern humans exist until today.

3. Who was the last common ancestor of Neanderthals and modern humans and where did he live?

a) Genetic evidence:

Several mitochondrial DNA (mtDNA) analysis of Neanderthal fossils, Cro-Magnon fossils and current modern humans have shown that the last common ancestor of both Neanderthals and modern humans must have lived between 365,000 and 853,000 yr BP with a best estimate of around 610,000 yr BP [10].

b) Fossil record:

My favourite theory is that the last common ancestor of Neanderthals and Homo sapiens lived close to the time of Homo antecessor and was closely related to this species. A fossil of this species has been found in the north of Spain and its age is estimated of around 780,000 to 980,000 years. This specimen shows features of both anatomically modern humans and Neanderthals and lived close to the virtual common ancestor that was suggested by the mtDNA analysis mentioned above. Thus, this species might be the ancestor of the last common ancestor or even be the last common ancestor of the Neanderthals and modern humans. Another skeleton that has been classified as this species has been found in North Africa and thus supports this theory because H. antecessor seems to have existed both in Europe and in Africa – the two potential emergence locations of the Neanderthals and modern humans [4].

Other theories suggest that Homo heidelbergensis which was first found in Mauer, Germany, was the last common ancestor. H. heidelbergensis lived around 600,000 yr BP [14]. However, at least for the European version of this species this theory seems to fail because the German H. heidelbergensis shares lots of traits with the Neanderthals and H. antecessor, and is thus likely to be directly descended from H. antecessor heading to become a Neanderthal. Also, other specimens of this species are found in Europe and this fact supports the theory that the European H. heidelbergensis is an early ancestor of the direct ancestors of the Neanderthals that are sometimes called pre-Neanderthals. On the other hand, the African H. heidelbergensis seems to be slightly different from his European kinship. He has less Neanderthal-like features and seems to be a missing link to the later arising species H. sapiens [12].

The African H. heidelbergensis and several other fossil finds which are located in Africa and fall roughly into the period of 600,000 to 200,000 yr BP are widely summarized in the species-collage “archaic Homo sapiens” and sometimes called “late Homo ergaster/erectus”. It is likely that anatomically modern humans are descended from one of these “archaic Homo sapiens”-populations who lived in Africa and that their ancestress was probably H. antecessor. The development from these archaic forms to H. sapiens was slow but steady (later fossils of this collage show more modern traits than older ones) indicating good living conditions in Africa and therefore a good environment to develop big brains and all other complex features that current humans call their own [12].

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