The study of human origins has been one of the most contentious areas of anthropological research for well over one hundred years. As in other debates of biological and cultural origins in human prehistory, the polarization of opinion into camps seeking to explain change through in situ evolution or through diffusion takes the headlines, and more moderate views take a back seat. The Upper Paleolithic transition in Europe is a particularly interesting time period in human prehistory, as there is a shift from the populations of Neanderthals with Middle Paleolithic technology to modern Homo sapiens and a more complex Upper Paleolithic technology.
The debate over the fate of the Neanderthals and the ancestry of modern populations has its origins in two different views of biological change: the catastrophism of French paleontological tradition and the evolutionary explanations of late 19th century biologists. The modern progeny of these evolutionary viewpoints is the Out of Africa II model that was first coherently argued in 1975 by Protsch von Zieten (Protsch 1975) and subsequently championed by C.B. Stringer, and the multiregional model proposed in 1943 by Franz Weidenreich (Weidenreich 1943a) and subsequently championed by C.L. Brace and M.H. Wolpoff.
At the heart of the debate is whether modern H. sapiens originated from a small African population from 250 kyr to 100 kyr ago that spread out across the globe rapidly displacing indigenous populations, or whether indigenous hominid populations are represented in modern regional populations. In essence, this is a debate about evolution and diffusion. Neanderthals and Europe have a special place in this debate for several reasons. First, the Feldhofer find of a Neanderthal was the first non-modern hominid recognized by palaeontologists, and therefore the issue of the Neanderthals and Europe has had a long history to develop.
Second, many important regional populations and fossils are not as prominent in the Western world due to the lack of access to the relevant research in non-European languages (i.e. the Jinniushan and other Middle Paleolithic Chinese material), and so the most accessible information predominates in the debates in Western academic circles.
Third, there is a Eurocentric bias in terms of the desire by some to have the origins of modern human behaviour and biology be placed in Europe. Fourth, there is also a bias to not have the origins of modern Europeans placed in Europe with the Neanderthals since the Neanderthals are so “primitive” looking in the minds of the observers and the public. Finally, there is a heated desire to sidestep any accusations of religious fundamentalist beliefs driving the theory, or racial discrimination driving the theory on both sides of the debate, and can be seen in the accusations bandied about by proponents of one side against the proponents of the other.
In the following paper, I will outline the origins of the main theories regarding the fate of the Neanderthals and the origins of modern H. sapiens, their progression through the 20th century along with the progression of new fossil finds, new dating techniques, new theories, and new interpretations of old data and assumptions. The overview will begin with an introduction to the arguments and their various spin-offs and include the criticisms levelled against these arguments at various times. Following the historical overview of the debate, I will discuss several lines of evidence as they exist to date, including the fossil record, the archaeological (behavioural) record, and modern genetics. The paper will conclude with a synthesis of the information presented in the paper and draw a conclusion about which theory is currently best supported by the evidence.
The current most accepted scenario for modern human origins has swung to the replacement model of Out of Africa II. The theory is called Out of Africa II to indicate the movement of a founding population of modern humans out of the African continent and to differentiate it from the well-accepted concept of the radiation of early Homo out of Africa nearly two million years ago. The historical origins of this type of model (furthermore referred to as “replacement” in this paper) that directly relates to Europe and the Neanderthals can be traced to several causes.
First, original descriptions and conclusions are always the hardest to leave behind, and this is particularly true of the Neanderthals. In 1872, Rudolf Virchow, published a report on the Feldhofer find that characterized it as a pathological modern human only a few centuries old (Virchow 1872). Since no dates were known for the find at the time, and a presumed ancient modern human fossil was already known that differed much less from the modern form (Broca 1868), Virchow’s view was thought to be supported based on the assumption that the individual was elderly, and that no human could live to such an age in a nomadic or hunter-gatherer society (Potonie 1958: 277). Neanderthals were excluded from the ancestry of modern man and remained so in the minds of most individuals for a long time.
Second, the most spectacular and important Neanderthal finds of the early 20th century occurred in France, and include Le Moustier in 1908 (Hauser & Klaatsch 1909), La Chapelle-aux-Saints in 1908 (Boule 1908), La Ferrassie in 1909 (Capitan & Peyrony 1909), and La Quina in 1911 (Martin 1911). By a series of chance events (the delays in the description of and incorrect reconstructions of the Le Moustier specimen, the trusting of La Ferrassie to M. Boule when he was preoccupied with the La Chapelle find, and the simultaneous release and subsequent overshadowing of the la Quina material by the La Chapelle remains), the La Chapelle-aux-Saints specimen became the de facto type specimen for the Neanderthals.
This was an unfortunate event for the status of Neanderthals in human origins, due to the biases of Boule, the acceptance of his work as the definitive description of Neanderthal traits, the pathologies associated with the specimen that became a part of its anatomical description, its status as the most “Neanderthal-like” of any specimen attributed to Homo neanderthalensis, falling at the extreme end of variation seen in the Würm Neanderthals (Wolpoff 1999: 682), and the conclusions Boule reached about the Neanderthals.
Boule characterized the Neanderthals as brutish, shuffling, creatures of limited intelligence more closely related to apes than man (Johanson & Edgar 1996: 224), and this characterization served as the basis for a century of journalistic caricatures of “cavemen”. However, what Boule either did not realize (or ignored) was that the specimen was extremely pathological with extensive arthritis and bone pathology. This specimen that became the “typical” Neanderthal, is probably one of the most atypical Neanderthal specimens.
At this time, established the view that Neanderthals could not be the ancestors of modern humans, and put forth three points to support this conclusion:
Modern forms of man already existed at the same time the Neanderthals existed, making it impossible for the latter to be ancestral to the formal.
The indigenous Mousterian lithic technology was replaced so rapidly by the Upper Paleolithic industries, that the Upper Paleolithic must have developed elsewhere over a long period of time before being brought into Europe.
The anatomical differences between Neanderthals and modern humans were so great as to preclude the possibility of in situ evolution. (Boule 1913)
It is interesting (and important) to note that while the material and sites Boule used as evidence to support his contentions have been shown to be inadequate or misinterpretations of the evidence, the idea of complete replacement of Neanderthals by modern humans continued on, being refined more and more and in far different ways than Boule would have imagined. Boule’s explanations of total replacement have their philosophical roots in the catastrophism of Cuvier in the early 19th century (Cuvier 1834), which is not unexpected since Boule was trained as a palaeontologist in mid-nineteenth century France where anatomy, geology, and paleontology were taught by Cuvier’s disciples (Brace 1964: 5).
To support his theory or replacement, Boule attempted to show that the morphological gap between Neanderthals and modern humans was so large, and the spatial gap between them so small, the only possible explanation is a replacement on one with the other. In his attempt to place Neanderthals away from the human lineage, Boule claimed many features that subsequent research showed to be completely false (Brace 1964: 5), and thus Boule’s presapiens theory has been relegated to paleoanthropology’s dustbin.
From the time of Boule up until the 1960s, the status of Neanderthals as a relict population with no place in the ancestry of modern humans was accepted almost universally by Western paleoanthropologists, and very little occurred to sway this opinion, even though the idea of the uniquely Neanderthal morphology as too different to be related to modern humans was abandoned (Clark 1955: 45) as a primary reason for Neanderthal displacement, and the specimens used as evidence that modern humans lived contemporaneously with or prior to the extinction of the Neanderthals continued to fall and be replaced by new candidates of ancient human specimens.
For example, these specimens were used as proof of the ancient status of modern humans (Brace 1964: 11):
Boule 1908 – Grimaldi
Boule 1913 – Grimaldi and Piltdown
Keith 1915 – Galley Hill
Osborne 1919 – (no evidence provided)
Osborne 1922 – Piltdown
Hooton 1931 – Piltdown
Howells 1944 – Mount Carmel and Swanscombe
Hooton 1946 – Piltdown, Galley Hill, and Swanscombe
Le Gros Clark 1955 – Swanscombe and Fontéchevade
Boule and Vallois 1957 – Fontéchevade
Montagu 1960 – Swanscombe and Fontéchevade
Not one of these specimens/sites has held up as being either a modern human or a modern human living contemporaneously or prior to the extinction of the Neanderthals. The fact that there are many such examples that have been found in the last 30 years does not make up for the fact that the replacement theory was supported by faulty evidence for most of its existence as a theory pertaining to the Neanderthals.
The late 1970s and early 1980s saw a new emphasis on the replacement model of modern human origins, first with the “African Origins” hypothesis proposed by Protsch (1975) which detailed the claim that modern humans first evolved in Africa and then spread throughout the rest of the world. Later, this was developed into the “Afro-European sapiens” hypothesis of Bräuer (1984), with more dates, specimens, and specific explanations added, which expanded the claim that the modern form had first evolved in Africa. This idea of the modern human form evolving first in Africa was melded to the concept of this form invading and completely replacing indigenous forms (Stringer & Andrews 1988).
The new emphasis on the replacement theory was due mainly to increased technology for genetics research and the early implications that all modern humans had a recent origin. Since the late 1980s, the preponderance of evidence used to support the replacement model with regard to Neanderthals has focused on two points: the genetic evidence indicating a recent common ancestor for all modern humans, and the idea that there was a behavioural divide between Neanderthals and Upper Paleolithic humans that gave the incoming Africans an edge in a competitive atmosphere and prevented the interbreeding of the two populations.
The opposing multiregional view of human evolution (furthermore referred to as “continuity” in this paper) can be traced back to Ales Hrdlicka. While Gustav Schwalbe was the first to espouse a linear sequence linking Neanderthals with modern humans (Schwalbe 1906: 25), he abandoned his stance in 1913 with the release of Boule’s work on La Chapelle (Schwalbe 1913).
It is in important to note his early view, however, as it influenced his then student, Franz Weidenreich (Brace 1964: 15). In 1927 Hrdlicka presented his full argument against Neanderthal replacement in his Huxley Memorial Lecture (Hrdlicka 1929) and repeated again in 1930 (Hrdlicka 1930). Hrdlicka viewed human evolution from a biological perspective of adaptation to selective pressures and did not see adequate reasons why the Neanderthal population would have been replaced on the basis of selective pressures.
He noted several problems (problems at this point in time) with the prospect of Neanderthal replacement by modern human forms:
Successful invasion and replacement of an established population presupposes a large invading population, and a large invading population requires a still larger mother population elsewhere.
Differential rates of evolution for postulated different human groups need to be justified. Why would one group (the European Neanderthals) cease to evolve with every form different from the set Neanderthal “type” be considered from a separately evolving superior population?
If population replacement did occur by a differently adapted population, why did they take over precisely the same sites that were used by the Neanderthals? Why did the supposedly superior population live basically the same life as the Neanderthals, with most of the technological revolutions occurring in situ? What examples can one give from contemporary history where one human group completely replaced another with the complete loss of the genetic variation from the replaced population (i.e. without inbreeding)? (Brace 1964: 13-14)
Since Africa is generally considered the source of Pleistocene hominid evolution the first point may seem to be unimportant. However, it is of major importance as it brings up the point of why migration occurs in populations. Migrations tend to occur with shifts in ecology, or with population pressure. In the case of non-human hominids, the only good explanation of why populations expanded all across the Old World is population pressure.
If there is population pressure that led to the spread of humanity all into Europe by at least 800 kyr ago and to the Far East by 1.6 myr ago, it stands to reason that by the Upper Paleolithic there would not be appreciable differences in population density from region to region in similar environments and contiguous environments. This begs the question of whether or not Africa experienced an increase in population pressure (perhaps due to development of more complex technology or behaviour) prior to the putative migrations into Europe in the Upper Paleolithic. This question cannot be answered with what fossil evidence is available.
The second point is a major question that will be dealt with in more detail in the section of this paper on morphology, but suffice it, for now, to ask, why is anything that looks marginally modern from the time period after the Neanderthal heyday automatically considered to be modern human? Why would Neanderthal morphology remain unchanged for ten to twenty thousand years of cohabitation with moderns while moderns underwent major changes in morphology when both underwent similar technological changes and environmental pressures? Hrdlicka’s third point poses the problem of if the moderns were superior technologically and behaviorally to the indigenous Neanderthals, why do they take over the same cave sites (and be replaced themselves by Neanderthals later in some cases!) inhabited by the inferior Neanderthals?
This point will be addressed in the section discussing technology and behaviour, as will Hrdlicka’s fourth point, which is more aptly described as a corollary to point three. His last point brings up the historical point of in modern migrations where populations were displaced (e.g. the Americas), the people did not go extinct, but rather, their way of life went extinct, and the indigenous populations contributed their genes to subsequent populations. Even in cases where white Europeans viewed the people as “animals”, interbreeding occurred at a significant level, and there is no reason to assume Upper Paleolithic hominids would be any different. This will be discussed in the section on genetic evidence.
The second major figure involved in supporting the continuity model with regards to the European Upper Paleolithic is Franz Weidenreich. Weidenreich was a student of Schwalbe’s and is best recognized with his work in pre-WWII China with the Zhoukoudien H. erectus material. Weidenreich was a proponent of the now-deceased concept of the single-species hypothesis. Until the 1970s, there was not enough material known to prove that more than one hominid lived at any one time on the planet, and the argument was that since culture was the major adaptive feature of hominids (especially tool use), any separate hominid species would be competing in the same adaptive niche, and one would eventually go extinct (Wolpoff 1999: 306-307).
This theory was destroyed by the irrefutable evidence of the robust australopithecines living at the same time as the gracile australopithecines. However, at the time, Weidenreich maintained that no more than one species of man existed at any one time during the Pleistocene (Weidenreich 1943b: 253). While he recognized that long-standing regional differences could lead to local differentiations, he believed interpopulation contacts would be sufficient to allow enough gene flow to prevent speciation.
While Weidenreich clearly expressed that regional populations would maintain gene flow (presumably in the same manner as hunter-gatherer groups in pre-contact North America and Africa) and common species status (Weidenreich 1947: 210), his views were misrepresented as direct regional continuity with no gene flow between the populations (Howells 1959: 236) and blasted as unreasonable to be expected to lead to the same species through regional evolution of hundreds of thousands of years.
Weidenreich clearly accepted a Neanderthal phase for modern human evolution in the same vein as Hrdlicka, which begs the question of why these two very prominent researchers that were posing similar criticisms of the replacement argument had a very little historical impact on the development of the replacement/continuity debate. This can be traced to the status each individual held. Weidenreich spent his later years (when he dealt specifically with fossil man and human evolution) working in the museum environment, and Hrdlicka spent his entire career in the Smithsonian. Neither had students and hence their views were not passed on to the next generation of practising paleoanthropologists, leading to the uncritical acceptance of the replacement model among paleoanthropologists of the subsequent generation.
After Weidenreich, basically, the only proponent of a Neanderthal stage of human evolution was Hans Weinert (Weinert 1944, 1947, 1951). Weinert received almost no interest in the English-speaking world for possibly several reasons: 1) his works were largely limited to German publication, limiting its availability, 2) his apparent obsession with the idea that the chimpanzee was a human ancestor (though his specific recognition that both humans and chimps have pursued their own unique evolutionary histories since the Tertiary belies this apparent obsession, and this idea may be due to mistranslations or misinterpretations of his work), and 3) Weinert was the sole perpetrator of German anthropology prior to WWI and through WWII, and the general collapse of a German academic field at this time may have been a factor in his anonymity(Brace 1964: 16).
Weinert gave three reasons for his acceptance of Neanderthals as a direct ancestor of modern humans:
Neanderthal characteristics are intermediate between Pithecanthropus (H. erectus) and modern man. All Middle Paleolithic hominids known at the time were Neanderthals and their ancestors, meaning there was not a candidate for a modern human ancestor other than the Neanderthals from the Middle Paleolithic. There is a high frequency of “Neanderthaloid” features in Upper Paleolithic humans relative to modern humans.
Weinert’s first point was an observation of his time, but though the Neanderthals do not make a good mediate between earlier hominids and modern humans, they do show a continuation of earlier traits, and some of their “unique” traits can be seen in modern humans, though it is unclear if this is support for some Neanderthal ancestry in modern man or just a happenstance of chance. Weinert’s second point is also now outdated, as several Middle Paleolithic specimens have been found in Africa and the Middle East, though from a historical perspective, it is curious to note the unwavering support seen for the replacement argument in the face of what was (at the time) very persuasive arguments for continuity.
Weinert’s final point is one of major concern and will be discussed in detail in the section on the fossil morphology. It is curious to note, that while the Neanderthals show a preponderance of traits that are not seen in modern humans, the Upper Paleolithic modern humans show these features at a very high frequency, which begs the question of where they came from if the modern African forms did not express these traits.
At this point, we come to the beginning of the modern synthesis of continuity theory. Beginning in the early 1960s (Brace 1962, 1964), C. Loring Brace began to take a look at the Neanderthal question and began to resurrect the arguments of Hrdlicka and Weidenreich, noting that Eastern European paleoanthropologists had been working under the assumption of Neanderthal continuity for years. This resurrection of the continuity argument gained support with the English publications of Jan Jelínek (1969), and the beginning of the professional career of Milford Wolpoff.
The debate thus began anew, with support for continuity gaining ground based especially on the morphology of Eastern and Central European Upper Paleolithic specimens and comparisons with modern Eastern European ethnic groups. In 1982, research into the evolution of mtDNA of human beings and its implications for the continuity/replacement debate swung the pendulum quickly back towards the replacement argument (Cann et al. 1982), with the public and scientific community becoming more and more accepting of a full replacement scenario, while a small group of paleoanthropologists including C.L. Brace, M.H. Wolpoff, and their students continue to make a claim for some level of continuity ranging from direct evolution of Neanderthals into modern humans (Brace 1995) to some level of interbreeding and genetic swamping of Neanderthal genes to produce the modern forms of humans with the retention of some Neanderthal features in certain regions (Smith 1985; Frayer 1992).
The early history of the debate over the placement of Neanderthals in modern human ancestry was discussed in more detail above than the more recent debates since the earliest arguments (as a whole) were based on bad dates, scrappy samples, and unfounded logic. The more modern discussion has at its disposal a far more complete picture of the fossil record and a far more accurate understanding of the functional significance of skeletal traits and the statistical methods by which to segregate samples of fossils into discrete categories. Unfortunately, this has not made the debate any clearer, as the participants in the debate over the fate of the Neanderthals are rarely unbiased in their examination of the facts (Graves 1991). In this brief paper, the amount of material and the depth in which it may be covered is limited, therefore, this discussion on the morphology of the fossil material will focus on the main points relevant to the debate of replacement versus continuity in Europe only.
In particular, the question that must be examined is whether or not there is evidence of continuity between the late Neanderthals and the early Upper Paleolithic humans. If there was a replacement of one population with another without any appreciable interbreeding occurring, then there should be a distinct morphological boundary between the Neanderthal and the modern specimens. Also, if all modern humans share a recent common ancestor, there should not be a marked divergence in the earliest extra-African H. sapiens populations (Wolpoff 1992: 35).
Day and Stringer provide an unambiguous morphological definition of modern humans based on six craniometric traits (1982: 832) including:
- A vault that is high but short, with a ratio of basion-bregma height to the maximum cranial length that exceeds 0.70
- A high frontal bone, as indicated by a frontal angle of less than 133°.
- Supraorbitals either absent or represented by a degenerated torus with a division into lateral and medial (i.e. superciliary arch) sections.
- A parietal with a long, high arch that has a parietal angle of less than 138°.
- A parietal shape that is superiorly broad and inferiorly narrow as reflected by a ration of the bregma-asterion chord to the biasterionic breadth that exceeds 1.19.
- A well-curved occipital bone, as indicated by an occipital angle of greater than 114°.
Day and Stringer then go on to explain that any modern human should express 50% of these characteristics of the measures that may be taken. The problem is, this definition excludes many living human groups from the status of a “modern human”, and as shown by Wolpoff (1992: 36) when one looks at Australian Aborigine samples. Looking at more ancient Australian samples that are definitely modern (such as the Kow Swamp and Coobool material), similar results are indicated, with a large percentage (~30%) segregated as not belonging to the modern human species (Wolpoff 1992: 37-39).
Thus, this definition of modern human craniometrics is not valid for examining the Neanderthal replacement/continuity debate if it cannot even distinguish undeniably modern humans on a reliable basis. The morphological distinction of modern H. sapiens from earlier archaic forms is elusive, and due to the variable nature of human skeletal and cranial morphology, possibly a statistically unanswerable question. Thus – setting aside for the moment the problem of actually defining what it means to be modern human – the question of continuity versus replacement falls back to the question of transitional forms.
Specimens that are transitional between modern H. sapiens and ancestral populations should reflect the geographic source for the species, especially if the ancestral populations are restricted to a single region. This is clearly the proposition stated in the replacement modern, with Sub-Saharan Africa the place of origin for the development of modern human forms. The replacement hypothesis expects that modern human forms, wherever they are found, should exhibit the regional features characteristic of their ancestral Sub-Saharan African populations, whereas the continuity model expects regional populations to exhibit features characteristic of the populations ancestral to them and spatially located in the same geographic area.
Thus, both theories predict the presence of transitional forms in Africa, and the presence of these transitional African forms are readily agreed upon by basically all researchers (Stringer & Andrews 1988; Wolpoff 1999; Smith 1992; Frayer 1992; Stringer & Gamble 1993; Bräuer 1984; Trinkaus 1986). However, when it comes to Europe and Asia, proponents of replacement often claim that there is no evidence of transitional specimens in the fossil record. For example, Stringer and Andrews (1988: 1266) claim that “although Europe and southwest Asia have the most complete fossil record for this period, there is an absence of Neanderthal-modern Homo sapiens transitional fossils in either area.” In fact, however, there have been numerous researchers that have found evidence of continuity from the Neanderthals to modern humans, and have explained it by either claiming in situ evolution or some sort of hybridization (Hrdlicka 1927, 1930; Weidenreich 1943a; Brace 1964; Brose & Wolpoff 1971; Jelínek 1969; Smith 1982; Frayer 1986; Trinkaus & Smith 1985; Radovcic 1985).
Even if one ignores the fact that the same features used to characterize the African transitional fossils are, according to Stringer & Andrews (1988), unsuitable for comparative analysis, and agrees that features such as browridge development, tooth size patterning, and protruding occipitals are not useful as a regional feature to look at for continuity from Neanderthals to Upper Paleolithic modern humans because they are homoplasies (however, see Smith 1992), there are characteristics that are considered a part of the Neanderthal suite that shows continuity from Neanderthals through the subsequent modern human’s populations. For example, three Neanderthal traits that show continuity specifically from Neanderthals to Upper Paleolithic humans to modern day humans include the presence of a supra-iniac fossa, the shape of the mandibular foramen, and the features of the axillary scapular border (Frayer 1992: 180-185).
For example, when one looks at the presence of supra-iniac fossae:
- Present Absent (n)
- Neanderthals 100 0 24
- Early Upper Paleolithic 25 75 20
- Late Upper Paleolithic 23.7 76.3 38
- Mesolithic 19.3 80.7 161
- Medieval Hungarians 5.9 94.1 237
- Modern French 9 98 100
- Table 1 (Frayer 1992: 182)
One sees that the presence of this trait – considered a probably Neanderthal autapomorphy by Stringer (1984: 55) – is highest in the earliest human populations, and reduces over time until it is nearly non-existent in modern populations.
Similarly, when one looks at the frequency of horizontal-oval (H-O) mandibular foramen in these populations:
- H-O Normal (n)
- Neanderthals 52.6 47.4 19
- Early Upper Paleolithic 44.4 55.6 9
- Late Upper Paleolithic 5.3 94.7 38
- Mesolithic 1.9 98.1 161
- Medieval Hungarians 1.4 98.6 208
- Table 2 (Frayer 1992: 183)
One sees the same pattern of reduction of this orientation through time, with a very similar frequency between the Neanderthals and the early Upper Paleolithic humans. Stringer (1984: 55) also lists this trait as a probably Neanderthal autapomorphy, which – if true – clearly shows some conservation of this regional feature in populations subsequent to the Neanderthals. Finally, the scapular morphology of the axillary border (attachment of M. teres minor) is typically considered to follow a dorsal pattern in Neanderthals and a ventral pattern in modern humans. However, when one examines the prevalence of dorsal, ventral, and bisulcate patterns, one finds this distribution:
Scapular Morphology Chart
Which shows a shift from the more archaic (Neanderthal-like) dorsal pattern to an intermediate bisulcate pattern to the modern ventral form (Frayer 1992: 184). These features do not show a marked shift from the Neanderthal pattern to a modern human pattern with the Upper Paleolithic human populations, but rather an evolutionary trend in these features that indicates some continuity in regional traits and hence does not support total replacement.
The topic of behaviour is one that could be expanded on and discussed in extreme detail, but in order to keep this paper focused, this section will deal only with the technological transition from the Middle to the Upper Paleolithic. The section will begin with a short description of the relevant sites and dates, follow with a short discussion of the distinguishing characteristics of the various industries relevant to this time period, and end with a discussion of what the Neanderthals are responsible for, and what the Upper Paleolithic modern humans were responsible for.
The site of Saint Césaire has been dated to approximately 36 kyr and includes the Upper Paleolithic tradition of the Châtelperronian with an associated Neanderthal specimen, and thus directly provides evidence that Neanderthals were the makers of the Châtelperronian, vindicating the 1972 proposal of Bordes. Arcy-Sur-Cure is another French Châtelperronian site dated to approximately 34 kyr, and though its association with Neanderthals is based on isolated teeth, there is general agreement that it is a Neanderthal site (Wolpoff 1999: Stringer & Gamble 1993). Bacho Kiro is sometimes referred to as a “Pre-Aurignacian” site, but its technological affiliations are as unclear as its association with either modern humans or Neanderthals.
It is dated to greater than 43 kyr, and cannot be clearly associated with either moderns or Neanderthals, and the most that can be said for the technology is that it is Upper Paleolithic. El Castillo is an Aurignacian site that has been dated to approximately 37 kyr and has associated undiagnostic cranial fragments. As with Bacho Kiro, replacement advocates claim the site as an early modern site, and continuity advocates claim it as a Neanderthal site, and neither claim can be substantiated by fossil evidence. The Vindija site in Croatia is a very important site with occupations ranging from the Middle Paleolithic through the Upper Paleolithic until 28 kyr ago, with associations with Aurignacian material and Neanderthal remains. The l’Arbreda site in Spain is dated to 38 kyr ago and is associated with the Aurignacian but not with diagnostic hominid remains. Other important sites include Roc de Combe, El Perado, and Le Piage due to the alternating layers of Aurignacian and Châtelperronian artefacts.
What this temporal and spatial distribution of sites means is completely unclear, and is not helped by the fact that an individual that supports replacement will take any evidence of the Aurignacian as evidence of early modern residence even though there is no evidence indicating this link in the vast majority of sites. What is clear, is that there is an East to West development of the Aurignacian from either migrations of modern humans or the in situ development of the industries or spread of the technology sans the spread of biology (Stringer & Gamble 1993; Wolpoff 1999; Clark 1992).
The make-up of these industries is similar but perceivably different. The Châtelperronian was definitely a local development, with its roots in European Mousterian lithic traditions, and is characterized by backed bladelets reminiscent of Mousterian knives, endscrapers, engraving tools (e.g. burins), personal adornment in the form of pierced bone and teeth necklaces, some use of bone and ivory, but relatively little compared to the later Aurignacian. In general, it was a refined Mousterian technology that made use of prismatic methods rather than the Levallois technique, and with increased the range of its tool kit and started to make use of materials other than stone.
The Aurignacian was similar in many ways to the Châtelperronian, but it made much greater use of bone and antler materials to make tools, there was the development of barbed spear points and direct evidence of hafted tools, and a much greater development of symbolic art in the form of personal adornment. It is possible that the Châtelperronian developed through the acculturation of Neanderthals by modern human Aurignacian culture, and it is also possible that some or all of the Aurignacian variants developed from the Châtelperronian and its variants (e.g. Szeletian, Uluzzian).
The Châtelperronian has some definite ties to Neanderthals based on associated remains like Saint-Césare, and through the analysis of the Châtelperronian as an extension/development of the European Mousterian. The Aurignacian, on the other hand, is generally assumed to be an early modern technology, but by the time there are early moderns that can be associated with the Aurignacian, there are already Neanderthals associated with it as well, making the determination of who made what debatable (Wolpoff 1999; Clark 1992; Brace 1964; Stringer & Andrews 1988).
The problem with this question of who is responsible for the Aurignacian is that there is no answer at this point. There is a wealth of sites where typologies have been applied to give either “Aurignacian” or “Châtelperronian” status to the sites, and beyond the issue that these categories are not qualitatively distinct in many cases, there is not enough associated fossil material to really say what population was doing what. Until there are more associated remains found at sites that can be fully documented or a really early but distinct Aurignacian industry is found either in Africa or Europe when there will be little argument over which population gets the credit, the debate over this issue is moot. What is important to note about this problem, is that contrary to the statements of certainty espoused by some strict replacement advocates (Stringer & Gamble 1993), there is really no way to objectively come to a conclusion about replacement or continuity based on the technology.
The genetic evidence for and against the theories of replacement and continuity are very interesting in that they have become the primary focus of much current debate about the fate of the Neanderthals, and in that the conclusions that have been reached by molecular biologists are so readily accepted by the scientist and the layperson alike. The beginning of the genetic revolution of the replacement/continuity debate began with the groundbreaking work of Cann and Stoneking in the 1980s (Cann 1988; Cann et al. 1987; Stoneking & Cann 1989) that was used as evidence that all modern human populations had a recent common ancestor between 140 kyr ago and 280 kyr ago.
This work was based on examinations of the variation within mitochondrial DNA sequences in modern humans, and used several assumptions on which to determine a coalescence point for modern human mtDNA:
- Mitochondrial DNA is conserved from generation to generation without any recombination.
- Mitochondrial DNA is passed on from mother to child without any paternal inheritance of mitochondria.
- Since there is no natural selection on mtDNA mutations will accumulate rapidly and at a relatively stable rate over long periods of time.
When human mtDNA was examined several things were evident and purported as evidence supporting the “Mitochondrial Eve” model of replacement, including the presence of the greatest variation in African populations, very little variation between geographic origins, and a recent coalescence date of around 200 kyr. Basically, the mtDNA evidence informed the researchers that modern humans had undergone a major population bottleneck that reduced the variation within the species to a very low level, and then the population expanded as fully modern humans throughout the world displacing indigenous populations.
The problem is, the assumptions behind the mtEve calculations are not necessarily true. First, mitochondrial DNA might recombine (Awadalla et al. 1999), meaning that any coalescence date calculated from the assumption of strict clonal transfer of mtDNA from mother to offspring is going to be inaccurate. Second, mitochondrial DNA may not always be inherited strictly from the mother only, and in fact, the concept that mtDNA is solely inherited maternally was based – not on observation – but on an incorrect cytological description from 1935 (Wells et al. 1935: 149) that became folk science knowledge and eventually was even treated as fact in textbooks (Ankel-Simons & Cummins 1996).
While there is some evidence that paternally inherited mtDNA is destroyed through various antigen processes soon after fertilization, there is also evidence that for every 10,000 maternal mitochondria are passed on, one paternal mitochondrion is passed on and survives (Gyllensten et al. 1991), meaning that any coalescence date would have to take into account the geometric effect this small amount of paternal mitochondria could make through multiple generations (in the same manner that a small interest rate can make a large difference in an eventual total versus simply the addition of principle). Finally, there is not a neutral accumulation of variation in mtDNA that can be accurately measured by one of the many “molecular clocks” used in these coalescence calculations.
These clocks are calibrated by either 1) arbitrary use of a divergence date for humans and a different primate (usually orangutans), which means that the clock rate is based on the circular logic of divergence dates estimated by other molecular means 2) the use of direct observations of mutation rates in lab animals, which then has to deal with the problem that somatic and mtDNA mutations rates are highly correlated with body size and metabolism, as well as generation length, so any clock calibrated by using mouse mutation rates is going to be too fast (Wu & Li 1985). This indicates that the coalescence date for all modern humans (and the Neanderthal DNA issues discussed below) needs to be reconsidered.
However, beyond the technical problems with the genetic methods, there is a difference in theoretical orientation that allows both sides of the debate to use the variation in modern populations as evidence that supports their theory. Most supporters of continuity have taken up the cry of, “Follow the fossils!”, as they seem to be far more supportive of continuity than the genetic data. However, Wolpoff (1992; 1999) maintains that the reduced variation in human mtDNA is not indicative of a recent common ancestor of modern humans, but rather of a genetic bottleneck in the mtDNA only, with no necessary link to population bottlenecks.
This idea is supported to some extent by the greater nuclear DNA variation seen in modern humans relative to the mtDNA, which gives a coalescence date of 1.29 myr for the common ancestor of modern humans, which is much more in sync with the fossil record that the recent common ancestor date (Zhao et al. 2000). If there was a population bottleneck that reduced the genetic variation in human mtDNA sequences, then there should be a correlated reduction in nuclear DNA variation, which there is not.
This may mean that while populations did not undergo a bottleneck, there may have been a selective bottleneck in the mtDNA, whereby some selective value (or random chance), variation within the mtDNA was lost. This idea may or may not be correct or well-supported by the data, but it does resolve itself to the issue of the extensive geographic range of Homo, which would likely be due to population pressure, and the unlikely possibility that a population bottleneck could so severely affect the populations of humans, that a separate species would arise and spread quickly across the Old World displacing resident populations.
The replacement/continuity debate took another turn towards the general acceptance of the replacement hypothesis with the extraction of mtDNA from Neanderthal fossil specimens. To date, three Neanderthal mtDNA fragments have been reconstructed and analyzed (Krings et al. 1997; Ovchinnikov et al. 2000; Krings et al. 2000). The method of mtDNA extraction has bee similar for each, where a quantity of mtDNA fragments were recovered from the specimens, the fragments were separated based on what the researchers believed was contamination, the amplification of these fragments, the reconstruction of fragments into a larger region of mtDNA using overlapping regions, and the comparison to the reconstructed fragment to modern human mtDNA.
All three studies have come to the same general conclusion, that modern humans and Neanderthals share a common ancestor somewhere from 450 kyr ago to 850 kyr ago. Unfortunately, there are several major flaws with these studies. First, the researchers make assumptions that Neanderthal and modern human mtDNA should look different, so to control for contamination, and fragments that “look” like modern human mtDNA is removed as contamination, meaning the researchers’ a priori assumptions are guaranteeing that the reconstructed mtDNA will be significantly different from a modern human. Also, the reduction in mtDNA variation in modern humans is not in question, but there is really no way of knowing when that genetic bottleneck occurred, and so the greater variation seen in the Neanderthal mtDNA sequences may simply be an artefact of a more diverse mitochondrial genome that hasn’t yet gone through a selection event.
Since there really is not a neutral accumulation of mutations (and hence variation) in mtDNA, due to the simultaneous random loss of variation at the same time mutations are increasing the variation, it is an invalid assumption to simply go backwards from modern variation through assumed mutation rates to get to a coalescence point since there could have been any number of bottlenecks and expansions at various times in human history. This means that any date of coalescence of humans with Neanderthals will always give a date based on the assumptions behind the model. In addition, if there was very extreme isolation with very minimal gene flow, speciation would not necessarily have occurred (Templeton 1996), and using Neanderthals dating prior to the migrations of modern humans into Europe means that hybridization models cannot be accurately tested. Until an accepted early modern human from the Upper Paleolithic is similarly tested, any conclusions drawn cannot be accurate, since one cannot date coalescence based on one lineage.
In recent years, the Out of Africa II model of strict replacement has become preeminent in anthropology and the press as the answer to the puzzle of modern human origins. However, I have attempted to show the historical basis for the two opposing views of replacement and continuity, and show what information is actually being used to support both sides of the debate (especially the replacement model as it is currently the best-accepted explanation and hence the one most in need of critique), in order to show that the debate is not so clear cut and that there is quite good evidence for some sort of continuity in Europe. The fossil evidence clearly shows that there is not a sudden shift from one morphological type to another, but rather a reduction in features as part of an evolutionary trend that may be linked to changes in culture (e.g. greater use of cooking, better hunting methods) that led to changes in selective pressures.
The behavioral evidence discussed briefly in this paper pointed out that the evidence does not evince any particular conclusion, and whether or not a strict replacement model, a strict continuity model, or a middle-of-the-road hybridization model is believed, the behavioral data in terms of the archaeology does not differentiate populations any clearer than the fossil morphology does. Until better evidence is discovered, it is likely that this will remain the case, with both sides talking past the other with statements of their superior interpretation of the technological record.
The genetics issue is one of statistical manipulation. Different assumptions are inherent in every interpretation of the data and even in the way the data is extracted, meaning that the preconceived opinions that are necessary to determine what assumption one will use biases the results to support the assumptions inherent in the model. The extraction of Neanderthal mtDNA is more helpful, but until it is put into the proper perspective by the examination of several early modern specimens, it simply increases speculation, without providing solid evidence.
When all is said and done, I truly believe that the evidence supports some degree of regional continuity in Europe, since most cranial traits show continuous trends from Neanderthal to Early Upper Paleolithic humans, to Late Upper Paleolithic humans, to modern humans, and there is not a sudden shift in morphology. However, the evidence does not seem to support a strict in situ continuity model (Brace 1995), since there seems clear evidence that humans with warm adapted limb proportions (Holliday 1997; Holliday 1999) were either migrating into Europe or spreading their genes into Europe.
It seems likely that the relatively rapid morphological changes occurred through the combination of the evolutionary pressures that maintained hyper-robust forms being relaxed due to technological (cultural changes) and the introduction of an influx of more gracile and warm adapted genes from African populations. Thus, it seems that a restricted hybridization model is the best-supported theory in terms of the evidence that can be taken at absolute face value, while the strict replacement and continuity models do not hold up.