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Neandertals were a morphologically distinct human population that existed in Europe and Western Asia from about 200,000 to 30,000 BP (before present). The first recognized Neandertal discovery occurred in 1856, when the remains of part of the skeleton of one individual was discovered in the Feldhofer grotto, in Neander Valley, near Düsseldorf, Germany. This material was recovered by quarry workers and set aside for a local teacher and amateur naturalist, Johann Karl Fuhlrott. Fuhlrott suspected that the find might be important and took the material to anatomist Hermann Schaaffhausen. The material was jointly announced in 1857, two years before Darwin published The Origin of Species. The term Neandertal is derived from the species designation Homo Neandertalensis, given to the material by William King in an 1863 meeting of the British Association. Feldhoffer was the first recognized Neandertal discovery, but in later years, other earlier finds were placed within the Neandertal clade, including the Engis child discovered in Belgium in 1829, and the Forbes Quarry material discovered in Gibraltar in 1848.
Early interpretations of Neandertals were marred by misrepresentation and misdiagnoses of the nature of the anatomical features seen in the material. In the early years after the Feldhofer discovery, many researchers did not even recognize the antiquity of the material. For example, in 1872, Rudolf Virchow published a report claiming that the Feldhofer individual was simply an early 19th century Mongolian Cossack afflicted by rickets, a view originally proposed by Geheime-Rath Mayer soon after the material was announced. Once the antiquity of the Neandertals was established, researchers began to develop hypotheses regarding who the Neandertals were and what relationship they had to modern human beings.
While many proponents of Darwin’s theory of descent with modification were willing or even eager to accept the Neandertal material as evidence of an intermediate in our evolution, the prevailing view quickly became that Neandertals were much too primitive in form to be directly related to modern human beings. This development could be considered an unhappy circumstance, as the more spectacular Neandertal discoveries in France overshadowed the description of the large, fragmentary Krapina sample from Croatia. Furthermore, several important French finds at this time, such as Le Moustier and La Chapelle-aux-Saints in 1908, La Ferassie in 1909, and La Quina in 1911, were published in a sequence that became quite detrimental to the interpretation of Neandertals for years to come. The description of Le Moustier was delayed and incorrectly reconstructed, while La Ferassie was trusted to Marcellin Boule, who was preoccupied with the description of La Chapelle. When Boule published his description of La Chapelle, it overshadowed the La Quina find and quickly became the penultimate description of Neandertal morphology. Unfortunately, La Chapelle was an elderly individual suffering from a variety of ailments, and Boule interpreted the material to mean that Neandertals were bent-knee walking brutes with little intelligence, much closer to apes than modern humans. This view of Neandertals dominated in academic circles until after World War II.
Boule had created the typological characterization of Neandertals based on one of the most atypical Neandertal specimens known: an older individual afflicted by a suite of pathological conditions. While the French Neandertal material created the dominant image of Neandertals, the Krapina assemblage was also available to these early researchers, an assemblage that not only clearly indicated that the anatomy of La Chapelle was not typical of Neandertals, but one that gave a sense of the wide range of variation seen within this population. The lack of the recognition of this variation underlay much of the early work that unequivocally dismissed Neandertals from the ancestry of modern humans.
Morphology of the Neandertals
The question of what makes an individual a Neandertal is a difficult one to answer because, while many autopomorphies or unique derived characters have been proposed for the Neandertals over the years, none are true autopomorphies. Some proposed features are characteristic of Neandertals from only particular geographic regions, many are found in some modern human populations in varying frequencies, and others are known to be present in more archaic populations and represent primitive characteristics. Regardless of the degree of contribution to the modern human genome, the Neandertal morphotype is essentially a matter of character frequency rather than a matter of unique derived characters. While the Neandertals apparently lack true autopomorphies to distinguish them from modern humans, the suite of character traits found in Neandertals do distinguish them as a distinct group, either as a racial variant or as a closely related sister clade to modern humans.
The typological perspective common in treatments of the differences between Neandertals and modern humans is unfortunate in that it impedes an appreciation for normal variation seen in individuals within a population. As noted, there are no true autopomorphies in Neandertals that unequivocally exclude them from having had gene flow with contemporary populations in other parts of the world or from contributing to the Upper Paleolithic populations that follow them. This creates a quandary when we compose a list of morphological characteristics that distinguish Neandertals, as there are not many features that we can use to distinguish them from their ancestors, from contemporary populations, and from modern humans at the same time. Instead, we make a more useful distinction when we compare Neandertals to these other populations individually and describe how they differ from each group as opposed to the characters that distinguish them as a group.
Although we cannot overstate the importance of viewing characteristics of Neandertal morphology from the perspective of evolutionary trends rather than simple typology, a number of general morphological features characterize Neandertals inclusively. Lambdoidal flattening at the rear of the parietals and top of the occipital creates a short vertical face to the occipital, forming the characteristic “bunning” seen in Neandertal crania. This feature results in the elongation of the cranium, so that the central limit of the nuchal muscles is delineated by small pits on the occipital called suprainiac fossae, rather than the external occipital protuberance on the vertical surface, as seen in modern humans. The suprainiac fossae are generally superior to another Neandertal characteristic, the occipital torus, which is a bony ridge that runs horizontally along the occipital. Another consequence of the cranial elongation seen in Neandertals is the position of the foramen magnum more anterior relative to the position of the external auditory meati. In earlier pre-Neandertals as well as in modern humans, when a line is drawn between the external auditory meati, the foramen magnum is positioned posterior to the line, but in Neandertals the foramen magnum is positioned much more anteriorly, so that the line passes behind the foramen magnum. This positioning improves the leverage of the sternocleidomastoid muscles, which act to turn the head and stabilize the head during anterior teeth use. The improved leverage in Neandertals results in a reduction of the strength of the muscles needed to perform these actions, and, therefore, a reduced attachment area represented by a reduced mastoid process. While the mastoid process is reduced in size in Neandertals, the juxtamastoid process just medial to the mastoid process is well developed, often larger than the mastoid process. This area marks the attachment site for the digastric muscle, which retracts the mandible, suggesting an adaptation to anterior tooth loading. These changes to the temporal region may be partially responsible for the inner ear morphology seen in Neandertals that Fred Spoor claims as a potential autopomorphy in Neandertals.
Neandertals are also characterized by a well-developed supraorbital torus. This bar of bone across the top of the eye sockets is much reduced relative to earlier pre-Neandertals and is formed by two arches that follow the contour of the orbitals with a supratoral sulcus separating them. The reduction relative to earlier forms is a consequence of absolute reduction in robusticity, as well as the frontal rising more anteriorly. In Neandertals the supraorbital torus is characterized by the expansion of the frontal sinuses. The maxillary sinuses are also expanded in Neandertals, creating a puffy midface appearance on either side of the nasal aperture, such that most Neandertals lack a canine fossa. The zygomatics are swept backwards, facing much more laterally than seen in non- Neandertal populations. Another prominent feature of Neandertals is their large nose. Neandertal noses are characterized as both very wide and very tall, with the wide nasal breadth apparently a feature inherited from their ancestors and the increased nasal height a Neandertal character. Considered together, these features combine to give Neandertals the appearance of well-developed mid-face prognathism.
The mandible form also shows a number of features we use to characterize Neandertal morphology. Most individuals have a retreating mandibular symphysis, thereby lacking a mental eminence or chin. The lack of a chin is widely used as a peculiar Neandertal trait, but many later Neandertals have some degree of development of this feature, and many archaic Homo sapiens lack a well-developed mental eminence.Many Neandertal mandibles have a retromolar space, which is a space on the horizontal ramus of the mandible between the distal surface of the third molar and the anterior border of the ascending ramus. The horizontal-oval morphology of the mandibular foramen on the internal surface of the ascending ramus is another trait characteristic of Neandertal mandibles. This morphology is created by the strong development of the sphenomandibular ligament insertion site, thus, probably related to the strong masticatory musculature of the Neandertals.
Neandertals have relatively reduced postcanine dentition compared to their antecedents, but their size is larger than that seen in most modern human populations. The anterior dentition of Neandertals, however, is enlarged over any earlier, contemporary, or later humans. Characteristic wear patterns seen in many Neandertal individuals indicate that they probably used their anterior teeth as tools, likely for use as vices to clamp down on material that was being worked.
Neandertal brains have always been characterized as being absolutely large, with many researchers emphasizing that Neandertals had bigger brains than modern humans. This is not quite correct and is an interpretation that was influenced by several biasing effects. There are many more male than female crania among the known Neandertal specimens for which a cranial capacity may be confidently determined. With a degree of sexual dimorphism grossly similar to modern humans, this means that the mean cranial capacity is skewed toward the larger male size. For example, the middle sex mean for Würm Neandertals is approximately 1430 cc, a figure that compares favorably with many modern populations. In fact, when compared against body size, Neandertals are slightly less encephalized than modern humans. Neandertals had appreciably larger brains than their Middle Pleistocene ancestors, however.
In general, the postcranial morphology of Neandertals is little differentiated from that of modern humans. Almost all characteristics of the Neandertal skeleton fall within the modern human range, often most similar to modern cold-adapted populations such as Eskimo groups. Some of the features peculiar to Neandertals includes the morphology of the axillary border of the scapula and the shape of the pelvis. In modern humans, the axillary border of the scapula has a ventral thickening for the insertion of the teres minor muscles, while the majority of Neandertals have dorsal thickening indicating that the muscles insert on the back of the scapula along its lateral border. This feature has at times been argued as a Neandertal autopomorphy, but is actually present in early European modern humans and decreases in frequency in favor of first a bisulcate (dorsal and ventral thickening), then ventral pattern. There are also known examples of the dorsal morphology in modern humans of particular occupations and is quite likely more a reflection of behavior than ancestry.
The shape of the Neandertal pelvis differs slightly from that of modern humans. Unfortunately, the known Neandertal specimens are male, making it difficult to make statements relating the shape of the pelvis to birthing differences between Neandertals and modern humans. In Neandertals, the superior pubic ramus is long, thin, and relatively flattened. This morphology primarily acts to widen the pelvis at the front, rotating the blades of the pelvis outward along the hip joint. This difference causes very little difference in the depth of the birth canal, front to back, and therefore likely has little to do with adaptations to birthing larger headed offspring. Yoel Rak conducted a detailed analysis of the complete Kebara pelvis and argued that the differences in the shape of the pelvis relative to the position of the femur indicate stronger abduction movements in Neandertals relative to modern humans. The significance of the morphology of the Neandertal pelvis is still subject to quite a wide range of ideas and very little agreement. Most researchers agree, however, that there was likely very little substantive differences in Neandertal gait and that such relatively minor differences may very well be the result of behavioral locomotive patterns than genetic differences.
The relative limb lengths of Neandertals reflect cold-adaptation as predicted from Bergman’s and Allen’s rules. Compared to body length, Neandertals tend to have relatively shorter arms and legs and distal limbs that are short in proportion relative to proximal limbs. Scientists generally accept that these characteristics are a consequence of cold-adaptation and are similar although more developed to those seen in modern human cold-adapted populations. Neandertals also tend to have much deeper and wider chests than most modern human populations, reflected by the radius of curvature of their ribs and clavicles that are long relative to their stature. These features of thicker trunk size and shorter limbs are characteristic of the cold-adapted European Neandertals and do not particularly apply to the West Asian Neandertals. This indicates that these are yet more Neandertal characteristics that result from adaptation to their environment rather than real species differences between them and modern humans.
The shape of the Neandertal trunk and limbs may explain some researchers’ claims that Neandertals were quite short, but, in reality, Neandertals show very little difference in height with modern humans. Neandertal males average 165 cm and females average 156 cm, slightly shorter (approximately one to two inches) than the European average but taller than many other modern human populations. Neandertal stature is approximately equivalent to pre-World War I French. Neandertals are not particularly short at all, simply heavily built with relatively shorter limbs reflecting cold adaptation.
Behavior of the Neandertals
Far more vigorously than differences in morphology, scientists and researchers continue to debate the cultural differences between Neandertals and early Upper Paleolithic modern humans. Evidence of behavior from the archaeological record is subject to a variety of interpretations that often reflect the bias of the researcher. Researchers who see Neandertals as significantly different from and perhaps inferior to early modern humans will invariably interpret sites and data conservatively with regard to behavioral complexity. In the same vein, researchers who view Neandertals as ancestral to later European populations consistently interpret sites and data as showing high degrees of mental and social complexity. As in all such polarized intellectual debates, there resides a middle ground.
While scientists continue to debate the degree of complexity shown by Neandertals, evidence points to a definite increase in complex behavior from the beginning to the end of the Middle Paleolithic. For example, most known Neandertal burials come from the later Middle Paleolithic, with many of them representing the classic Neandertals of France (70,000–35,000 BP). Although a few researchers question whether these burials are deliberate, the majority of researchers accept that burial was a common occurrence that became more common as Neandertals evolved over time.
We can relate behavioral complexity with other strong pieces of evidence, including
- the creation of structures at sites such as Lazaret (presumably for shelter)
- the presence of worn blocks of pigments such as red and yellow ochre or black manganese remnants in various cave sites (potentially for body adornment or for processing hides)
- pierced teeth and other beads and pendants from some later Neandertal sites (evidence for body adornment or totems)
- the flute found in Divje Babe Cave
Evidence of Neandertals’ care of the sick, injured, or elderly comes from several sites where individuals show healing of cranial fractures whose seriousness likely meant the individuals were incapacitated for a period of time and, most convincingly in one male from Shanidar, who survived to maturity despite several crippling injuries that left one arm useless and also may have left him blind. While the significance of these pieces of evidence is arguable and a few researchers have vehemently challenged the validity of some of these examples, they are well-supported interpretations. As with some other anthropological sleuthing, however, the frequency of potential clues is very low, bringing up the question of whether the presence of isolated pieces of evidence for symbolic or complex behavior is enough evidence to support the contention that such behaviors were widespread, as they clearly were among later Upper Paleolithic people in Europe.
Researchers who question the strength of the evidence for such behaviors have good reason to be dubious. We know that a number of interpretations of Neandertal behavior were incorrect. For example, researchers have strongly criticized the widely reported Shanidar burial with flowers, the Teshik-Tash burial surrounded by goat horns, and the Neandertal bear cult. The presence of grave goods in many of the reported Neandertal burials is also suspect, considering that the so-called artifacts are no different than the debris found in surrounding sediments. While the presence of grave goods is unlikely, other mortuary practices may be indicated by the evidence for secondary burial and defleshing at Krapina, Kebara, and on several of the Neandertal infants.
One of the most important aspects of behavior for paleoanthropologists is subsistence behavior, in particular, meat-eating behaviors. These behaviors are important because they often leave direct evidence on fauna recovered from archaeological settings. This may be particularly important for Neandertals, as isotopic analysis of Neandertal remains indicate a very high level of animal protein, similar to that seen in high latitude indigenous Eskimo populations. The interpretation of Neandertal subsistence patterns has led to very disparate proposed behavioral and cultural suites. Work by Mary Stiner on Italian cave sites indicated a shift in subsistence patterns from nonconfrontational scavenging prior to 55,000 BP supported by a head-dominated assemblage, to hunting behaviors after 55,000 BP supported by the presence of more complete carcasses of prime age. This work led to a flurry of speculation by researchers that earlier Neandertals were highly mobile foragers with wider geographic ranges and focused on opportunistic scavenging as well as exploitation of primarily high value foods. This argument was used to support a lack of fore-planning by Neandertals, essentially intimating roving bands of dim hominids eating whatever was available and moving on when food ran out. Only near the end of their existence did Neandertals focus on more residential behavior with less expedient tool use, wider exploitation of food resources, and active hunting of particular game. However, the assemblages on which these analyses were conducted were earlier in the century. Curtis Marean made a convincing argument that changing excavation techniques artificially created the differences between the two time periods, and he followed the argument with analyses of other Middle Paleolithic sites that have been excavated with different procedures that showed no evidence of scavenging as a major subsistence pattern in Neandertals. This interpretation is convincing, considering the presence of spears as early as 450,000 BP at Schöningen, and many sites throughout the Middle Paleolithic show a single-species-dominated faunal assemblage indicative of selective hunting. In fact, Marean has found no meaningful difference in subsistence patterns between Middle and early Upper Paleolithic sites based on faunal collections. From the perspective of hunting behavior and carcass processing, the shift in tool technology does not necessarily mean a shift in subsistence behavior.
Other direct pieces of evidence for behavior in the Neandertals are the tools that they created and used. The designation of the Paleolithic stages is based upon technological types, and, therefore, the transition from the Lower to the Middle and the Middle to the Upper Paleolithic took place at different times in different places. The pre-Neandertals used the Acheulean industry that is associated with bifaces, stones flaked on both sides to create the cutting edge. The typical Acheulean form is that of the teardrop-shaped hand axe. As the Neandertals emerged approximately 250,000–200,000 years ago, there was a shift from the typical Acheulean industries to the Middle Paleolithic Mousterian industries. Mousterian industries are the principal technology associated with Neandertals. This industry appeared in various forms, including a Mousterian of Acheulean tradition that includes a large component of hand axes, as well as more complex forms with a high frequency of burins, side scrapers, points, and denticulates. Many of the Mousterian assemblages are associated with the Levallois technique of flake removal around a core, followed by blade removal from the center of the core across the dome created by peripheral flake removal. The Upper Paleolithic is associated with high frequencies of blades (flakes more than twice as long as wide) and common use of bone and antler rather than stone. The Middle to Upper Paleolithic transition was more of a transition in frequency of tool usage rather than the invention of new tool types, as Upper Paleolithic type tools have been found at varying frequencies from the Lower Paleolithic upward. While the differences may be more quantitative rather than the qualitative that is often described, there are particular identifiable features in Upper Paleolithic industries. There are two Upper Paleolithic traditions of primary importance in the discussion of Neandertals: the Châtelperronian and the Aurignacian. The Châtelperronian is definitively a Neandertal technology, while the origins of the Aurignacian are less clear. The Châtelperronian is characterized by backed bladelets, and while the Aurignacian was similar in many ways to the Châtelperronian, it was characterized by much more use of bone and antler in tool production, the creation of split backed bladelets, and barbed spear points with more developed hafting.
Many researchers have argued for a cultural revolution in the shift from the Middle to Upper Paleolithic, but the actual shift was more of a gradual change that occurred at various times across the European landscape. It may very well indicate more complex behavior, but, although the tools are seemingly more sophisticated, they are actually no more difficult to manufacture than Mousterian tools and do not seem to perform functions distinctly different than that of earlier assemblages. There are differences, and some hypotheses have been proposed to explain differential behavior, such as Olga Soffer’s proposition that the need for more microblades was to thinly fillet meat for drying, allowing food storage. These behaviors do definitively occur later in the Upper Paleolithic, but during the important period of transition and the disappearance of the Neandertals, there is little unequivocal evidence for these behaviors. The bulk of the information available on Neandertal culture does not lead to an unequivocal conclusion regarding Neandertal behavior and affinity, or lack thereof, with early modern humans.
Replacement of Continuity?
Two polarized positions—the replacement model and the continuity model—characterize the argument over the fate of the Neandertals. The extreme manifestations of these positions is that Neandertals were either summarily replaced by invading anatomically modern humans or that they evolved in situ into modern Europeans. As we have gained a better understanding of population genetics and speciation over the past several decades, scientists have abandoned completely the extreme continuity position, but with the development of mitochondrial DNA (mtDNA) studies of both modern human groups and several short Neandertal and early Upper Paleolithic modern human mtDNA sequences, more scientists have embraced the extreme replacement model. Although the extreme positions may be easiest to characterize, a wide range of hypotheses exist regarding the degree of potential interbreeding between Neandertals and populations of early moderns outside of Europe.
The argument involves three primary pieces of data: skeletal morphology, technological industries, and population genetics. Replacement models have their history in the erroneous description of La Chapelle by Boule and the initial discoveries of early modern humans that were thought to be direct ancestors of modern Europeans (for example, Galley Hill and Grimaldi). The contemporaneity of the Neandertals and early moderns led to the development of the Presapiens Hypothesis proposed by Boule and Sir Arthur Keith and later developed by Henri Vallois. The hypothesis posited that the lineage leading to Neandertals and the lineage leading to modern humans split early in the Pliocene (between 5–2 mya) and diverged along separate evolutionary trajectories. As newer finds were excavated and some older finds were shown to be misdated or fraudulent (such as Piltdown), the Presapiens Hypothesis gave way to the PreNeandertal Hypothesis, which suggested a more recent split just before the last glacial. The fundamental point of both theories was that early moderns and Neandertals coexisted in Europe at the same time. Thus, the Neandertals could not be ancestral to early modern humans.
During this time, following in the intellectual footsteps of researchers such as Carleton Coon and Ales Hrdlièka that pointed out affinities between Neandertals and later Europeans, Franz Weidenreich proposed a multiregional theory of human evolution. Weidenreich suggested that a single ancient form ancestral to all modern humans (and Neandertals) had spread across the Old World and had adapted to its own environments while sharing enough gene flow to maintain a single species, developing differences that are seen in geographic races today. In this candelabra view of human evolution, Neandertals are simply an ancient race of modern human beings that are directly ancestral to the population sharing the same geography as them, modern Europeans. In response, William Howell proposed the “Noah’s Ark” model in which all modern humans developed from a more recently evolved form in Africa that then spread around the Old World, replacing indigenous ancient humans (such as the Neandertals).
In the 1960s and 1970s, the debate took on much of its modern form. Loring Brace pointed out that many of the apparent morphological differences between Neandertals and modern humans were not as extreme as some had claimed and that many of the features could be related to relaxation of evolutionary pressures to maintain robust structures via the development of more advanced technology. In Brace’s arguments, Neandertals developed Upper Paleolithic technology and cooking technology that led to gracilization of cranial form that put them on a trajectory toward modern Europeans, not necessarily requiring any gene flow from “more advanced” forms from Africa and West Asia. Following Brace, Milford Wolpoff restated Weidenreich’s multiregional model, focusing on regional characteristics seen in modern human populations and arguing that these differences appeared first in the regional Homo erectus populations and gene flow between regions maintained species integrity, ensuring that evolutionary trends were shared between all human populations. Shortly afterward, a group of researchers such as Christopher Stringer and Günter Braüer became convinced that the differences between modern humans and Neandertals were too great to be the result of “short” term evolution during the Middle to Upper Paleolithic transition. These researchers published a number of works highlighting the differences between Neandertals and early moderns that showed that the modern human cranial form appeared first in Africa and spread into Europe, replacing the Neandertals. The Out of Africa and Multiregional model battle lines were firmly drawn at this stage. The proponents of replacement focused on the differences between Neandertals and moderns and argued that these differences were too great for the time period that it would take for the evolution from one to the other; they believed that the earliest modern forms occurred in Africa. The proponents of continuity focused on the similarities between the Neandertals and later modern humans and argued that there was a clear evolutionary trend leading from one to the other.
If we are to objectively analyze the relationship of Neandertals to the early moderns that succeeded them, we must review several pieces of paleontological and archaeological evidence.
- With regards to technology, Neandertals are known to have created the Châtelperronian industry, meaning that they were capable of developing the technology characteristic of the Upper Paleolithic.
- The earliest known modern humans associated with the Aurignacian postdate Neandertals in the geographic regions in which they are found. A number of intermediate sites in the 40,000–30,000 BP range exist where lithic materials are either unassociated with any human remains or are associated with undiagnostic fragmentary material such as isolated teeth. Some researchers have claimed these show Neandertal affinities and, alternatively, some have claimed they show modern human affinities. However, these remains are not diagnostic to group affiliation, making their use in either argument unconvincing.
- Site usage patterns are often extremely similar in Middle and early Upper Paleolithic sites, as are subsistence patterns.
- Early Upper Paleolithic modern humans show a variety of morphological characteristics that are unknown or rare among the few earlier African modern forms or in the early anatomically modern human forms from Qafzeh and Skhu – l in West Asia but are widespread in Neandertals. These same features decrease in frequency through the Upper Paleolithic, Mesolithic, and Neolithic until they are rare or nonexistent in Europeans today.
- The rate of evolutionary change needed to go from the Neandertal form to the early Upper Paleolithic modern human form is less than is known in the same features among later European moderns. Essentially, the time needed to evolve the modern form from the Neandertal form is a non sequitur, because it is based not on the differences between Neandertals and their immediate successors, but rather on either non-European contemporaries or modern Europeans.
- A factor rarely considered is the glaciation cycle in Europe and the effect it had on depopulation in Europe. The Neandertals “disappeared” from much of Central and Eastern Europe during a time of extreme glaciation, and a similar gross reduction in human populations in Europe occurred during the last glacial maximum in the Mesolithic. These facts are difficult for the replacement without interbreeding models to deal with, as they seem to point toward Neandertals evolving toward the modern condition, perhaps with strong influx of non-European moderns during the last few interstadials when the ice sheets receded, exposing Europe to colonization with a much reduced indigenous Neandertal population. While comprehensive analysis of the archaeology and anatomy does seem to support the continuity argument, the development of the mtDNA data revolutionized the debate and shifted the consensus opinion squarely to the replacement camp, and created data that are particularly difficult for multiregionalists to satisfactorily explain.
In 1987, the journal Nature published a paper by three molecular biologists who argued that the known restricted variation in modern human mtDNA could be interpreted to mean that the ancestors of modern humans went through a genetic bottleneck in Africa between 280,000 and 140,000 years ago, and then spread throughout the rest of the world without intermixing with indigenous populations. The analysis was attacked on a number of grounds, but further analysis of mtDNA variation and distribution supported the initial claims, with only slight modification of the dates involved. The replacement proponents took this data as unequivocal support for the Out of Africa model of human evolution. In 1997, a small sequence of mtDNA was recovered and amplified from the original Feldhofer Neandertal individual by Svante Pääbo and colleagues. The variation in the sequence was at the very edge of known modern human variation and statistically supported a split between the lineage leading to Neandertals and the lineage leading to modern humans between about 690,000 and 550,000 BP. Samples from several other Neandertal specimens and a few early modern humans were recovered that seem to strongly support the contention of an early split between the two lineages.
For many, this definitively answers the question of Neandertal ancestry for modern humans,with the new question how and why they became extinct. Scientists and researchers have put forth a number of arguments, including violent replacement of Neandertals by invading moderns, deteriorating conditions resulting in the decline of the Neandertals and the expansion of moderns into their previous geographic range, and indirect competition between the more behaviorally “primitive” Neandertals and the more “advanced” moderns leading to a decline and extinction of the Neandertal clade. Some researchers propose that absolutely no interbreeding occurred between populations, while others accept statistically insignificant interbreeding as a possibility, and others propose a “genetic swamping” of Neandertal genes by the much greater numbers of moderns leading to the eventual extinction of Neandertal mtDNA lineages rather than a complete lack of Neandertal ancestry for modern humans. This last position is functional similar to many multiregional models but differs on the issue of evolutionary trends toward modernity within the Neandertals and the degree of gene flow during earlier eras that link the two populations as species.
The debate is not so easily resolved, however, and many multiregionalists point to the fact that much of modern human nuclear DNA does not show the same pattern of extreme bottlenecking traceable to approximately 200,000 years ago. A number of analyses have given nuclear DNA coalescence dates much closer to one million years or more. Molecular geneticists have, however, attacked these analyses, and it is unclear whether they support multiregional claims. A greater problem with the molecular data is the nature of the data themselves. Studies on mtDNA bottlenecks are analyses of variation within particular sequences that have relatively well-known mutation rates. A coalescence date is determined by working backward from the variation seen in a population, presuming a constant mutation rate, to a single sequence with no variation. From the number of mutations needed and a generation time, we may calculate a time range. This method necessarily is unable to deal with the biological reality of expanding and retracting variation of varying strengths throughout evolution or stasis created from relatively stable population levels. The analytical method works best for evaluating the situation it is modeled after: a period of much reduced variation followed by a relatively stable period of expansion in variation to the modern level of variation. While the molecular procedures and analytical methods are becoming more advanced and providing greater confidence in the results themselves, the continuing question of many multiregionalists is what the significance of the results actually are in the context of complex population genetics.
Neandertals were the first nonhuman hominids discovered and have been the focus of some of the most strident debate in paleoanthropology. A seemingly endless number of morphological features, cultural characteristics, and, in modern times, genetic analyses have been used to either differentiate them from modern humans or include them as an ancient variant that contributed to modern humans. Often the questions asked about them are less a reflection of objective scientific inquiry about an extinct human population than a reflection of the most basic question in anthropology: What makes us human?
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- Schwartz, J. H., & Tattersall, I. (2002). The human fossil record, volume 1. Terminology and craniodental morphology of genus Homo (Europe). New York:Wiley-Liss.
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