[Paleopsych] SW: Neanderthals and the Colonization of Europe

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Anthropology: Neanderthals and the Colonization of Europe

     The following points are made by Paul Mellars (Nature 2004 432:461):
     1) The most significant contributions over the past decade to the
     study of the fate of the Neanderthals have come from detailed studies
     of the DNA structure of present-day human populations in different
     areas of the world, combined with the gradually accumulating recovery
     of residual traces of "ancient" DNA extracted from a number of
     Neanderthal and early anatomically modern human remains. Studies of
     both mitochondrial and Y-chromosome DNA patterns in modern world
     populations (inherited respectively through the female and male
     lineages) point to the genetic origins of all present-day populations
     within one limited area of Africa somewhere in the region of 150,000
     years before present (yr BP), followed by their dispersal to other
     regions of the world between about 60,000 and 40,000 yr BP(1-5).
     2) These results are further reinforced by recent discoveries of
     skeletal remains of anatomically modern populations in different
     areas. Discoveries at Herto in Ethiopia reported in 2003 confirm the
     presence of early forms of anatomically modern humans in Africa by
     about 160,000 yr BP, whereas the earliest discoveries of distinctively
     modern populations in both Europe and most parts of Asia can be dated
     no earlier than 40,000-45,000 yr BP. The one exception is in Israel,
     where the rich skeletal remains from the Skhul and Qafzeh caves
     indicate a precocious, and apparently short-lived, incursion of early
     anatomically modern populations into this region (presumably via the
     Nile valley) at an early stage in the last glaciation, around 100,000
     yr BP.
     3) In Europe, the most dramatic support for these patterns has come
     from the recovery of a number of relatively well-preserved sequences
     of mitochondrial DNA from a number of actual skeletal finds of
     Neanderthals and early anatomically modern humans. Analyses of seven
     separate Neanderthal specimens (including those from the Neanderthal
     type-site itself) yielded segments of mitochondrial DNA that are
     radically different from those of all known present-day populations in
     either Europe or other parts of the world, and that are equally
     different from those recovered from five early specimens of
     anatomically modern populations from European sites. The conclusion is
     clear that there was either very little -- if any -- interbreeding
     between the local Neanderthals and the intrusive modern populations in
     Europe, or that if such interbreeding did take place, all genetic
     traces of this interbreeding were subsequently eliminated from the
     European gene pool.
     4) The mitochondrial DNA evidence recovered from the Neanderthal
     specimens further suggests that the initial evolutionary separation of
     the Neanderthals from the populations which eventually gave rise to
     genetically modern populations must reach back at least 300,000 yr --
     a finding that is in good agreement with the surviving fossil evidence
     from Africa and Europe1. Whether this evidence is sufficient to
     indicate that the Neanderthals belonged to an entirely separate
     biological species from modern humans is at present more
     5) The fate of the Neanderthal populations of Europe and western Asia
     has gripped the popular and scientific imaginations for the past
     century. Following at least 200,000 years of successful adaptation to
     the glacial climates of northwestern Eurasia, they disappeared
     abruptly between 30,000 and 40,000 years ago, to be replaced by
     populations all but identical to modern humans. Recent research
     suggests that the roots of this dramatic population replacement can be
     traced far back to events on another continent, with the appearance of
     distinctively modern human remains and artefacts in eastern and
     southern Africa.
     6) That the Neanderthals were replaced by populations that had evolved
     biologically, and no doubt behaviorally, in the very different
     environments of southern Africa makes the rapid demise of the
     Neanderthals even more remarkable, and forces us to ask what cultural
     or cognitive developments may have made this replacement possible. The
     rapidly accumulating archaeological evidence for highly symbolic
     patterns of culture and technology within African populations dating
     back to at least 70,000 yr BP (marked by the appearance of complex
     bone technology, multiple-component missile heads, perforated
     sea-shell ornaments, complex abstract "artistic" designs and abundant
     use of red ochre --recently recorded from the Blombos Cave and other
     sites in southern Africa) may provide the critical clue to new
     patterns of cognition, and probably complex linguistic communication,
     linked directly with the biological evolution of anatomically and
     genetically modern populations(1,3). Perhaps it was the emergence of
     more complex language and other forms of symbolic communication that
     gave the crucial adaptive advantage to fully modern populations and
     led to their subsequent dispersal across Asia and Europe and the
     demise of the European Neanderthals. The precise mechanisms and timing
     of this dramatic population dispersal from southern Africa to the rest
     of the world remains to be investigated(1,3,4).
     References (abridged):
     1. Stringer, C. Modern human origins: progress and prospects. Phil.
     Trans. R. Soc. Lond. B 357, 563-579 (2002)
     2. Tattersall, I. in The Speciation of Modern Homo sapiens (ed. Crow,
     T. J.) 49-59 (British Academy, London, 2002)
     3. Forster, P. Ice ages and the mitochondrial DNA chronology of human
     dispersals: a review. Phil. Trans. R. Soc. Lond. B 359, 255-264 (2004)
     4. Lahr, M. M. & Foley, R. Towards a theory of modern human origins:
     geography, demography and diversity in modern human evolution. Yb.
     Physical Anthropol. 41, 127-176 (1998)
     5. Richards, M. et al. Tracing European founder lineages in the near
     Eastern mitochondrial gene pool. Am. J. Hum. Genet. 67, 1251-1276
     Nature http://www.nature.com/nature
     Related Material:
     The following points are made by Pat Shipman (American Scientist 2004
     1) Neandertals (Neanderthals) were probably not members of our own
     species, judging from recent analyses of mitochondrial DNA.
     Nonetheless, Neandertals were clearly built on a human-like plan (or
     vice versa) with some crucial modifications. A glance at the fossil
     remains of these hominids shows that Neandertal bones are much more
     robust than those of modern Homo sapiens. The skulls of the two
     species also show several striking differences. One of the most
     noticeable Neandertal features is the unmistakably large, bony
     browridges that stick out over the eyes. Below the orbits, the face is
     more prognathic -- the nose and jaw protrude farther in front of the
     braincase -- than a human face. The prominent nasal bones in
     Neandertal skulls top wide nasal openings, suggesting that they
     sported large, aquiline noses. Unlike the smoother, rounded contour of
     the human skull, the back of the Neandertal skull has a distinctive
     bulge, often referred to as a chignon or bun. Overall, the Neandertal
     skull resembles what you might expect if someone took a human skull
     made of rubber, grabbed it by the face and back of the head, and
     2) These comparisons have attracted the attention of researchers who
     study the interactions between evolution and development from birth to
     adulthood -- so-called "evo-devo." Put simply, they wanted to know:
     How do you grow up Neandertal? In the spring of 2004, several studies
     offered answers to this question. F. Ramirez Rozzi and J.M. Bermudez
     de Castro (1) compared the rates of dental growth in several species
     within the genus Homo, including Neandertals. They examined the
     perikymata -- small enamel ridges on the tooth surface -- of incisor
     and canine teeth from 55 Neandertals, 25 Homo antecessor and Homo
     heidelbergensis individuals (two species that some anthropologists
     group together) and 39 ancient but anatomically modern humans.
     3) Perikymata are created as a tooth grows. In humans and their close
     kin (such as Homo erectus), one ridge is created approximately every
     nine days during tooth development. The ridges of more distant
     relatives, including chimpanzees and gorillas, are formed at shorter
     intervals. By counting the number of perikymata, investigators can
     calculate how long the tooth took to form. Ramirez Rozzi and Bermudez
     de Castro (1) found that Neandertals formed their teeth in fewer days
     than did H. antecessor and H. heidelbergensis. If Neandertals had been
     the most ancient of the lot, one might expect them to be the most
     ape-like. But although the other fossil species are older still, they
     already show the human pattern. The finding is also a surprise because
     some researchers still propose that Neandertals are basically just
     strange-looking humans -- a judgment challenged by this fundamental
     4) Dental maturity is a common proxy for overall maturity because
     neurological, skeletal and sexual milestones are correlated with the
     pace of tooth mineralization. Ramirez Rozzi and Bermudez de Castro (1)
     concluded that faster dental development meant that Neandertals
     reached adulthood 15 percent sooner than humans, on average. To state
     this finding in practical terms, if humans attain physical maturity at
     18 years, Neandertals were similarly grown at 15 years. The study also
     examined the spacing of perikymata across the front surfaces of
     incisors and canines. Dental enamel forms first at the tip of the
     crown -- the first point to emerge from the gum -- and then proceeds
     toward the roots.
     5) In modern humans, the perikymata are widely spaced in the half of
     the tooth that formed first, indicating that lots of enamel was
     deposited during each nine-day increment. On the second half of each
     human tooth, the ridges are more closely spaced, showing a slower
     daily rate of enamel formation. Like human teeth, Neandertal teeth
     look as if they grew rapidly at first and then slowed down. However,
     on the part of each Neandertal tooth that grew later, the perikymata
     are more spread out than in their human counterparts. In other words,
     although the rate of enamel formation also decreased with age in
     Neandertals, the slowdown was less pronounced. This pattern of dental
     growth resembles that of apes. We know that the apes of today reach
     physical maturity much faster than humans. So, presumably, did
     References (abridged):
     1. Krovitz, G. 2003. Shape and growth differences between Neandertals
     and modern humans: Grounds for species-level distinction? In Patterns
     of Growth and Development in the Genus Homo, ed. J. L. Thompson, G. E.
     Krovitz and A. J. Nelson. Cambridge, UK: Cambridge University Press
     2. Ramirez Rozzi, F., and J. M. Bermudez de Castro. 2004. Surprisingly
     rapid growth in Neanderthals. Nature 428:936-939
     3. Trinkaus, E. 1995. Neandertal mortality patterns. Journal of
     Archaeological Science 22:121-142
     4. Williams, F. L., L. R. Godfrey and M. R. Sutherland. 2003.
     Diagnosing heterochronic perturbations in the craniofacial evolution
     of Homo (Neandertals and modern humans) and Pan (P. troglodytes and P.
     paniscus). In Patterns of Growth and Development in the Genus Homo,
     ed. J. L. Thompson, G. E. Krovitz and A. J. Nelson. Cambridge, UK:
     Cambridge University Press
     American Scientist http://www.americanscientist.org
     Related Material:
     The following points are made by Alan Cooper et al (Current Biology
     2004 14:R431):
     1) The genetic affinities of the earliest modern humans of Europe and
     the earlier hominid occupants of the area, the Neandertals, has
     remained a hotly debated topic since the discovery of the
     extraordinarily robust skull cap and limb bones in the Neander Valley
     in 1856. While it is impossible to rule out a surreptitious coupling
     of the two groups in the more than 10,000 years they apparently
     co-occupied Europe, recent research and population genetic theory
     suggest that any genetic interchange was limited.
     2) This issue is central to the two main theories of modern human
     origins: the replacement model, where modern humans rapidly replaced
     archaic forms, such as Neandertals, as they began to spread from
     Africa through Eurasia and the rest of the world sometime around
     100,000 years ago [1]; and the multi-regional model, where genetic
     exchange or even continuity exists between archaic and modern humans
     [2,3]. Two years ago, a review [4] reported that characteristic
     mitochondrial DNA (mtDNA) sequences retrieved from remains of four
     Neandertals are absent from modern human populations. It remained
     possible, however, that these sequences had been present in early
     modern humans, but had been lost through genetic drift or the
     continuous influx of modern human DNA in the intervening 28,000 years
     since Neandertals became extinct.
     3) The difficulty in testing these ideas using ancient DNA is that
     most ancient human remains are contaminated with modern human DNA,
     which deeply penetrates bone and teeth samples during the washing and
     routine handling that takes place after excavation. This modern DNA
     will either out-compete authentic ancient sequences in PCR reactions,
     or recombine with them to produce artificial, but authentic looking
     genetic sequences [5]. Consequently, even when strict criteria for
     authenticating ancient DNA results are followed, it can be impossible
     to determine the authenticity of results.
     4) The approach taken recently by Serre et al [2004] avoided this
     problem by searching only for the presence of Neandertal mtDNA
     sequences in both early modern human and Neandertal fossils, while
     ignoring modern human sequences because they are potentially
     contaminants. Four additional Neandertal specimens tested positive,
     but Neandertal sequences could not be detected in five early modern
     human fossils with biochemical preservation consistent with DNA
     survival from the Czech Republic and France. This appears to confirm
     that sequences characteristic to Neandertal remains were not
     widespread in early modern humans.
     5) In summary: Mitochondrial DNA sequences recovered from eight
     Neandertal specimens cannot be detected in either early fossil
     Europeans or in modern populations. This indicates that if Neandertals
     made any genetic contribution at all to modern humans, it must have
     been limited, though the extent of the contribution cannot be resolved
     at present.
     References (abridged):
     1. Stringer, C.B. and Andrews, P. (1998). Genetic and fossil evidence
     for the origin of modern humans. Science 239, 1263-1268
     2. Hawks, J.D. and Wolpoff, M.H. (2001). The accretion model of
     Neandertal evolution. Evol. Int. J. Org. Evol. 55, 1474-1485
     3. Templeton, A. (2002). Out of Africa again and again. Nature 416,
     4. Schmitz, R.W., Serre, D., Bonani, G., Feine, S., Hillgruber, F.,
     Krainitzki, H., Poobo, S., and Smith, F.H. (2002). The Neandertal type
     site revisited: interdisciplinary investigations of skeletal remains
     from the Neander Valley, Germany. Proc. Natl. Acad. Sci. USA 99,
     5. Poobo, S., Higuchi, R.G., and Wilson, A.C. (1989). Ancient DNA and
     the polymerase chain reaction. J. Biol. Chem. 264, 9709-9712
     Current Biology http://www.current-biology.com

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