Ancient human interbreeding

From: Glenn Morton (glennmorton@entouch.net)
Date: Tue Jun 17 2003 - 15:58:59 EDT

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    I have long argued that there is good, indisputable evidence for genes from
    Neanderthals and other ancient hominids in the genomes of modern
    populations, see http://www.glenn.morton.btinternet.co.uk/hegene.htm

    This view is not the darling of the press, and is objected to by many
    christians who want to have Adam and Eve associated with the mitochondrial
    Eve of genetics. This Eve lived somewhere between 0 and 800,000 years ago
    but the most likely time frame is 100-200 kyr ago. This gives the old earth
    creationists a place to neatly fit Eve into the fold. Several authors take
    this approach. David Wilcox believes this and says so in his PSCF article

    "Both cultural and physical evidence suggests an abrupt establishment of the
    image about 100,000 years ago." ~ David L. Wilcox, "Adam, Where Are You?
    Changing Paradigms in Paleoanthropology," Perspectives on Science and
    Christian Faith , 48:2( June 1996), p. 94

    Robert Newman takes this position, specifically citing the mtDNA evidence as
    being indicative of the origin of humanity:

    žOne Christian, Glenn Morton, puts the origin of the human race back several
    million years ago with the Australopithicines; at the other extreme is Dick
    Fischer, who places the origin of humans about five thousand years ago with
    Adam, but not as the progenitor of the entire human race. I am closer to
    Hugh Ross, who sees the creation of Adam as some tens of thousands of years
    ago, which seems to fit the evidence from mitochondrial Eve and Y-chromosome
    Adam better than MortonŪs view, and the biblical teaching of Adam as our
    forefather better than FischerŪs. I am closest to the position of John
    Bloom.Ó Robert C. Newman, žConclusionÓ in J. P. Moreland and John Mark
    Reynolds, editors, Three Views on Creation and Evolution, (Grand Rapids:
    Zondervan, 1999), p. 154-155

    Hugh Ross twists the mitochondrial Eve to fit his preconceived idea of Adam
    and Eve being no older than 60,000 years (Hugh Ross, "Chromosome Study Stuns
    Evolutionists," Facts & Faith, 9:3,(1995) p. 3). There simply is not way
    that one can fit the genetics of humanity in to the past 60,000 years. All
    these efforts forget that the history of one gene system is not the history
    of the population. If it were, then every single gene system analyzed would
    yield the same age. They don't.

    As mentioned above, the studies show a wide range of time frames for which
    mitochondrial Eve and Y-chromosome Adam could have lived. Clark writes:

            žThis research produces estimates of the age of the most
    recent human mtDNA
    ancestor that range from 0 to 806,000 years (95% confidence interval, data
    from 12 studies postdating 1991). Coalescence estimates of modern human
    ancestry based on Y-chromosome and nDNA polymorphism data (11 studies
    postdating 1993) range from 62,000 to 1,300,000 years. " G. A. Clark,
    žComments,Ó Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó Current
    Anthropology, 43(2002):5:749-774, p. 765

    Obviously, this doesn't fit the preconceptions of those authors above all of
    whom prefer a younger Adam and Eve. But the data I present on my page
    http://www.glenn.morton.btinternet.co.uk/hegene.htm has gene systems which
    are considerable older than even this. The age is calculated for these
    systems by the length of time it would take for the alleles to accumulate
    the number of mutations which are observed. Young genes have few mutations
    and old genetic systems have lots of mutations.

    But in spite of this evidence, the Out of Africa viewpoint has dominated
    anthropology. This is the theory that modern humans arose in Africa and
    replaced all the archaic populations around the world. They cite the mtDNA
    data as support for their view, claiming that there is no way that
    multiregionalism (the view that there was interbreeding between the archaics
    and the modern humans) can explain the features seen in modern humans.
    These are, low genetic diversity in most gene systems, low effective
    populations and indications of a population bottleneck at some places in the
    genome.

    Now, Vinayak Eswaran writing in Current Anthropology (Dec 2002 pp 749-774)
    presents a numerical model of a selectively advantageous multi-gene system
    which moves out in a wave across the land spreading the advantageous genes
    without having any migration.

    Eswaran writes:
    žThis mechanism is investigated using a quantitative model that suggests
    explanations for many puzzling aspects of the genetic fossil, and
    archaeological data on modern human origins. The data indicate significant
    genetic assimilation from archaic human populations into modern ones.Ó
    Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó Current Anthropology,
    43(2002):5:749-774, p. 749

    and

            žIn this paper I suggest that most of the features associated with
    anatomical modernity evolved in Africa as a coadapted gene combination (or
    žgenotypeÓ) and spread across the world because they collectively offered
    some strong selective advantage. The development of such a genotype can
    quite plausibly be based on the shifting-balance theory of Sewall Wright
    (1932). WrightŪs theory suggests that, in populations subdivided into small
    semi-isolated demes, evolution can occur in the following three phases: (1)
    Genetic drift propels different demes along different trajectories,
    facilitating an exploration of the adaptive landscape available to the
    species. (2) Intrademe selection allows some demes to reach a new and higher
    adaptive peak. (3) Interdeme selection propagates the gene combinations that
    correspond to these adaptive advances and shifts the entire species to the
    new peak. For all this to occur, the demes are required to be (a) small
    enough to allow significant genetic drift and (b) semi-isolated, to
    facilitate the formation of complex coadapted gene combinations that would
    otherwise be broken up by admixture.Ó Vinayak Eswaran, žA Diffusion Wave Out
    of Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 750

    and

            žIt is proposed below that the modern morphology may itself
    have given the
    advantage, possibly due to lowered childbirth mortality, that propagated
    anatomical modernity.Ó Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó
    Current Anthropology, 43(2002):5:749-774, p.751

    and

            žThis theory thus suggests, in contrast to the recent
    African-origin model,
    that the emergence of modern humans was not a speciation but an intraspecies
    žcharacter changeÓ (Wright 1982).Ó Vinayak Eswaran, žA Diffusion Wave Out of
    Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 751

    He suggests that childbirth mortality was reduced by the modern form but
    that is a controversial suggestion. The important thing is that anything
    that gave a selective advantage could spread the modernity genes. He
    describes the way the diffusion wave works:

            žEthnographic studies of present-day hunter-gatherers suggest an
    interbreeding rate of around 0.05. This value of mo with an assumed
    a=0.07/generation would allow a diffusion wave of modernity to spread at a
    rate compatible with the fossil recordůtraveling a distance of 11,000 km or
    so in 4,000 generations. Recall that a is the relative growth rate in a
    generation of, say, 20 years.Ó Vinayak Eswaran, žA Diffusion Wave Out of
    Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 755

    and

    žThe simulations show the wave front to be barely 800 km in width, and the
    region within which clear signs of hybridization would have appeared could
    have been as narrow as 300 km. Hybrids ahead of this narrow region were
    close to archaic, while those behind were essentially modern. Thus if the
    diffusion wave traveled through 3,000 km of Europe between 45,000 and 25,000
    years ago, only 10% of the fossils of that period could be expected to have
    clearly mixed morphologyůwhich may explain the rarity of obvious hybrids in
    the fossil record.Ó
            žAnother empirical observation that could be explained by
    these simulations
    is the relatively rapid transition that has been recorded to occur at the
    local level. The transition from ŽprogressiveŪ archaic to ŽessentiallyŪ
    modern could have taken as little as 2,000 to 3,000 years, the time required
    for the 300-km core of the wave front to pass over a site.Ó Vinayak Eswaran,
    žA Diffusion Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774,
    p.757

    Note that in this model, there is no replacement, merely a character change.
    There is interbreeding which explains the genes listed on my web page,
    explains the fact that the red-headed gene seems to have been inherited in
    modern European populations from the Neanderthals (see
    http://www.calvin.edu/archive/asa/200201/0288.html). The theory also
    explains why there is such a low genetic diversity in humans compared with
    most other species.

            žThe wave-front bottlenecks and the consequent homogenization
    could explain
    why genetic diversity is low in human populations, as are the apparent
    coalescence times for some loci [particularly in mtDNA and Y-chromosome
    studies], and why so small a number as around 10,000 individuals has been
    estimated by many geneticists as the effective size of the modern human
    lineage. The diffusion-wave theory thus offers an alternate explanation for
    these empirical observations that have generally been interpreted as support
    for the recent-African origin replacement model.Ó Vinayak Eswaran, žA
    Diffusion Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774,
    p.759-760

      (I must note that this low diversity can't be due to a recent origin of
    humanity so long as there are genetic systems which would have taken
    millions of years to generate the observed number of alleles in humanity.
    One such system is the Major Histocompatibility Complex (MHC) which shows no
    population bottleneck for tens of millions of years)

    and

            žThe genetic diversity of present-day Africans at neutral DNA loci has
    usually been found to be higher than in all other populations. This is
    usually seen as support for the recent-African-origin model. However, in the
    present theory, the same empirical observation is expected from the core
    region, where the modern genotype first evolved and modern humans have the
    deepest roots.Ó Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó Current
    Anthropology, 43(2002):5:749-774, p. 760

    But would the 'bottleneck' phenomenon preclude the high-diversity ancient
    genes? No. Eswaran says:

            žIt is already been argued above that unique African neutral
    alleles being
    carried by the diffusion wave front would have developed the typical
    symptoms of bottlenecked populations, leading to significant allele loss.
    However, with ancient and widespread polyporphisms there would also have
    been the possibility of allele replenishment through assimilation from
    archaic populations, for the same polymorphisms, so to speak, would have
    been found in both modern and archaic humans.Ó Vinayak Eswaran, žA Diffusion
    Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 761

    One thing I really like about Current Anthropology is that there are always
    reviewers to tell you what is wrong the the theory immediately. The
    reviewers criticized Eswaran's suggestion thatpelvis shape change was the
    reason for decreased infant mortality. They criticised him for appearing to
    think that his wave was the only process which occurred, but no one said his
    theory wouldn't work. Harpending wrote:

            žThis paper will quickly become a central part of the canon
    of biological
    anthropology. Eswaran starts with a very simple model of the appearance of a
    new advantageous trait complex in a subdivided populationůselective
    advantage along with demic diffusionůand derives a rich variety of
    consequences of the process. The simple model explains the available genetic
    and morphological data better than anything we have had until now and gives
    us many testable predictions.Ó Henry Harpending, žComments,Ó Vinayak
    Eswaran, žA Diffusion Wave Out of Africa,Ó Current Anthropology,
    43(2002):5:749-774, p. 765

    Clark wrote:

            žAs a convinced multiregionalist, I like EswaranŪs paper because it
    proposes a plausible scenario to explain the appearance of modern form
    without the necessity for invoking migration.Ó G. A. Clark, žComments,Ó
    Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó Current Anthropology,
    43(2002):5:749-774, p. 765

    Rosenberg wrote:

            žEswaran offers an intriguing and sophisticated model for the causes of
    morphological change in Upper Pleistocene human evolution and subsequent
    modern genetic diversity.Ó Karen Rosenberg, žComments,Ó Vinayak Eswaran, žA
    Diffusion Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774, p.
    766

    Trinkaus wrote:

    žIn this elegant demonstration, Eswaran has done what has been needed for
    some period of time, he has provided an explicit model with explicit
    assumptions to model the populational and genetic processes by which modern
    human biology may have spread and eventually become the dominant form across
    the Old World.Ó Erik Trinkaus, žComments,Ó Vinayak Eswaran, žA Diffusion
    Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 767

    and

    žI am convinced that the Ždiffusion-waveŪ model was a major player in a
    number of regions and time periods during the process of modern human
    emergence (which, after all, took more than 70,000 years to occur and
    involved all of the inhabited Old Word), but I remain unconvinced that it
    can explain all of the factors to which Eswaran applies it without too heavy
    a dose of special pleading.Ó Erik Trinkaus, žComments,Ó Vinayak Eswaran, žA
    Diffusion Wave Out of Africa,Ó Current Anthropology, 43(2002):5:749-774, p.
    767

    Wolpoff wrote:

    žStill, there is no question that in some form or other EswaranŪs
    diffusion-wave model is quite likely a valid explanation for the
    multiregional pattern of any one of a number of specieswide events in human
    evolutionary history. It is a significant and particularly insightful
    description of how multiregional evolution might be expected to work when a
    specieswide change involves a package of characteristics that have a single
    origin but are related only by the common adaptation they promote.Ó Milford
    H. Wolpoff, žComments,Ó Vinayak Eswaran, žA Diffusion Wave Out of Africa,Ó
    Current Anthropology, 43(2002):5:749-774, p. 769

    Zilhao writes:

            žI cannot but agree with these conclusions, since I have been
    arguing along
    similar lines." Joao Zilhao, žComments,Ó Vinayak Eswaran, žA Diffusion Wave
    Out of Africa,Ó Current Anthropology, 43(2002):5:749-774, p. 769

    Here at last is an explanation for how modernity arose which does not
    require a break between the archaics and moderns. Indeed, it requires
    genetic continuity and it explains the genetic data as one concise theory.
    It doesn't have to ignore the data indicating ancient lineages in some gene
    systems. Christian apologists should take note. They probably won't. It
    seems they rarely do.



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