[Paleopsych] NYT: For Neanderthals and Homo Sapiens, Was It De-Lovely?

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For Neanderthals and Homo Sapiens, Was It De-Lovely?
http://www.nytimes.com/2005/02/15/science/15nean.html
February 15, 2005

    By JOHN NOBLE WILFORD

    The scientists did not get around to the nitty-gritty question until
    the fourth hour of a two-and-a-half-day symposium on Neanderthals,
    held recently at New York University.

    A strong consensus was emerging, they agreed, that the now-extinct
    Neanderthals were a distinct evolutionary entity from modern humans,
    presumably a different species. They were archaic members of the human
    family, robust with heavy brow ridges and forward-projecting faces,
    who lived in Europe and western Asia from at least 250,000 years ago
    until they vanished from the fossil record about 28,000 years ago.

    Neanderthals may have seen their first modern Homo sapiens some
    100,000 years ago in what is now Israel. The two people almost
    certainly came in contact in Europe in the last centuries before the
    dwindling Neanderthal population was replaced forever by the intruding
    modern humans.

    Taking his turn at the symposium lectern, Dr. James C. M. Ahern, a
    paleoanthropologist at the University of Wyoming, acknowledged:
    "Neanderthals are different. The degree of difference is relatively
    vast, but that is not the most interesting question out there."

    The question was, he continued, "Did Neanderthals and modern humans do
    it?"

    There it was, out in the open again, the question that has persisted
    since the first fossils of these people were discovered in the Neander
    Valley of Germany in 1856. Could the two people with a shared distant
    ancestry and family resemblance have interbred? Is there any evidence
    that Europeans today carry some Neanderthal genes?

    For the international gathering of scientists, the issue exposed the
    uncertainty over the definition of species. Its conventional meaning
    is a group of interbreeding creatures that are reproductively isolated
    from others. Hybridization of species is rare in mammals. One common
    example is the mating of an ass and a mare, producing the sterile
    mule.

    The conferees debated, but never resolved, the possibility that
    Neanderthals could have been an evolutionary and anatomical species,
    distinct from Homo sapiens, but not strictly an isolated biological
    species. That is, the two species may have been enough alike to mate
    and produce fertile offspring.

    Again, Dr. Ahern encapsulated the issue, "How much difference is too
    much" for viable interbreeding to occur?

    Dr. Chris Stringer, a paleontologist at the Natural History Museum in
    London, noted that some species apparently less close than
    Neanderthals and modern humans can interbreed and produce hybrids. Dr.
    Stringer is a leading proponent of the theory that modern Homo sapiens
    emerged in Africa as early as 150,000 years ago and then spread to
    Asia and Europe, replacing the remnants of archaic humans they
    encountered there.

    Dr. Erik Trinkaus, a Neanderthal expert at Washington University in
    St. Louis, who was not at the meeting, contends that the
    24,500-year-old skeleton of a young boy found in Portugal appeared to
    be a Neanderthal-Homo sapiens hybrid. The interpretation has so far
    been viewed with skepticism.

    Dr. Mark Stoneking of the Max Planck Institute for Evolutionary
    Anthropology in Leipzig, Germany, said that he and colleagues had
    looked for answers in the patterns of genetic variation in
    contemporary human populations and the analysis of ancient DNA from
    fossils of Neanderthals and early modern humans. Neither approach, he
    said, provided any indication of interbreeding between the two
    species.

    "That does not rule out some genetic contribution" from Neanderthals
    to Europeans' ancestry, Dr. Stoneking said.

    Dr. David Serre of McGill University in Montreal described the
    analysis of the maternally inherited mitochondrial DNA found in 24
    Neanderthals and 40 early modern human remains. The results seemed to
    exclude any significant contribution of Neanderthal genes to Homo
    sapiens, perhaps less than 1 percent. Therefore, he concluded, they
    were "two distinct biological species."

    Dr. Katerina Harvati, also of the Planck Institute in Leipzig,
    recently conducted research applying a "quantitative method" to
    determine the degree of anatomical difference that justifies
    classifying specimens as different species. She and colleagues
    examined the variation of specific parts of the craniums and faces of
    modern humans and Neanderthals as well as 12 existing species of
    nonhuman primates. The two living species of chimpanzees, for example,
    appeared to be more closely related to each other than Neanderthals
    are to humans.

    Dr. Harvati and Dr. Terry Harrison, a paleontologist at N.Y.U.,
    organized the symposium, "Neanderthals Revisited: New Approaches and
    Perspectives."

    More than species differences may have kept Neanderthals and humans
    sexually apart, if indeed that was the case. Their opportunities may
    have been limited.

    Dr. Ahern said in an interview that it was "surprising how little
    overlap there was" between the two species in Europe." It had been
    thought that modern humans from Africa began arriving in Europe about
    40,000 years ago and so could have competed with and mingled with the
    local population for at least 12,000 years. But the dating of fossil
    and archaeological evidence is now being revised, leaving much less
    time when the two species could have had close contact.

    "It's a real scientific problem," said Dr. Randall White, an
    archaeologist specializing in European ice age culture at N.Y.U. "How
    to interpret the overlap of Neanderthals and modern humans, their
    interactions and cultural exchanges, the causes of Neanderthal
    extinction, all depends on what are the real dates of their possible
    contact."

    Some of the most solid evidence for overlap, the researchers said,
    does not appear until toward the end of the Neanderthals' known
    existence, when their populations were probably sparse.

    Dr. Stringer said some explanations for Neanderthal extinction were
    being re-examined. Perhaps the technological superiority of modern
    humans was "not as clear-cut as some of us thought," he said. Perhaps
    Neanderthals, though adapted to a cold climate, could not survive the
    rapid and repeated changes of cold and warm periods of that time.

    "It was not bad genes but bad luck for the Neanderthals," Dr. Stringer
    said. "Modern humans may have had no direct effect on Neanderthal
    extinction. They actually walked into empty spaces where Neanderthals
    had already disappeared."

    Dr. Ian Tattersall of the American Museum of Natural History was not
    entirely joking when he suggested that few genes were exchanged
    because "no self-respecting Neanderthal female would fancy a Homo
    sapiens male."

    In making a case for the distinct differences between the two species,
    Dr. Tattersall showed slides of upright skeletons of the two. But
    skeletons are unrevealing of Paleolithic desire.