The Boston Globe

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Date: Tue May 30 2000 - 10:29:32 EDT

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    The Boston Globe, May 30, 2000, Tuesday, Pg. E1
    HEADLINE: A LITTLE FISH CHALLENGES A GIANT OF SCIENCE
    BYLINE: By Fred Heeren, GLOBE CORRESPONDENT

        CHENGJIANG, China The fish-like creature was hardly more than an inch
    long, but its discovery in the rocks of southern China was a big deal. The
    530millionyearold fossil, dubbed Haikouella, had the barest beginning of a
    spinal cord, making it the oldest animal ever found whose body shape
    resembled modern vertebrates.
        In the Nature article announcing his latest findings, JunYuan Chen and
    his colleagues reported dryly that the ancient fish "will add to the debate
    on the evolutionary transition from invertebrate to vertebrate." But the
    new fossils have become nothing less than a challenge to the theory of
    evolution in the hands of Chen, a professor at the Nanjing Institute of
    Paleontology and Geology. Chen argued that the emergence of such a
    sophisticated creature at so early a date shows that modern life forms
    burst on the scene suddenly, rather than through any gradual process.
        According to Chen, the conventional forces of evolution can't account
    for the speed, the breadth, and onetime nature of "the Cambrian explosion,"
    a geologic moment more than 500 million years ago when virtually all the
    major animal groups first appear in the fossil record.
        Rather than Charles Darwin's familiar notion of survival of the
    fittest, Chen said he believes scientists should focus on the possibility
    that a unique harmony between forms of life allowed complex organisms to
    emerge. If all we have to depend upon is chance and competition, the
    conventional forces of evolution, Chen said, "then complex, highly evolved
    life, such as the human, has no reason to appear."
        The debate over Haikouella casts Western scientists in the unlikely
    role of defending themselves against charges of ideological blindness from
    scientists in Communist China. Chinese officials argue that the theory of
    evolution is so politically charged in the West that researchers are
    reluctant to admit shortcomings for fear of giving comfort to those who
    believe in a biblical creation.
        "Evolution is facing an extremely harsh challenge," declared the
    Communist Party's Guang Ming Daily last December in describing the fossils
    in southern China. "In the beginning, Darwinian evolution was a scientific
    theory. . . . In fact, evolution eventually changed into a
    religion." Taunts from the Communist Party wouldn't carry much sting,
    however, if some Western scientists weren't also concerned about weaknesses
    in socalled neoDarwinism, the dominant view of evolution over the last 50
    years.
        "NeoDarwinism is dead," said Eric Davidson, a geneticist and textbook
    writer at the California Institute of Technology. He joined a recent
    gathering of 60 scientists from around the world near Chengjiang, where
    Chen had found his first impressions of Haikouella five years ago.
        But most Westerners at Chen's conference came to praise Darwin, not to
    bury him. The idea that neoDarwinism is missing something fundamental about
    evolution is as scandalous to Americans as it is basic to the Chinese.
        Despite their misgivings about Chen's "harmony" proposal a mysterious
    mix of scientific caution, Chinese philosophy, and a decidedly nonWestern
    lack of concern for Darwinian orthodoxy Western scientists have no choice
    but to go to China to learn about the emergence of animal body plans,
    including that of humans.
        Virtually all of today's living phyla or major animal groups make
    their first impressions in the geologic period known as the Cambrian. And
    Chengjiang, in the southern province of Yunnan, contains the oldest and
    best preserved Cambrian fossils in the world. JunYuan Chen has coauthored
    half of all the papers on the Chengjiang fauna.
        Chen's discovery of the earliest creature with a primitive nervous
    system, called a chordate, is, for him, but one more piece in a puzzle that
    looks less and less like the conventional picture of evolution through
    natural selection.
        For Western paleontologists, Haikouella looks like a breakthrough for
    understanding the origin of the human lineage.
        "It proves that the direct ancestor of mankind already existed in the
    time of the Cambrian explosion," said German paleontologist Michael Steiner.
        "Sort of instinctively, I felt I should go and pay homage to this
    animal," said another scientist at the conference, Nicholas Holland, an
    authority on primitive chordates at the Scripps Institution of Oceanography
    in San Diego. "It's the earliest known chordate ancestor. This is going to
    be page one, two, three and four of vertebrate texts."
        Chen enjoys seeing his fossils get the attention. But to him, the big
    story is not that he has discovered our earliest traceable ancestor but
    that the Cambrian explosion of new body plans is proving to be real, not an
    illusion produced by an incomplete fossil record.
        Because new animal groups did not continue to appear after the Cambrian
    explosion 530 million years ago, he believes that a unique kind of
    evolution was going on in Cambrian seas. And, because his years of
    examining rocks from before the Cambrian period has not turned up viable
    ancestors for the Cambrian animal groups, he concludes that their evolution
    must have happened quickly, within a mere 2 or 3 million years.
        According to Chen, the two main forces of evolution espoused by
    neoDarwinism, natural selection ("survival of the fittest") and random
    genetic mutation, cannot account for the sudden emergence of so many new
    genetic forms.
        "Harmony can be a driving force [of evolution], too," Chen proposed at
    the Chengjiang conference.
        As if to underscore the abruptness of Haikouella's place in the fossil
    record, Chen pointed out the features that make Haikouella look so much
    more advanced than expected for an early Cambrian animal.
        Biologists had been expecting to see something that would look like a
    primitive ancestor to the middle Cambrian animal called Pikaia, formerly
    promoted as the world's earliest chordate. Rather than finding evidence
    that Pikaia had a lesscomplex ancestor, Chen instead found a chordate that
    already displayed many vertebrate characteristics 15 million years earlier.
        And some of the 305 fossil specimens Chen's team has recovered are so
    well preserved that paleontologists practically swoon over them.
        "They're almost like a photograph of the anatomy of the animals," said
    French paleontologist Philippe Janvier.
        But all this newfound clarity only adds to the larger problem, framed
    succinctly by Holland of Scripps Institution: "Where the hell are you going
    to get an animal like that?" In his view, Haikouella's high level of
    development makes it more difficult to explain the evolutionary steps that
    produced it.
        The place to find earlier steps, of course, should be the Precambrian
    rocks that are more than 543 million years old. Darwin wrote that, if his
    theory is true, then the world must have been swarming with the ancestors
    of the Cambrian critters during long ages before them. He expected future
    generations to find them.
        Today, paleontologists still lack viable ancestors for the Cambrian's
    40 or more animal phyla. Most researchers explain this by assuming that
    Precambrian animals were simply too small or too soft to leave a fossil
    record, or that conditions were unfavorable to fossilization.
        But, for the last three years, Chen's discoveries at Precambrian fossil
    sites with Taiwanese biologist ChiaWei Li have magnified this mystery.
    While sifting through the debris of a phosphate mining site, Chen and Li
    eventually discovered the earliest clear fossils of multicellular animals.
    They found sponges and tiny sponge embryos by the thousands but nothing
    resembling the fishlike Haikouella or forerunners of other Cambrian
    creatures, such as trilobites.
        When word of the discovery got out, Chen and Li suddenly found
    themselves in the international spotlight. But when the hoopla was over and
    their discovery established, they wondered what evolutionary problems they
    had actually solved.
        In fact, the pair had failed to find any recognizable body plans
    showing steps along the way toward the complex Cambrian animals, with their
    legs, antennae, eyes and other features.
        What they had actually proved was that phosphate is fully capable of
    preserving whatever animals may have lived there in Precambrian times.
    Because they found sponges and sponge embryos in abundance, researchers are
    no longer so confident that Precambrian animals were too soft or too small
    to be preserved.
        "I think this is a major mystery in paleontology," Chen said. "Before
    the Cambrian, we should see a number of steps differentiation of cells,
    differentiation of tissue, of dorsal and ventral, right and left. But we
    don't have strong evidence for any of these."
        Taiwanese biologist Li was also direct: "No evolution theory can
    explain these kinds of phenomena."
        In Chen's view, his evidence supports a history of life that runs
    opposite to the standard evolutionary tree diagrams, a progression he calls
    topdown evolution.
        In the most published diagram in the history of evolutionary biology,
    Darwin illustrated what became the standard view of how new taxa, or animal
    categories, evolve. Beginning with small variations, evolving animals
    diverge farther from the original ancestor, eventually becoming new
    species, then new genera, new families, and the divergence continues until
    the highest taxa are reached, which are separated from one another by the
    greatest differences.
        But the fossil record shows that story is not true, according to Chen.
    The differences appear dramatically in the early days, instead of coming at
    the top. Chen suggested that biologists need to seek new mechanisms to
    explain these evolutionary leaps.
        Wherever the first chordates came from, Nicholas Holland of Scripps
    agreed that science should now take seriously the possibility that
    evolution can occur in relatively quick jumps.
        That still leaves a great divide between Chen, Li and the Chinese media
    on one side and the mainstream Western view, in which scientists are
    reluctant to admit that the Cambrian explosion poses a difficult challenge.
        But conferences such as the one in Chengjiang may be changing some
    views. One of the symposium organizers, paleontologist David Bottjer of the
    University of Southern California in Los Angeles, said he disagrees with
    the idea of rapid evolution, but he conceded, "The Cambrian Explosion is
    going to tell us something different about evolution, in the sense that
    it's not the same story that we have always been taught."

    paleontologist JunYuan Chen at the site of the Haiko



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