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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