little fish challenges a giant of science
By Fred Heeren
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 530-million-year-old 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,
Jun-Yuan Chen and his colleagues reported dryly that the ancient fish
"will add to the debate on the evolutionary transition from invertebrate
But the new fossils have become nothing less than a
challenge to the theory of evolution in the hands 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 show that
modern life forms burst on the scene suddenly, rather than through any
According to Chen, the conventional forces of evolution
can't account for the speed, the breadth, and one-time nature of "the
Cambrian Explosion," a geological moment more than 500 million years ago
when virtually all the major animal groups first appear in the fossil
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 Haikoulla 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
Taunts from the Communist Party wouldn't carry much
sting, however, if some Western scientists weren't also concerned about
weaknesses in so-called neo-Darwinism, the dominant view of evolution
over the last 50 years.
"Neo-Darwinism 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 neo-Darwinism 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
non-Western 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 geological period known as
the Cambrian. And Chengjiang, in the southern province of Yunnan, contains
the oldest and best preserved Cambrian fossils in the world. Jun-Yuan
Chen has co-authored 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, Haikoulla 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
"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 the 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
According to Chen, the two main forces of evolution
espoused by neo-Darwinism, natural selection ("survival of the the fittest")
and random genetic mutation, cannot account for the sudden emergence of
so many new genetic forms.
"Harmony can be driving force [of evolution], too,"
Chen proposed at the Chenjiang 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.
Biologist had been expecting to see something that
would 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 less-complex ancestor, Chen instead found a
chordate that already displayed many vertebrate characteristics 15 million
And some of the 305 fossil specimens Chen's team has
recovered are so well preserved that paleontologists practically swoon
"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 life 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 Precamrian 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 the 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 Chia-Wei 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 fish-like 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 paleontogy," 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 top-down 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 appearances 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
But conferences such as the one in Chenjiang may be
changing some views. One of the 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."