- July 24, 2000
See text of paper below, or download pdf (0.8 Mb)
By Fred Heeren
Before smiling officials escorted an international group of foreign scientists to fossil sites in southern China last summer, they made sure gangs of road-building political prisoners were trucked out of sight. The fossil hunters who caught on to this unpleasant little routine shrugged it off as a problem far from their concerns.
The scientists might have been concerned about their own effort to hide troublesome matters — matters that became more apparent when they settled into a resort for a week-long symposium. Sixty scientists from around the world gathered to deliver papers dealing with the conference’s theme: “The Origins of Animal Body Plans and the Fossil Record.”
Though the Western journals Nature and Science later carried articles of the 530-million-year-old fossil discoveries announced at this conference, they made no mention of the central questions emphasized by the discoverers themselves: Why do virtually all the forty or more major animal groups, called phyla, first appear in the fossil record at the same time? Why don’t we see new anima phyla continuing to evolve after this? Why don’t Chinese paleontologists find many millions of years of evolving ancestors for any of these new-but-advanced-looking animals in the strata below them? And why does the Chinese fossil record show evolution’s subsequent history running opposite to traditional Western evolutionary-tree diagrams?
In the West, the evolution of animal life was a cumulative process, the eventual building up of major changes by innumerable, small steps over hundreds of millions of years. Westerners picture an ever-widening tree of life, growing from a single trunk at the beginning and achieving maximum diversity today at the top.
In China, however, the real work of evolution looks more like a one-time event, the greatest evolutionary changes occurring right at the start of the Cambrian period. Chinese paleontologists interpret their fossil cache as a record of a “macroevolutionary” event that took place 543 to 535 million years ago. Within that unique window of opportunity, something special happened, something involving a coordinated influx of incredibly complex genetic information — something that demands “harmony”, as Chinese paleontologists put it, rather than chance and competition.
Chinese evolutionary theory rarely is discussed in English-language academic journals, even though China is the place Western scientists must go to learn about the origins of animal life on Earth. China contains the only fossils in the world that are dated near the start of the Cambrian period, when complex animal groups first exploded onto the scene. International groups make regular pilgrimages to Yunnan province and other paleontological hot spots.
Westerners have had several decades to get used to the idea of “quick-time” evolution and bushlike, instead of treelike, evolutionary diagrams — mostly through the writings of Harvard paleontologist Stephen Jay Gould. Perhaps the best-known paleontologist in the West, he remains the most controversial, and his work receives short shrift in undergraduate textbooks.
Recognizing the lack of fossil evidence for expected transitions between major animal groups, Gould and his colleague Niles Eldredge (of the American Museum of Natural History) promoted a concept they called “punctuated equilibria. ” According to “punk eek,” the fossil record of each animal is characterized by long periods of “equilibrium” where nothing much happens, but this tranquil state is occasionally “punctuated” by relatively quick jumps involving massive changes in the animal. Gould stresses the role of “contingency,” or chance happenings, in provoking these major changes. Rerun the tape of life, he says, and vertebrates, let alone humans, might never appear.
In his 1989 book, Wonderful Life, Gould praised Canada’s Burgess Shale fossils —another key group of Cambrian fossils discovered in Canada — for the “exquisite detail” of their preservation, providing scientists with insight into a crucial period. From his study of these fossils, Gould concluded that no gradual steps possibly could connect pre-Cambrian fungus with the Cambrian animals. He called paleontologists’ efforts to make such connections “fanciful at best.”
But the Chengjiang fossils, all Westerners agree, are fare more exquisitely preserved — and 15 billion years closer to the beginning of the explosion of animal body plans. Indeed, the chance to engage Chinese paleontologist Jun-Yuan Chen is one of the prime motivations for Westerners to travel east. Chen has co-authored half of all papers on the Chengjiang animals, and he recently and he recently discovered Homo sapiens’ earliest traceable ancestor, a small fish-like animal called Haikouella. (While other paleontologists have claimed to have found Cambrian chordates, Chen assembled more than 300 specimens of as Haikouella before announcing this discovery.) Haikouella had a full complement of eyes, a rain, a heart, an esophagus, intestines and so on — appearing so sophisticated that some are classifying the animal as a vertebrate. As a result of Chen’s work, paleontologists now include our own chordate phylum with those that appeared in the early Cambrian.
“Some of these specimens are absolutely gorgeous,” says primitive chordate specialist Nicholas Holland of San Diego’s Scripps Institution of Oceanography, who worries about a problem this discovery raises: “Where are Haikouella’s ancestors? The sixty-four dollar question is, What is this hooked to? That nobody knows.”
Three years ago, the search for ancestors to the Cambrian animals took Chen and Taiwanese biologist Chia-Wei Li to a Precambrian mining site called Weng’an. Knowing that the Precambrian rock there had preserved seaweed, they dreamed of finding developing arthropods — or fossils showing steps leading to any of the 40 or more diverse Cambrian animal groups. At a minimum they hoped to find animals with bilateral symmetry, the most basic characteristic of Cambrian animals (and most animals today). A bilateral animal is one with a top and a bottom, with left and right sides that are nearly identical.
Soon after they began digging, Chen and Li found sponges and tiny sponge embryos. The West publicized the event on network television and the front pages of major newspapers as a great stride in finding the long-sought Precambrian animals. But Chen and Li were disappointed not to have found any bilaterians; they hadn’t found a truly viable ancestor for any of the new animals appearing in the Cambrian explosion.
Moreover, by finding sponges and their microscopically tiny embryos in the Precambrian, they inadvertently rebutted Westerner wisdom. Charles Darwin himself had said that in order for his theory to work, the ancestors of the Cambrian animals must have been evolving for long ages prior to their Cambrian appearance. The reason scientists still haven’t found them, according to Westerners, is that the ancestors must have been too small or too soft, or the conditions for fossilization too poor. But Chen and Li’s discovery had actually demonstrated that small and soft animals were preserved in Chinese Precambrian strata.
“The 580-million-year-old phosphorous rock has good potential to preserve animals, if they exist,” Chen reported to the conferees. “I think this is a major mystery in paleontology, because we didn’t find hard evidence to show that this large number of Cambrian phyla was existing earlier. For me, natural selection is not enough to explain the number of evolution novelties.” More recent evidence for a possible bilaterian animal near the Cambrian/Pre-Cambrian boundary doesn’t solve the problem. Li was also direct: “Evolution should be built on gradual change: mutation plus mutation creating the species, and then the genera and then the family—so how can these animals appear suddenly?”
Western scientists would have none of it. “It doesn’t matter if you find it or not!” declared German biologist Dieter Walossek, rallying his Western colleagues around him. “It’s there! It’s by law! All of the major taxa should have been there in the Precambrian, whether proved or not!”
Valuing theory over data is giving Western science a bad name in the East. During the same week that Westerners read reports in Science and Nature that stressed the Darwinian lessons to be learned from Chen’s discovery of the earliest chordate, the Communist Party’s Guang Ming Daily gave the Chinese people a different story. “Evolution is facing an extremely harsh challenge,” wrote Chinese reporters in an article, “Darwinism — Science or Religion?” Using adjectives such as “dogmatic” and “authoritative” to describe America’s neo-Darwinism, the paper suggested that the theory had taken a wrong turn somewhere in the West. : “In the beginning, evolution was advanced as a scientific hypothesis; one that should be under serious scrutiny from all angles.” The article concluded that, because of the need to contend with creationists, scientists became hypersensitive to any dissent from their “immature science,” and “evolution eventually changed into a religion.”
Today, as a result of Chinese paleontology, biologists must choose between classic Darwinism and “saltation,” the idea of evolution in quick jumps, says biologist Holland. Chinese gossil discoveries have wrought havoc upon his once-tidy tree of life: “You just hardly know what order to put the material in now. I mean, you might as well just present the phyla alphabetically. It’s come to that.”
In China, the Cambrian mystery has recently inspired the building of large new government-sponsored research centers devoted to its investigation. At the heart of their research lies a declaration anathema in the West: a proclamation of the mystery of animal origins on Earth. Rather than “survival of the fittest,” Chen believes scientists should focus on why life kept evolving beyond the fittest. Microbacteria are the most successful forms of life, Chen noted, since they make up most of the Earth’s bio-mass and have survived while all other forms have a way of going extinct. Complex life is less capable of making adaptations. 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.”
At the conference, Chinese scientists encouraged the investigation of a variety of new hypotheses to explain the Cambrian explosion: hydrothermal eruptions, sudden seafloor changes, even intelligent design. This last was too much for one American paleontologist, who stood up and shouted, “This is not a scientific conference!”
Such a tactic, say critics, is the West’s ultimate tool for keeping Chinese scientists at bay: Define all dissent from neo-Darwinism as outside the realm of science.
Ironically, Communist China is famed as a repressive society; the West is supposed to promote the free dissemination of information. Indeed, the American president of the National Academy of Sciences, Bruce Alberts, recently compared science to democracy, in that both accommodate, and are strengthened by, dissent.
For now, however, data contrary to classical neo-Darwinian ideas are as closely guarded as nuclear secrets. Just how powerful is Chen’s “mystery of life”? And why would anyone want to keep neo-Darwinism’s shortcomings a secret? Westerners attending paleontology conferences in the East prefer to steer the discussion away form such questions.
* * *