Evolution's Evolution
"That evolution itself evolved is a new insight."J. William Schopf
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In his 1859 epic, On the Origin of Species, it was Charles Darwin himself who proffered the biggest challenge to the validity of his theory of evolution. Fossil records, which formed the basis of much of his evidence, could be traced back only as far as 550 million years - a point at which complex marine-life organisms already existed. "Darwin could not explain the absence of any fossil record prior to these complex organisms, which he knew were far from the origin of life itself," notes Professor of Paleobiology J. William Schopf, director of UCLA's Center for the Study of Evolution and the Origin of Life, who set out to solve the dilemma more than three decades ago. By the time Schopf was a sophomore in college in the early 1960s, numerous scientists had already tried and failed to solve "Darwin's Dilemma." In fact, says Schopf, "it was thought to be unsolvable." But as it turned out, the problem was human, not scientific: The researchers were asking the wrong questions. In his new book, Cradle of Life: The Discovery of Earth's Earliest Fossils (Princeton University Press), Schopf recounts how he and other scientists, after three decades of work, finally solved Darwin's Dilemma and pushed the evidence of life back by some 3 billion years. For most of the first 85 percent of its history, Earth was populated by microbes - something like pond scum. Fossils from these ancient bacteria were here all the time, but scientists, who couldn't detect them with conventional equipment, never really looked for them. Schopf and others bucked conventional wisdom by looking for fossils of microorganisms, and in 1993, Schopf produced evidence of microscopic cellular organisms nearly 3.5 billion years old, opening the floodgates to research that is filling in the holes in how and when life evolved on Earth. "Everyone had expected that early organisms would be smaller, simpler, perhaps less varied, but they were universally thought to have evolved in the same way and at the same pace as later life," Schopf writes. "This turned out not to be true. That evolution itself evolved is a new insight."
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The pivotal point in evolution's own evolution was the advent of sex about 1.1 billion years ago. The first organisms to engage in sexual activity were single-cell floating plankton, which, unlike organisms that reproduced by asexual division, like human body cells, had a pore-like mechanism that permitted the release of sex cells into the environment. Data from the fossil record clearly show that at about that time there appeared many new types of species. Sex increased variation within species, diversity among species and the speed of evolution and genesis of new species - bringing about not only the rise of organisms specially adapted to particular settings but also the first appearance of life-destroying mass extinctions. "The pre-sex world was monotonous, dull, more or less static," Schopf explains. "But every organism born from sexual reproduction contained a genetic mix that never existed before." Schopf's research taught him as much about scientists as it did about evolution: that science is no more perfect than the humans who practice it. To illustrate the point, Schopf devotes two chapters of Cradle of Life to two of science's more renowned miscues. In 1725, respected Swiss physician and naturalist Johann Jacob Scheuchzer discovered the partial skeleton of a large vertebrate animal in limestone - evidence, he said, of a human who'd drowned in Noah's flood. Scheuchzer's work was hailed as irrefutable proof of Biblical truth until it was shown, almost a century later, to be a misidentified huge salamander fossil. Then, in 1996, NASA scientists grabbed worldwide headlines with the announcement that they'd found evidence of life on Mars in a meteorite that had landed in Antarctica 13,000 years ago. That proclamation has been fairly debunked by many, including Schopf who was asked by NASA to assess the evidence a year-and-a-half before the press conference and believed it did not support the scientists' conclusion. "There's this odd impression of what scientists are like that is very far from the reality," says Schopf. "It's important to understand that scientists have the same foibles as anyone else - and the same capability of making mistakes." - Gary Taubes |
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