How to Solve the Cambrian Explosion: Turn Up the Evolutionary Speed Dial - Evolution News & Views

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How to Solve the Cambrian Explosion: Turn Up the Evolutionary Speed Dial


Among the scientific papers out there that try to refute Stephen Meyer without naming him, here's one that makes it all so simple: evolution just ran faster in the Cambrian, that's all.

It's amazing how the news media flocked to a new paper in Current Biology by Lee, Soubrier and Edgecombe, "Rates of Phenotypic and Genomic Evolution during the Cambrian Explosion." It's as if they were breathing a collective sigh of relief: now we don't have to deal with Meyer's new book Darwin's Doubt; why? Because the doubt has been replaced with certainty. The paper announces confidently, "The Cambrian explosion (evolution's "big bang") is compatible with Darwinian evolution." (Emphasis added.)

In a nutshell, the paper asserts that evolution ran 4 to 5.5 times faster during the Cambrian than its usual slow-and-gradual speed. To come up with that measure, Lee and Soubrier from Australia and Edgecombe from London's Natural History Museum compared 395 phenotypic characters and 62 genes from living arthropods, "the most diverse phylum in the Cambrian and today." Since evolution ran faster, all the "major phenotypic innovations" were able to "suddenly appear" in a shorter time interval. (They assume that whatever sped up evolution for arthropods also accelerated the other phyla that "appeared" in a geological instant: "This study concerns arthropods, but the results are likely applicable to most of life.")

Like magic, the problem is solved. "The findings, published online today in the journal Current Biology, resolve 'Darwin's dilemma': the sudden appearance of a plethora of modern animal groups in the fossil record during the early Cambrian period," a press release from the University of Adelaide announced proudly, their Associate Professor Michael Lee standing in the limelight. The Cambrian explosion was nothing more than standard evolution running in time-lapse.

A look into the paper reveals damaging admissions, glaring omissions, and lapses in logic. Let's look at these in turn.

Damaging Admissions

The authors admit that the Cambrian explosion was sudden. They know it gave Charles Darwin grave doubts: "Darwin famously considered that the sudden appearance of complex morphologies in the lower Cambrian was at odds with normal evolutionary processes." They also know that subsequent studies concluded the same thing:

Many subsequent workers have reasonably contended that this pulse of diverse fossils is not explicable without either positing a lengthy cryptic Precambrian prelude or invoking "unknown evolutionary mechanisms." Similarly, initial molecular analyses concluded that the extensive molecular divergences between arthropods, echinoderms, and chordates could not be fully reconciled with the abrupt Cambrian fossil record, assuming even the fastest modern rates of molecular evolution.

They also know that critics of Darwinism are waving these facts in their faces: "These legitimate reservations have predictably been exploited by opponents of evolution."

Another fact they acknowledge is the lack of evidence for a long Precambian "fuse" leading up to the explosion. Their own work, in fact, supports the "emerging consensus" that any Precambian lead-up to the explosion had to be short, not only because there's no fossil record of it, but also because it doesn't solve the problem that animals "acquired many novelties simultaneously across the early Cambrian." The Ediacaran fossils, therefore, do not help.

Consequently, they agree that the time of rapid innovation was brief, fitting within 40 million years (Meyer provides evidence it was as short as 5 million years, 1/10 of 1% of Earth's history, p. 72). Although they assume the generous evolutionary estimate of 40 million years, they recognize the period of rapid arthropod divergence is compressible to less than 10 million years in the Lower Cambrian.

They also admit that this period was unique: "evolution during the Cambrian explosion was unusual (compared to the subsequent Phanerozoic) in that fast rates were present across many lineages."

Glaring Omissions

The paper assumes that speeding up natural selection solves all the problems and brings the Cambrian diversification safely back into Darwin's fold. What they fail to acknowledge is that each phylum appears abruptly in the fossil record, with no transitional forms. The first trilobite is all trilobite. The first Anomalocaris is all Anomalocaris. The Cambrian explosion is not just a matter of brevity of time. It's a gap between microbes (or bland multicellular colonies, if one considers the Ediacaran animals) and fully integrated body plans with jointed legs, complex eyes, guts, brains, nervous systems, and a whole new ecology.

Speeding up the evolutionary clock, therefore, doesn't solve the real problem Meyer emphasized in his book: where did the information come from to build all these new body plans? If you doubled or tripled the time interval, it wouldn't change that issue. The absence of transitions and the sudden appearance of complex tissues, organs, and systems cry out for explanation, however one might quibble about the duration of the explosion.

At one point, after declaring that evolution ran 4 to 5.5 times faster than normal, the authors claim that their conclusions are robust, even when compressing the explosion to the briefest interval:

Surprisingly, these fast early rates do not change substantially even if the radiation of arthropods is compressed entirely into the Cambrian (∼542 mega-annum [Ma]) or telescoped into the Cryogenian (∼650 Ma). The fastest inferred rates are still consistent with evolution by natural selection and with data from living organisms, potentially resolving "Darwin's dilemma."

That assertion, however, relies on transitional forms that are not found in the fossil record. They need transitions to show that natural selection, even if running at high speed, built these animals piecemeal by selecting small variations. Even Lee and team would never assert that a microbe divided and a trilobite hatched out.

Let's take them up on compressed rates and see what it means. Suppose you are on MythBusters testing a new model of explosions. A mythmaker alleges that explosions are really slow and gradual, and occur by natural processes of sunlight hitting soil, instead of by someone assembling a bomb. The equipment measures the duration of an explosion at 20 milliseconds. Suppose that the mythmaker then claims that it was really 10 seconds, if you consider the lead-up and the aftermath. Then he boasts that he can even compress that interval by half to 5 seconds, and his natural model of the explosion still holds. Would the MythBusters accept that story? No; they would laugh the guy off the set. The essence of the explosion was its suddenness. It wouldn't matter if you "telescoped" or "compressed" the time around the explosion; the explosion itself was abrupt. In the same way, when you find a whole trilobite in a layer of rock with no precursors, that's the issue! Quibbling about how many million years passed before and after it "suddenly appeared" adds nothing to our understanding.

Lapses in Logic

Lee and team play with the "speed dials" of natural selection, assuming that evolution can run up to 5.5 times faster than normal and still fit within a Darwinian paradigm. They've already abandoned the "slow Precambian fuse" explanation, so the only other option is "unknown evolutionary mechanisms" that some have suggested. By asserting that ordinary evolutionary mechanisms, running faster, are sufficient, they feel they have solved "Darwin's dilemma" and answered the "opponents of evolution" who "predictably exploit" the "legitimate reservations" that the Cambrian explosion presents.

They're answering the wrong question. It's not a question of slow evolution vs. fast evolution. It's not a question of evolution by unknown mechanisms vs. known mechanisms. Evolution itself is the issue! The Cambrian explosion poses the question of Darwinian evolution vs. intelligent design, because the sudden appearance of some two dozen distinct body plans without precursors challenges any naturalistic explanation, no matter how fast it runs.

In essence, Lee and team are simply saying, "They evolved because they evolved faster." That's not the challenge the fossil record poses. It's a circular answer that assumes evolution to argue for evolution. Here's another example: "Clades characterized by major phenotypic innovations often exhibit higher rates of evolution initially...."

Meyer's books pose fundamental challenges to evolution and other naturalistic explanations, not just "exploiting" the "legitimate reservations" about the rate of evolution but about evolution itself as a scientific explanation. He's not just poking holes in evolutionary theory. He's making a positive case for design: whenever you find information-rich systems with integrated parts contributing to function, whether it be a computer or a trilobite, we know from our uniform experience that intelligence played a role in its origin. They need to stop attacking straw men and face these issues.

Lee and team also commit a common evolutionary fallacy we might call the "opportunity knocks" theory of evolution. They assume that natural selection, filled with creative power and desire to invent endless forms most beautiful, will rush to fill new environmental opportunities. Here's how they dress this idea up in jargon: they speak of "ecological opportunism coupled with a more complex fitness landscape, which might have unleashed latent evolutionary capabilities" -- a complicated way of saying, "vacant space brings entrepreneurs." While that may work in economics with intelligent human beings, microbes are under no obligation to become trilobites, just because of "ecological opportunism." This talk of "latent evolutionary capabilities" personifies the simple organisms before the Cambrian explosion, making them out to be contestants in an invention challenge, chomping at the bit to innovate.

Media Hype

Of the papers we've examined that try to answer the Cambrian explosion, this one be Lee et al. must surely rank as one of the silliest. They dodge the important issues. They argue in a circle, using evolutionary assumptions to defend evolution. They employ ad hoc reasoning to avoid falsification of evolutionary theory. They fight straw men. Despite the jargon, their conclusions are vapid, evasive, and illogical.

Yet the hype-to-data ratio has been off the charts: the media trumpeted this as the answer to all the critics, the scientific "findings" to finally rescue Darwin from his dilemma. At Live Science, in an article echoed around the Internet, Tia Ghose wrote, "Lightning-Fast Evolution Clocked During Cambrian Explosion" as if Lee was holding a stopwatch.

A crustacean with 3,000 lenses in its eyes, 6-foot-long shrimplike creatures and organisms that looked like tulips emerged hastily (from an evolutionary perspective) on the scene some 520 million to 540 million years ago. And now scientists have figured out just how quickly evolution was occurring during evolution's "big bang."

Acknowledging that the Cambrian explosion saw the "sudden emergence" of "most of the planet's modern animal groups," including creatures with eyes, antennae, biting jaws, jointed legs and much more, Ghose triumphantly announced that Lee and his colleagues have stood up to those pesky creationists:

Researchers have long debated exactly how animals could have evolved so quickly during the period. Creationists have even used the Cambrian explosion to raise doubts about the theory of evolution, suggesting some divine hand must have played a role....

Why are we not surprised at that red herring?

The team found that the emergence of many sea creatures during the Cambrian explosion could be explained by an accelerated -- but not unrealistic -- evolution by way of natural selection, or the process in which organisms change over time due to changes in heritable physical or behavioral traits.

Giving lead author Michael Lee the pulpit for the benediction, her article ends,

"In this study we've estimated that rates of both morphological and genetic evolution during the Cambrian explosion were five times faster than today -- quite rapid, but perfectly consistent with Darwin's theory of evolution," Lee said.

At least Science Magazine offers a hint of caution in its otherwise gushing praise:

"It's an excellent first step," says Douglas Erwin, a paleontologist at the Smithsonian Institution in Washington, D.C., but the exact rates of evolution in the study might not be reliable. He points out that while the study uses fossil data to determine when a given arthropod branch emerged, it doesn't include the known characteristics of these extinct ancestors in its comparisons of physical traits, which involve only living creatures.

Some of the assumptions the authors make in estimating these emergence dates are also problematic, says Philip Donoghue, a paleobiologist at the University of Bristol in the United Kingdom.

That coverage led to a lot of lively comments from readers, many mocking intelligent design with the usual ad hominems and conflation with creationism, plus some well-meaning but misguided responses misrepresenting ID. Won't one of these people just get a copy of Darwin's Doubt and read it?

On the bright side, the lack of substantive responses to the arguments of Meyer and others provides tacit admission that the case for intelligent design remains robust.