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“Darwin’s Dilemma”: Was the Cambrian Explosion Too Fast For Evolution?

A recent paper in Current Biology1 offers some important insights into a question creationists have long raised about the Cambrian explosion, the grand diversification of animals that occurred between about 530 to 520 Ma (millions of years ago). To wit: Was the geologically fast diversification during the Cambrian too fast to be explained by normal evolutionary processes? Does the Cambrian explosion threaten the theory of evolution? To these questions researchers at the University of Adelaide offer a definitive answer: “No.”

Authors Michael Lee, Julien Soubrier, and Gregory D. Edgecombe conclude that despite fast rates of evolution during the Cambrian, “The fastest inferred rates are still consistent with evolution by natural selection and with data from living organisms, potentially resolving ‘Darwin’s dilemma.’”

The researchers examined arthropod lineages, a logical choice given the dominance of arthropods from the Cambrian to the present. (Over 80% of known animal species are arthropods.) By calibrating genomic and phenotypic data with the bountiful arthropod fossil record, Lee et al. determined that the Cambrian rates of evolution were within the boundaries of normal evolutionary processes and the fossil timeline. They concluded that:

...observed rates of molecular evolution could be reconciled with divergences between metazoan phyla as recent as 586 Ma, which (although still pre-dating the Cambrian) is now broadly congruent with recent discoveries of the earliest metazoans.

This research will bring little cheer to contemporary creationists who, following a long and storied tradition, misuse the Cambrian explosion to attack evolution. Their most common line is that the leap of evolution during the Cambrian involved too many changes too quickly, that the Cambrian therefore represents a gap in the fossil record best filled by a supernatural explanation. For example, Henry Morris, the founder of the Institute for Creation Research, wrote in his 1974 book Scientific Creationism:

There is obviously a tremendous gap between one-celled microorganisms and the high complexity and variety of the many invertebrate phyla of the Cambrian. If the former evolved into the latter, it seems impossible that no transitional forms between any of them would ever be preserved or found. A much more likely explanation for these gaps is that they represent permanent gaps between created kinds. Each organism has its own structure, specifically designed for its own purpose, not accidentally evolved by random processes.

Following a string of legal defeats for the openly religious brand of creationism espoused by Morris, creationists used this concept of “specifically designed” organisms as a component of intelligent design creationism (IDC). IDC became a safe front for creationists to espouse scientific terminology while repeating religiously-motivated attacks on evolution.

Creationist rhetoric has changed, but their indignation toward the Cambrian explosion is the same. Phillip Johnson, one of the founders of IDC, wrote in his 1991 book Darwin on Trial:

The single greatest problem which the fossil record poses for Darwinism is the ‘Cambrian Explosion’ of around 600 million years ago. Nearly all the animal phyla appear in the rocks of this period, without a trace of the evolutionary ancestors that Darwinists require.

Morris and Johnson are both wrong about the science, of course, but that hasn’t stopped their flimsy claims from being endlessly reiterated.

Why are creationists so obsessed with this aspect of paleontology, and not, say, the fascinating fossil record of sloths? What special appeal does the Cambrian explosion have for them?

In the “sudden appearance” of organisms during the geologically brief Cambrian explosion, creationists imagine tangible evidence for the supernatural creation of animal “kinds.” To their eyes, these rocks record the moment of creation when Yahweh declared: “Let the land produce living creatures according to their kinds.” They point to Precambrian rocks with their lack of fossilized hard parts, then point to Cambrian layers with their copious fossils and say, “See! Right there: creation.” The story is not so simple, of course; we now know a lot more about life in the period before the Cambrian. The ancient lineages that eventually diversified extend far back in time, a long fuse leading to the eventual explosion.

While the rapid evolution during the Cambrian is described as geologically brief, it is important to define what that means. On human timescales, the shortest estimation for the length of the Cambrian explosion, about 10 million years, is incomprehensibly long. Moreover, the tiny Cambrian arthropods likely had much faster maturations and much shorter lifespans than humans. Our anthropocentric perception of the flow of time, in which a family might have only three or four generations per century, is very different from the number of generations Cambrian critters produced. Ten million years provides plentiful time, as Lee et al. showed. Yet creationists insist that there was not enough time for such biological complexity to arise, without ever defining why that time frame is insufficient.

Creationists will no doubt continue to pontificate about the Cambrian explosion. They create among their followers the illusion that they are remedying some deficiency in science, when in fact they contribute nothing to scientific discourse or peer-reviewed research. When actual scientific research, such as Lee et al., contradicts their unique interpretations, this gives them no pause. Their Cambrian dilemma is not about rates of evolution, but about how to hijack real science in the service of dogma.

 

1 Lee et al., Rates of Phenotypic and Genomic Evolution during the Cambrian Explosion, Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2013.07.055