This is one of the most underrated apologetics arguments. The Cambrian explosion is admitted by mainstream paleontologists; the interpretation is where it gets interesting.
The facts (uncontroversial)
- The Cambrian period began about 538.8 million years ago (International Commission on Stratigraphy). Over the following twenty-plus million years, most animal phyla with good fossil records make their first appearance.
- "Phyla" are top-level body plans — vertebrates, mollusks, arthropods, etc. These are not species; they are the broadest categories of animal architecture.
- How long it took depends on what is measured. From the base of the Cambrian (538.8 million years ago) to the Chengjiang fossils (no older than about 518 million years) is more than twenty million years, and the study that dated Chengjiang calls the explosion "a protracted process (>22 myr)." Within that span many groups first appear in a shorter pulse: a 1993 study by Samuel Bowring and colleagues put two key early-Cambrian stages at "only 5 to 10 million years" on the dating then used, and a 2011 review by Douglas Erwin and colleagues says diverse bilaterian groups "emerged apparently within a few million years."
- Before the Cambrian: the Ediacaran biota, the first large, complex organisms in the fossil record, some of them now confirmed as animals (Dickinsonia), along with simple horizontal burrows and early mineralized tubes such as Cloudina. After: a wide range of animal body plans, many of them belonging to "stem groups" that have some, but not all, of the features of living groups.
Darwin's own concern
Darwin himself, in Origin of Species (chapter 9), worried about exactly this pattern: "The case at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained." He hoped future fossil discoveries would fill the gap.
The expected Darwinian pattern
Gradual divergence over very long times — simple ancestors slowly accumulating differences. The fossil record should show many intermediates between simple Precambrian life and complex Cambrian phyla.
The actual pattern
Many phyla appear within a geologically short time, and clear Precambrian ancestors for most of them have not been found. The Burgess Shale (1909, Canada) and the Chengjiang fauna (1984, China) preserve detailed soft-bodied fossils. Many of these animals belong to "stem groups" with some, but not all, of the features of living groups: the Royal Ontario Museum's example is Opabinia, which has a long, flexible feeding proboscis ending in a claw and other arthropod-like features, and is placed in the stem lineage of the arthropods rather than among living groups. Specialists read such animals as intermediates; design theorists reply that they do not close the gap before the Cambrian.
The information problem (Stephen Meyer's argument)
In Darwin's Doubt (2013), Meyer argues that building a new animal body plan requires massive amounts of new genetic information — new genes, new regulatory networks, new developmental pathways. On his reading, the Cambrian explosion requires this information to appear in a geologically brief window. Where did it come from?
Meyer and his colleagues argue that random mutation and natural selection are too slow and too undirected to produce that much new information in the time available. Most evolutionary biologists disagree (see the responses below).
Mainstream responses
- Soft-bodied ancestors didn't fossilize. Possible — but other soft-bodied animals (worms, jellyfish) did fossilize from this period. Why not these supposed ancestors?
- Genetic regulatory networks were already in place. Maybe — but where did they come from? This pushes the problem back, not away.
- Punctuated equilibrium (Gould and Eldredge) — evolution proceeds in bursts. This acknowledges the pattern but doesn't explain the mechanism for such rapid information increase.
What the paleontologists say
Simon Conway Morris (one of the leading Cambrian researchers, and a Christian) has written extensively on the pattern of sudden body-plan appearance.
The Orthodox lens
The Fathers were not committed to any specific mechanism of creation. St. Basil's Hexaemeron (Homily 5) says that God's command to the earth became "as a natural and permanent law for it," so that "this first command teaches nature what she has to do in the course of ages" (though Basil himself assumed that living kinds were fixed). A Cambrian "explosion" is consistent with — even suggestive of — divine action shaping natural history at key moments.
An important caveat
The Cambrian explosion does not by itself prove Christianity. Design theorists such as Meyer argue that it poses challenges to Darwin's mechanism that mainstream evolutionary biology has not overcome, and that the best explanation for the appearance of integrated, information-rich biological systems is a Mind acting in nature's history. Specialist reviewers disagree, and the question remains debated.
A pastoral word
If you have been told that evolution is settled science with no loose ends, the Cambrian explosion is one of many places where the actual fossil record is more complicated than the textbook summary. You don't need to fear the evidence. Christians read it in more than one way: design theorists see the marks of design in it, while other Christians, including some of the scientists who study it, see God at work through the processes of nature themselves. Either way, "His invisible attributes are clearly seen, being understood by the things that are made" (Romans 1:20).