The Cambrian Explosion: Part 1

I wrote most of this blog on the Cambrian Explosion a while back, but its length made me hesitant to post it. I have recently been motivated again to present the evidence. In an effort to keep individual posts of a more readable length I will do so as a multipost blog.

About 540 million years ago, the first fossil universally-recognized members of modern phyla appeared. Over a period of 50 million years almost all phyla have made there first appearances. This period of rapid diversification is called the Cambrian Explosion.

Many creationists including Intelligent Design proponents make the claim that the Cambrian Explosion is an obvious slam-dunk refutation of modern evolutionary theory. The problem, they say is that the evidence says all phyla popped into existence in a manner that supports Special Creation more so than modern evolutionary theory. However, these are the same people that say that the whole fossil record is a big embarrassment to evolutionary theory. I hope I have shown that is not so with my post on macroevolution and actually showing the progression of fossil skulls showing intermediates between chimpanzee-like apes and modern humans.

Again, I hope to show that things are not quite like these creationists would have you believe. While there are aspects of the Cambrian Explosion that present problems for modern evolutionary theory, these problems stem from uncertain knowledge. Potential mechanisms that fall well within the realm of modern evolutionary theory exist no matter which way the ultimate results fall. Furthermore, what we actually DO know about the Cambrian Explosion is VERY DIFFICULT to explain under the umbrella of creationism or Intelligent Design.

Before I go further, I want to head off a potential nitpick. Intelligent Design (ID) has gone out of its way to distance itself from creationism so I might be accused of using a pejoratively linking the two above. However, I think it is absolutely correct to do so with respect to the Cambrian Explosion. The supposed problem is that there isn’t enough time for the diversity of life seen in the Cambrian to have evolved by natural means. If not natural, then what? These lifeforms must have been engineered by some super-designer, they say. That is SPECIAL CREATION. And Special Creation is the hallmark of creationism.

One of the “evidences” that ID proponents stress as to why ID is not creationism, is that ID does not require Special Creation. They often cite Michael Behe’s on-record statements that he accepts that all life came from a common ancestor. I think it is somewhat disingenuous on their part to argue against it on the basis of the Cambrian Explosion, while at the same time using this to distinguish them from creationism.

Now, let’s begin our examination of what the Cambrian Explosion is and compare creationism/ID and modern evolutionary theory as to how it may explain the results. Unfortunately to give one a full picture of the evidence as we know it requires explaining a lot of technical biology. I will do my best to do so in a manner that is understandable to anyone interested in the subject regardless of background.

I think it is very instructive to look at the problem as it was during Darwin’s time and look at the progress that we have made since then. In Darwin’s time geology had already identified the major strata. Fossils first appeared in the Cambrian strata. They were quite diverse and were of pretty complex animals. Some were as large as 3 to 5 feet in length and many included complex organs such as eyes. Geology had estimated the strata to be several hundred million years of age, but no exact dates could be attributed to them.

Soon however, the renowned physicist, Lord Kelvin, performed calculations that cast severe doubt on the geological estimates of the age. Kelvin looked at heat loss from the surface of the earth. He reasoned that if the earth had started off in an entirely molten state, then in a period of NO MORE than 60,000,000 years it would have cooled to what it is now.

The Cambrian strata was by no means the lowest (and therefore oldest) of the strata known. Could life have begun and diversified into such complex creatures in the short amount of time this seemed to imply? To make matters even worse, Lord Kelvin refined his calculations and lowered the estimated age of the earth to 20,000,000 years.

Darwin worried about this quite a bit. He anticipated and eloquently addressed so many criticisms (most still used by creationists to this day) of his theory in his book On the Origin of Species. But for this one, he had to speculate. Darwin was first known in scientific circles as a geologist, so he was suspicious of Kelvin’s calculations but knew of nothing inherently wrong with them. He felt like the problem of intermediate fossils would be solved as more fossils were found and the fossil record was fleshed out.

Interestingly his friend and defender, Thomas Henry Huxley, was not the least bit concerned by Lord Kelvin’s calculations. He thought the evidence was clear that evolution HAD occurred. Thus, to him all the timescale of the age of the earth would tell us was how fast evolution could proceed. He was never a particular fan of the gradualness with which Darwin thought evolution must proceed. He agreed with Darwin, however, that as the fossil record became more apparent the intermediate fossils would appear.

So during Darwin’s day, the Cambrian Explosion might rightfully have been referred to as a problem that might be unexplainable within the Darwinian paradigm. No candidate precursor fossils for the relatively complex forms were known and there were severe doubts about how long natural selection had to work in producing the diversity seen. How has what we have found out since Darwin’s time affected that problem?

In my next post I will detail the resolution of the Lord Kelvin problem and discuss what has since been discovered about the Precambrian fossil record.

Cheers,

Darwin's Beagle