This chapter is largely about the problem of the Cambrian Explosion – the sudden appearance of complex animals in the fossil record with no apparent transitional forms, and especially focuses on paleontologist Louis Agassiz of Harvard, a contemporary of Darwin who thought that the “problem of the missing fossils” was fatal to Darwin’s proposals.
But it starts off by giving Darwin credit – everyone knew that artificial or human selection could gradually change the features of an animal (the selective breeding of woolier sheep for example). Couldn’t nature do the same thing (perhaps a series of cold winters would also select for woolier sheep, say)?
This was Darwin’s great insight. Nature – in the form of environmental changes or other factors – could have the same effect on a population of organisms as the intentional decisions of an intelligent agent.
But there was the problem of the Cambrian Explosion, known also to Darwin. Darwin is quoted as saying,
The difficult of understanding the absence of vast piles of fossiliferous strata, which on my theory were no doubt accumulated before the Silurian epoch, is very great… I allude to the manner in which numbers of species of the same group suddenly appear in the lowest known fossiliferous rocks.
(“Silurian” and “Cambrian” are synonyms.) This was the great problem – the species appear suddenly with no ancestral transition forms evident. I was especially struck by the author’s comment that the fossil record is so discontinuous that in fact that is why we identify and talk about different layers in the first place. The whole record (not just in the Cambrian period) is not one of continual development but one of discontinuity.
…the sudden appearance of the Cambrian animals was merely the most outstanding instance of a pattern of discontinuity that extends throughout the geological column.
But maybe we don’t see transitional forms because the species underwent large changes all at once? Doesn’t really happen – Darwin himself conceded that major changes in the form of an individual animal, what would later be called “macromutations” by biologists, inevitably kill the organisms. Only tiny changes can be passed on, and so we should see a very slow evolution in forms.
So where is the fossil record of this evolution? Darwin, apparently quite respectful toward objections to his theory, proposed possible solutions – the precursor animals either hadn’t fossilized or just hadn’t been found yet. Quoting Darwin,
I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect.
Paleontologist Agassiz and others never really accepted this solution which is, after all, an argument from silence – the absence of fossils is not seen as “evidence against Darwinism” but simply “unfortunately missing evidence for Darwinism”.
Aside from that, the end of the chapter looks more closely at Agassiz… and makes some interesting comments on the nature of science in the process. Agassiz himself lived at a time when science was transitioning into what many would say is now the ruling paradigm of “methodological naturalism”, by which the possibility of any kind of divine intervention in the world is automatically disqualified at least from scientific investigation. And indeed, it is sometimes claimed that Agassiz was just trying to cling to the older paradigm in which living forms expressed divine ideals, and that’s really why he disliked Darwin’s ideas. But I thought a couple of comments made by the author about Agassiz would well-describe many scientists today,
Since he regarded material forces, and the laws of nature that described them, as the products of an underlying design plan, he saw any creative work they did as deriving ultimately from a creator… He thought a skillful cosmic architect could work through secondary natural causes every bit as effectively as through direct acts of agency.
A nice comment that would describe many Christians in science today I think, and not one that sounds like the description of a man who would reject Darwin’s ideas for religious reasons.
The chapter ends by suggesting we will further consider the problem of the missing fossils of transition species. See you soon.