On the Origin of Species

This is the first of two chapters on geology and the limitations of the fossil record. Here Darwin addresses a potential problem for his theory: the lack of a plethora of transitional varieties between mutable species. He already dispelled the idea that species should live side-by-side with their advanced descendants in the modern world. To find evidence of transitional links, he turns to the geological record. The only problem is that the record is extremely imperfect: “Geology assuredly does not reveal any such finely graduated organic chain” (754). Darwin doesn’t think that this is because no such changes occurred but rather because the geological record is limited:

I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines (777).

Darwin expresses his admiration for Charles Lyell’s Principles of Geology and emphasizes the importance of the long timespans inherent in Lyell’s conception of geological change—that is, the world is extremely old. This impressed on Darwin the “infinite number of generations (of organisms), which the mind cannot grasp” (759). In contrast, he reiterates the serious limitations of the records in natural history museums.

For many reasons (including the migratory habits of marine species, the nature of various geological processes, and the timespan between geological formations) geologists are unlikely to find the gradations of transitional species linking descendants to their ancestors. Darwin notes that we tend to overestimate the value of the current geological record in providing the truth of the history of species. In reality, we haven’t even begun to explore most of our planet’s geological record.

Darwin admits that all the great geologists of his time believe in the immutability of species and writes that he feels “rash” to disagree with so many luminaries. Despite the limitations of the fossil record, however, Darwin holds that the little information it does provide supports natural selection theory, which leads into the next chapter.

In this chapter, Darwin’s goal is not to prove the incontrovertible, deductive validity of natural selection theory but rather to show that it accounts for the nature of the fossil record better than its competitor, independent creation theory. He notes that organisms that have undergone more evolutionary steps—that is, are “higher” in the natural order—also undergo more rapid natural selection. In addition, he notes that good reason supports the view that once a species goes extinct it never reappears. Both these interpretations of the fossil record support natural selection over independent creation. Darwin notes his “astonishment” at the fossils of extinct species and the strong correlation between the extinction (or rarity) of species and the generation of new species.

Darwin writes that “Scarcely any paleontological discovery is more striking than the fact that the forms of life change almost simultaneously throughout the world” (786). For Darwin, this is a very strange fact, and his theory must account for it. He attempts to explain it via a “process of diffusion” (788) of successful species migrating throughout the world and outcompeting others in their natural environment. When this happens, the older forms may lose in the struggle for existence and quickly go extinct. He writes at the end of the chapter:

We can understand how the spreading of the dominant forms of life, which are those that oftenest vary, will in the long run tend to people the world with allied, but modified, descendants; and these will generally succeed in taking the places of those groups of species which are their inferiors in the struggle for existence (802).

He notes that this is happening with invasive species from Great Britain outstripping the native species of New Zealand.

Darwin refers to his diagram in Chapter 4 to show how the affinities between living and extinct species are genealogically evident. He notes that no reason exists to assume that all forms of a species persisted for equal lengths of time—and that despite the long gaps in the geological record that preclude evidence of innumerable transitional forms, strong affinities exist among species on either side of these intervals, which is a result that natural selection theorists would predict: “We find, in short, such evidence of the slow and scarcely sensible mutation of specific forms, as we have a just right to expect to find” (796).

The author holds that in one sense, we can consider present lifeforms improvements over former lifeforms: They hold some advantage in the struggle for life that the previous lifeforms didn’t have, so they persisted when the extinct varieties/species didn’t. He reiterates his view that descent with modification can properly interpret the available fossil record. In addition, he notes that all the forms of life throughout history are interconnected and form “one grand system” (802), one of his theory’s most important implications and a point he returns to in the book’s penultimate and concluding chapters.