On the Origin of Species | Study Guide

Charles Darwin

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On the Origin of Species | Chapter 11 : On the Geological Succession of Organic Beings | Summary



In chapter 11 Darwin is mainly concerned with delving further into the "imperfection of the geological record." Claims that the geological record is complete and accurate results in the rejection of the theory of natural selection. Darwin begins with a series of observations to prove his theory. First, species formation is slow. Within the same genera, the rate of change of any one species is independent of any other, and variations are ultimately directed by a variety of "complex contingencies."

Darwin then discusses the process of species extinction, claiming catastrophism had been "generally given up" by contemporary geologists. Instead, the extinction of species is believed to be a process as slow—if not slower—than the process of species formation. In order to explain the way extinction occurs, he describes "unperceived hostile agencies"—the slow replacement of one species with another form with more beneficial adaptations—and factors such as competition.

Darwin then describes how change seems to occur simultaneously throughout the world over long periods of time. He argues this process can be explained by natural selection and the diffusion of species over time across the planet. In this section he also addresses the objection an extinct species can be considered an "intermediate between any two living species." He refers to the diagram presented in Chapter 4, claiming by extending the time span, it is easy to conceptualize natural selection over long periods of time.

Later in the chapter, Darwin offers examples of extinct species that were ancestors to modern species present in the same region. Darwin argues for a "law of the succession of types" to explain the relationship between modern and extinct species in the same region. This pattern can be explained by the theory of natural selection.


Darwin presents a dual message in this chapter. The geological record may be incomplete, but it is also a record of the ancestral connections between extinct and modern species. Darwin hypothesizes the geological record offers evidence to support the theory of natural selection.

Darwin claims catastrophism has been rejected by the majority of geologists and the slow time depth associated with extinctions is explained by the theory of natural selection. Many geologists adhered to the theory of catastrophism, but it was gradually replaced by the theory of uniformitarianism, thanks to the work of James Hutton and Charles Lyell.

Uniformitarianism is the idea the same processes that formed the earth in the distant past remain in effect today. This implied a longer time span for the formation of geological layers and the extinction of species, both of which provide additional support for the theory of natural selection. However, due to the nature of the geological record and the formation of fossils, the record is inherently incomplete. This fact cannot be discounted when formulating theories of biological processes using the geological record.

Darwin notes the periods of worldwide change in species composition are only explained by the theory of natural selection. Similar processes can also explain the resemblance between ancient and modern species in one area. Overall, the incorporation of the theory of uniformitarianism is indispensable to strengthening Darwin's argument for the theory of natural selection. He makes this influence explicit, both by citing Lyell and through the relatively large portion of the work he dedicates to elucidating the connection between biological and geological processes.

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