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Chapter Summary
Evolutionary theory is a testable, unified, and fruitful scientific theory. Material evidence of evolutionary change over time can be found in the fossil record and in the pattern of distribution of a wide variety of living species of organisms.
Before Darwin’s writings were published and popularized in the mid-late 1800s, European thinkers divided living things into natural kinds, each of which was thought to have its own unchanging essence. The Great Chain of Being was understood as God’s creation, naturally harmonious and without gaps, and it inspired Linnaeus’s taxonomy of living organisms.
In the nineteenth century, catastrophism and uniformitarianism undermined the Great Chain of Being. Catastrophism was based on the ideas of Georges Cuvier, who argued that some species had become extinct in massive natural disasters, after which new species were introduced from elsewhere. Uniformitarianism was promoted by geologist Charles Lyell, who argued that the same processes of erosion and uplift that can be observed to change the earth’s surface today had been at work in the past. Uniformitarianism implied that changes in life forms were as gradual and reversible as changes in the earth’s surface.
Lamarck tried to preserve the view of a harmonious Great Chain of Being by claiming that fossil species had not become extinct. Lamarck argued that individual members of a species are all able to transform themselves in the same way when facing the same environmental pressures. Lamarckian transformational evolution has been rejected by contemporary evolutionary researchers. In contrast to Lamarck, Darwin and Wallace concluded that the similarities shared by distinct living species could be explained if all such species had descended from a single parental species that had lived in the past. In addition, Darwin proposed that such “descent with modification” could occur as a result of the straightforward, mechanistic process of natural selection.
Learning Objectives
In this chapter, the student should learn to do the following:
- explain how and why the theory of evolution influenced how people view notions of history and change over time;
- explain the differences between transformational and variational evolution;
- outline how cultural and religious beliefs informed such ideas as essentialism and the Great Chain of Being;
- explain the difference between a genotype and phenotype and why these differences are significant;
- outline the various types of principles behind the different forms of Mendelian inheritance; and
- outline the content of Odling-Smee et al.’s “controversial proposal.”