Charles Darwin’s On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (published in 1859) is a seminal work in evolutionary biology of great historical and scientific importance. Darwinian thought, especially regarding evolution, is now commonly accepted as the most powerful theory in biology and the natural history of species—and the system of natural selection that this theory advanced has been applied (and misappropriated) in many other fields.

Darwin released six updated editions of On the Origin of Species during his lifetime but always considered it merely the popularized “abstract” of a longer work, which he never completed: Natural Selection, a more detailed, scientific account of the basic concepts he presented in On the Origin of Species (which he worried lacked adequate scientific evidence). He initially abandoned the larger project because a colleague, Alfred Russell Wallace, independently (but concurrent) developed natural selection theory. Wallace sent Darwin a draft of his research on the subject in March 1958, prompting Darwin to focus more intently on writing On the Origin of Species, which he completed the following year. However, in 1868, he released part of the longer work, which was published under the title The Variation of Animals and Plants Under Domestication.

On the Origin of Species presents natural selection theory as a framework for understanding and explaining varieties and species and their generation from common parentage over millennia. This theory posits that organisms with random but beneficial mutations succeed in competing for existence in their environment and propagate offspring that exhibit the same modification and similarly benefit. This process persists through generations, and the accumulation of trait differences over time forms new species. Darwin approaches his development of this theory systematically, applying it to myriad problematic issues in natural history, breeding, biology, geology, and paleontology.

During Darwin’s lifetime, On the Origin of Species was extremely controversial. Although it’s now widely considered the cornerstone of evolutionary biology and the scientific community generally agrees with its basic premises, the theory is still divisive and often misunderstood. In Darwin’s day, the prevailing paradigm for explaining the origin of species—which the research of Darwin and other proponents of natural selection theory eventually dethroned in scientific circles—was independent creation theory. Often backed by metaphysical and religious assumptions diametrically opposing Darwinian evolution, this view continued to hold sway in some populations throughout the 20th century and still does today, though its relevance is waning. Although many others in Darwin’s day advocated natural selection, On the Origin of Species remained the central text on the theory.

This study guide references the Everyman’s Library edition, titled The Origin of Species, which reprints the first edition and begins on page 519 of the volume, after the full text of The Voyage of the Beagle.

Content Warning: The source text uses outdated, offensive language when discussing non-Western cultures, Indigenous populations, and Black Africans.

Summary

On the Origin of Species contains 14 chapters, most of which are devoted to the application of natural selection theory to the sciences. Darwin begins by briefly outlining historical progress toward the theory, noting scientific advancements and significant publications. The short introduction acknowledges his debt to others, including Thomas Malthus, states that the purpose of his work is to gain insight into means of species modification and coadaptation, and notes that the book is merely an abstract of a much longer work.

Chapter 1, “Variation Under Domestication,” attempts to explain the causes of species variability in domesticated breeding environments, noting that breeders make modifications for their own good, not for the organism benefit, and that “the conditions of life” (570) are of utmost importance in determining the causes of variability. Chapter 2, “Variation Under Nature,” extends the inquiry to the natural world, which becomes the central focus throughout the rest of the book. Much of this chapter concerns the distinction between species and varieties, a difference that Darwin deems ultimately arbitrary.

Chapter 3, “The Struggle for Existence,” focuses on the complex interconnected competition among species and between members of the same species. The strenuous conditions of life and stark competition among organisms for scarce resources sets up the book’s fundamental concept. Chapter 4, “Natural Selection,” expands on the previous chapter provides an overview of the central theory, detailing “the preservation of favourable variations and the rejection of injurious variations” (601). Darwin shows how natural selection works via descent from common parentage with modification. This chapter includes the book’s only diagram, which subsequent chapters reference; it simplistically maps a genealogical history of species.

In Chapter 5, “Laws of Variation,” Darwin discusses the hidden mechanisms of natural law that determine natural selection. Darwin emphasizes how little scientists know about these laws. (Human ignorance of natural processes is a common theme in Origin.) Chapter 6, “Difficulties on Theory,” to objections to natural selection theory and responds to them. At the end of this chapter, Darwin acknowledges “Conditions of Existence” as the greatest law directing the form of all organic beings, from which even “Unity of Type” derives.

Chapter 7, “Instinct,” investigates the extremely complex instinctual patterns of behavior like those of the honeybee and ants through the lens of natural selection’s slow processes. Chapter 8, “Hybridism,” navigates the problem of sterility among hybrid species while maintaining the importance of variation and diversity in sex, which relates to a potential objection to natural selection’s validity.

Chapter 9, “On the Imperfection of the Geological Record,” and Chapter 10, “On the Geological Succession of Organic Beings,” focus on the fossil record. Darwin considers it deeply imperfect and limited and therefore argues that any challenge to natural selection based on the fossil record requires thorough examination—but that what little the fossil record does provide supports natural selection theory. Chapters 11 and 12, both on “Geographical Distribution,” acknowledge many strange facts about the geographical distribution of species that may mistakenly lead to belief in independent creation theory. Darwin challenges this view and defends natural selection through insights into the nature of seeds, birds, climatic history, and other aspects of life.

Chapter 13, “Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs,” examines the taxonomic problem of species classification, advocating a principled single-system approach. Darwin notes that classification shouldn’t (and generally doesn’t) rely on the mere resemblance of various species but should instead use genealogical heritage as the fundamental principle of organization. To develop this idea, he discusses morphology, embryology, and the genealogy of rudimentary organs. Chapter 14, “Recapitulation and Conclusion,” summarizes Darwin’s findings and some ramifications. Notably, Darwin admits that his view could entail a single source organism as the ultimate ancestor of all of life. Although he never directly addresses what this means for humans, its implications could certainly incite controversy.