The Origin of Species · Chapter
Causes of Variability explained
Darwin explores the causes of variability in domesticated plants and animals, arguing that changed conditions of life, especially over multiple generations, induce variation.
What happens
Darwin explores the causes of variability in domesticated plants and animals, arguing that changed conditions of life, especially over multiple generations, induce variation. He distinguishes between direct effects on the organism and indirect effects through the reproductive system, emphasizing the primacy of the organism's nature over external conditions. He also discusses definite versus indefinite variability and notes that bud variations can occur without sexual reproduction.
Themes in this chapter
Variation and Inheritance
Central theme: Darwin analyzes how changed conditions cause variation, both definite and indefinite, and discusses the role of the reproductive system.
Domestication and Artificial Selection
Key context: The chapter focuses on variability in domesticated plants and animals, linking it to conditions of life under human care.
Characters to notice
- Charles Darwin
Author and primary narrator, presenting his observations and conclusions on variability.
- Professor Weismann
Cited for his insistence on the two factors of variation: the nature of the organism and the nature of the conditions.
- Kölreuter
Mentioned for his observation of similarity between variability from crossing species and that from new conditions.
- Andrew Knight
Referenced for the view that variability may be partly connected with excess of food.
Key passages
“When we compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature.”
Individuals of the same cultivated variety tend to show more variation among themselves than individuals of a wild species or variety do.
Darwin introduces the observation that domesticated forms are more variable than wild ones.
“The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform.”
The nature of the organism is more influential than the environment, since similar variations can occur under different conditions and different variations under similar conditions.
Darwin emphasizes the primacy of the organism's internal nature over external conditions in causing variation.
“Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even when the male and female unite.”
Taming animals is easy, but getting them to reproduce in captivity is often very difficult, even if mating occurs.
Darwin highlights the sensitivity of the reproductive system to changed conditions.