The Origin of Species · Chapter
V: Laws of Variation explained
Darwin examines the causes and patterns of variation in organisms, arguing that variability is generally related to conditions of life, but that the nature of the organism is more important than the environment.
What happens
Darwin examines the causes and patterns of variation in organisms, arguing that variability is generally related to conditions of life, but that the nature of the organism is more important than the environment. He discusses the effects of use and disuse, the role of natural selection in shaping rudimentary and highly developed organs, and why specific characters are more variable than generic ones.
Themes in this chapter
Variation and Inheritance
Central theme; Darwin explores the causes of variation, including direct and indirect effects of conditions, and the role of use and disuse.
Adaptation and the Utilitarian Doctrine
Discussed in the context of natural selection acting on variations that are of slight use, and the difficulty of separating effects of conditions from selection.
Natural Selection and the Struggle for Existence
Applied to explain the wingless condition of Madeira beetles and the variability of highly developed parts.
Characters to notice
- Charles Darwin
Author and narrator; presents his arguments on the laws of variation.
- Professor Owen
Quoted regarding the anomaly of flightless birds.
- Mr. Wollaston
Cited for observations on wingless beetles in Madeira and the effect of sea air on insect colors.
- Mr. Gould
Referenced for the belief that birds are more brightly colored under clear atmospheres.
- Edward Forbes
Mentioned regarding shell color variation with latitude and depth.
Key passages
“Some authors believe it to be as much the function of the reproductive system to produce individual differences, or slight deviations of structure, as to make the child like its parents.”
Some writers think that the reproductive system's role is not only to produce offspring resembling parents, but also to generate small variations.
Introduces the idea that variation is a normal function of reproduction.
“In all cases there are two factors, the nature of the organism, which is much the most important of the two, and the nature of the conditions.”
Every instance of variation involves two factors: the organism's inherent nature (the more significant one) and the environmental conditions.
Highlights Darwin's emphasis on internal causes over external conditions.
“When a variation is of the slightest use to any being, we cannot tell how much to attribute to the accumulative action of natural selection, and how much to the definite action of the conditions of life.”
When a variation is even slightly beneficial, it is difficult to determine whether it arose from natural selection over generations or from a direct environmental effect.
Acknowledges the challenge of disentangling selection from direct environmental influences.