The Origin of Species · Chapter
Correlated Variation explained
Darwin explores the phenomenon of correlated variation, where changes in one part of an organism lead to modifications in other parts during growth and development.
What happens
Darwin explores the phenomenon of correlated variation, where changes in one part of an organism lead to modifications in other parts during growth and development. He discusses how homologous parts tend to vary together, how hard parts affect soft parts, and gives examples such as the relation between hair and teeth in mammals, and the differences between outer and inner flowers in Compositae and Umbelliferae. He argues that many structural modifications may arise from laws of variation and correlation without being directly beneficial, and cautions against falsely attributing inherited traits to correlation.
Themes in this chapter
Variation and Inheritance
The chapter focuses on how variations in one part can lead to modifications in other parts, and how inheritance can give a false appearance of correlation.
Adaptation and the Utilitarian Doctrine
Darwin argues that many correlated variations may not be directly beneficial, challenging a strictly utilitarian view of natural selection.
Characters to notice
- Mr. Mivart
Cited for noting exceptions to the rule about abnormal dermal covering and teeth in mammals.
- Dr. Hooker
Provided information about Umbelliferae, noting that species with densest heads do not most frequently differ in inner and outer flowers.
- Geoffroy Saint-Hilaire
Remarked on the frequent coexistence of certain malconformations without assignable reason.
- De Candolle
Mentioned for founding main divisions in Umbelliferae on seed shape differences, and for noting that winged seeds are never found in fruits that do not open.
- Sprengel
His idea that ray-florets serve to attract insects is cited as probable.
Key passages
“Correlated Variation I mean by this expression that the whole organisation is so tied together, during its growth and development, that when slight variations in any one part occur and are accumulated through natural selection, other parts become modified.”
By 'correlated variation,' Darwin means that the entire organism is interconnected during growth, so that small changes in one part, when selected, cause changes in other parts.
Defines the central concept of the chapter.
“Hence modifications of structure, viewed by systematists as of high value, may be wholly due to the laws of variation and correlation, without being, as far as we can judge, of the slightest service to the species.”
Structural differences that taxonomists consider important may arise purely from variation and correlation, not from any adaptive benefit to the species.
Highlights Darwin's argument that not all traits are adaptive.