The Origin of Species · Chapter
Fertility of Varieties When Crossed, and of Their Mongrel Offspring, Not Universal explained
Darwin challenges the argument that fertility between varieties proves a fundamental distinction from species, showing that sterility can occur in varieties and that domestication tends to eliminate sterility.
What happens
Darwin challenges the argument that fertility between varieties proves a fundamental distinction from species, showing that sterility can occur in varieties and that domestication tends to eliminate sterility. He reviews experimental evidence from Gärtner, Kölreuter, and others to demonstrate that fertility is not an infallible criterion for species status.
Themes in this chapter
Variation and Inheritance
Examines how reproductive fertility varies among varieties and species, challenging fixed inheritance patterns.
Domestication and Artificial Selection
Discusses how domestication alters reproductive systems, often eliminating sterility between varieties.
Natural Selection and the Struggle for Existence
Links sterility in natural varieties to prolonged exposure to uniform conditions and competition.
Characters to notice
- Charles Darwin
Author presenting the argument that fertility does not distinguish varieties from species.
- Gärtner
Conducted experiments on maize and Verbascum showing sterility between varieties.
- Kölreuter
Demonstrated that one tobacco variety produced less sterile hybrids when crossed with a distinct species.
- M. Naudin
Confirmed that certain gourd varieties are ranked as varieties despite crossing difficulties.
- Pallas
Proposed the doctrine that domestication eliminates sterility between species.
Key passages
“the infertility of varieties in a state of nature, for a supposed variety, if proved to be infertile in any degree, would almost universally be ranked as a species”
If a natural variety shows any sterility, naturalists immediately classify it as a separate species.
Highlights the circular reasoning in using sterility to define species.
“The general sterility of crossed species may safely be looked at, not as a special acquirement or endowment, but as incidental on changes of an unknown nature in their sexual elements.”
Sterility between species is not an evolved adaptation but a side effect of unknown changes in reproductive systems.
Darwin's key argument that sterility is incidental, not a designed barrier.
“the Pallasian doctrine of the elimination of sterility through long-continued domestication be admitted, and it can hardly be rejected”
Pallas's idea that domestication removes sterility is almost certainly correct.
Darwin supports Pallas's view to explain why domestic varieties are often fully fertile.