The Origin of Species · Chapter
Degrees of Sterility explained
Darwin examines the evidence for sterility in species crosses and hybrid offspring, arguing that sterility is not universal but varies in degree and can be influenced by domestication and close interbreeding.
What happens
Darwin examines the evidence for sterility in species crosses and hybrid offspring, arguing that sterility is not universal but varies in degree and can be influenced by domestication and close interbreeding. He critiques the work of Kölreuter and Gärtner, showing that their conclusions often conflict, and presents cases where hybrids are fertile, challenging the notion that sterility is a definitive barrier between species.
Themes in this chapter
Variation and Inheritance
Darwin explores how sterility varies in degree and can be inherited, and how close interbreeding affects fertility in hybrids, linking to broader patterns of inheritance.
Domestication and Artificial Selection
The chapter highlights how domestication can remove sterility, as seen in dogs, cattle, and geese, showing that reproductive barriers are not fixed.
Characters to notice
- Kölreuter
Cited as a conscientious observer who made the rule of sterility universal, but cut the knot by ranking fertile crosses as varieties.
- Gärtner
Another meticulous hybridiser whose experiments on sterility are discussed; Darwin notes his methods may have impaired fertility and that his conclusions sometimes conflict with Kölreuter's.
- Pallas
Propounded the alternative that hybrids reared under domestication became quite fertile, a view Darwin finds probable.
- Mr. Blyth
Provided observations on differences in habits, voice, and constitution between Indian humped and common cattle, supporting their status as distinct species.
- Professor Rütimeyer
His osteological studies on Indian humped and common cattle are cited as evidence for their specific distinctness.
Key passages
“From this fact we must conclude either that the aboriginal parent-species at first produced perfectly fertile hybrids, or that the hybrids subsequently reared under domestication became quite fertile.”
We must decide whether the original wild species initially produced fully fertile hybrids, or whether the hybrids later became fertile through domestication.
Darwin presents the key dilemma regarding hybrid fertility in domesticated animals.
“It is impossible to study the several memoirs and works of those two conscientious and admirable observers, Kolreuter and Gartner, who almost devoted their lives to this subject, without being deeply impressed with the high generality of some degree of sterility.”
Reading the detailed studies of Kölreuter and Gärtner, who dedicated their lives to this topic, one cannot help but notice how common some level of sterility is.
Darwin acknowledges the general prevalence of sterility while later questioning its universality.
“I think no better evidence of this can be required than that the two most experienced observers who have ever lived, namely Kolreuter and Gartner, arrived at diametrically opposite conclusions in regard to some of the very same forms.”
The fact that Kölreuter and Gärtner reached completely opposite conclusions about the same species shows how uncertain the evidence from sterility is.
Darwin uses the disagreement between experts to argue that sterility is not a reliable species criterion.