The Origin of Species · Chapter
Hybrids and Mongrels Compared, Independently of Their Fertility explained
This chapter compares the offspring of crossed species (hybrids) and crossed varieties (mongrels) in respects other than fertility.
What happens
This chapter compares the offspring of crossed species (hybrids) and crossed varieties (mongrels) in respects other than fertility. Darwin, drawing heavily on Gärtner's experiments, argues that the differences between hybrids and mongrels are minor and gradational, while their similarities in variability, reversion, prepotency, and resemblance to parents follow the same laws. This supports the view that species and varieties are not fundamentally distinct.
Themes in this chapter
Variation and Inheritance
The chapter examines variability in first-generation and subsequent generations of hybrids and mongrels, and the laws of resemblance to parents, supporting the idea that variation and inheritance follow common principles across species and varieties.
Domestication and Artificial Selection
Mongrels are mostly derived from domestic varieties, which have undergone recent variability due to domestication, and this is contrasted with hybrids from wild species.
Characters to notice
- Gärtner
Gärtner's experiments are central to the comparison of hybrids and mongrels; he found few and unimportant differences between them.
- Kölreuter
Kölreuter's experiments are cited as opposing Gärtner's conclusion about hybrid differences when crossed with a third species.
- M. Naudin
Naudin insisted on the universal tendency to reversion in hybrids, based on experiments with cultivated plants.
- Max Wichura
Max Wichura doubted whether hybrids ever revert to parent forms, based on experiments with uncultivated willows.
- Dr. Prosper Lucas
Darwin agrees with Dr. Prosper Lucas that the laws of resemblance of offspring to parents are the same whether parents are of the same variety, different varieties, or distinct species.
Key passages
“Gartner, whose strong wish it was to draw a distinct line between species and varieties, could find very few, and, as it seems to me, quite unimportant differences between the so-called hybrid offspring of species, and the so-called mongrel offspring of varieties.”
Gärtner, who wanted to clearly separate species from varieties, found only minor and trivial differences between hybrids (from crossing species) and mongrels (from crossing varieties).
Darwin uses Gärtner's own data to undermine the species-variety distinction.
“The slight variability of hybrids in the first generation, in contrast with that in the succeeding generations, is a curious fact and deserves attention. For it bears on the view which I have taken of one of the causes of ordinary variability; namely, that the reproductive system, from being eminently sensitive to changed conditions of life, fails under these circumstances to perform its proper function of producing offspring closely similar in all respects to the parent-form.”
Hybrids in the first generation show little variability, but their descendants are highly variable. This supports Darwin's idea that variability arises because the reproductive system is sensitive to changed conditions and fails to produce offspring exactly like the parents.
Darwin links variability to reproductive system sensitivity, a key part of his theory.
“On the whole, I entirely agree with Dr. Prosper Lucas, who, after arranging an enormous body of facts with respect to animals, comes to the conclusion that the laws of resemblance of the child to its parents are the same, whether the two parents differ little or much from each other, namely, in the union of individuals of the same variety, or of different varieties, or of distinct species.”
Darwin agrees with Dr. Prosper Lucas that the rules governing how offspring resemble their parents are identical, regardless of whether the parents are from the same variety, different varieties, or different species.
This conclusion reinforces Darwin's argument that species and varieties are not fundamentally different.
