The Origin of Species · Chapter
Distinct Species Present Analogous Variations, So That a Variety of One Species Often Assumes a Character Proper to an Allied Species, or Reverts to Some of the Characters of an Early Progenitor explained
Darwin argues that species of the same genus, sharing a common ancestor, often vary in analogous ways, with varieties mimicking other species or reverting to ancestral traits.
What happens
Darwin argues that species of the same genus, sharing a common ancestor, often vary in analogous ways, with varieties mimicking other species or reverting to ancestral traits. He uses examples from pigeons, horses, and asses to show that such variations and reversions are best explained by common descent and latent hereditary tendencies, rather than independent creation.
Themes in this chapter
Common Descent and the Tree of Life
Darwin uses analogous variations and reversions across species of the same genus to support descent from a common progenitor.
Variation and Inheritance
Discusses latent tendencies, reversion after many generations, and the inheritance of rudimentary organs.
Domestication and Artificial Selection
Uses domestic pigeon breeds and horse breeds as examples of analogous variation and reversion.
Characters to notice
- Charles Darwin
Author and narrator, presenting evidence for analogous variation and reversion.
- Mr. Blyth
Reported a specimen of hemionus with a distinct shoulder-stripe.
- M. Naudin
Observed analogous variations in the gourd family.
- Mr. B. D. Walsh
Discussed analogous variations in insects under natural conditions, grouping them under his law of equable variability.
- Pallas
Described the koulan with a double shoulder-stripe.
- Asa Gray
Figured a quagga specimen with zebra-like bars on the hocks.
Key passages
“As all the species of the same genus are supposed to be descended from a common progenitor, it might be expected that they would occasionally vary in an analogous manner; so that the varieties of two or more species would resemble each other, or that a variety of one species would resemble in certain characters another and distinct species, this other species being, according to our view, only a well-marked and permanent variety.”
Since species of the same genus share a common ancestor, they should sometimes vary in similar ways, causing varieties of different species to look alike or a variety of one species to resemble another species, which itself is just a distinct, stable variety.
Darwin explains that analogous variation is expected under common descent.
“When a character which has been lost in a breed, reappears after a great number of generations, the most probable hypothesis is, not that one individual suddenly takes after an ancestor removed by some hundred generations, but that in each successive generation the character in question has been lying latent, and at last, under unknown favourable conditions, is developed.”
When a lost trait reappears after many generations, it is more likely that the trait remained hidden in each generation and only emerged under favorable conditions, rather than a sudden leap back to a distant ancestor.
Darwin proposes latent heredity as the mechanism for reversion.
“To admit this view is, as it seems to me, to reject a real for an unreal, or at least for an unknown cause. It makes the works of God a mere mockery and deception; I would almost as soon believe with the old and ignorant cosmogonists, that fossil shells had never lived, but had been created in stone so as to mock the shells now living on the seashore.”
Accepting independent creation would mean preferring an imaginary or unknown explanation over a real one, making divine creation seem deceptive—like believing fossils were placed in rocks to mimic living shells.
Darwin criticizes the special creation view as implausible and deceptive.
