Book: The Variation of Animals and Plants under Domestication

Overview
Charles Darwin’s 1868 two-volume study surveys how domesticated animals and plants vary, how breeders shape that variation, and what these patterns reveal about the mechanisms of evolution. Treating farms, gardens, fancier clubs, and herbaria as vast experimental grounds, he argues that the cumulative effects of selection, crossing, and altered conditions can produce forms as distinct as recognized species. The book extends and fortifies the argument for descent with modification by showing, in detail, how great change arises from small, heritable differences under sustained selection.

Method and Scope
Drawing on correspondence with breeders and horticulturists, historical records, and his own experiments, Darwin compares numerous breeds and varieties, with special attention to pigeons, fowls, rabbits, dogs, cats, and key crops and fruit trees. He distinguishes between methodical selection, in which desired traits are intentionally targeted, and unconscious selection, by which owners keep and propagate the individuals that best suit their purposes without explicit long-term plans. Both accumulate differences over generations, generating the extraordinary diversity of domestic races.

Variation under Domestication
Darwin emphasizes that organisms under new conditions of life exhibit greater variability. Changes in climate, food, and habits, along with relaxed struggle for existence, foster a wealth of minute differences. He catalogs “correlated” changes, whereby modifying one trait unintentionally alters others, and highlights the frequent “reversion” toward ancestral states when selection is relaxed or when varieties intercross. He also examines use and disuse, suggesting that organs strengthened by use or neglected by disuse may alter across generations, contributing to the suite of changes often seen in domestic forms, such as drooping ears or altered skulls.

Case Studies and Origins
Pigeons provide the best-resolved case: despite their dramatic differences, carriers, pouters, fantails, tumblers, Darwin argues that all descend from the rock dove, Columba livia, as shown by interbreeding, shared developmental traits, and occasional reversion. He traces fowls chiefly to the red junglefowl and domestic rabbits to the wild European rabbit, noting changes in bone proportions, brain size, and behavior under domestication. Dogs likely derive from multiple wild canids. In plants, he surveys cabbages, cereals, vines, apples, and more, documenting “sports” arising from bud-variation, such as the moss rose, and the capacity to fix new varieties through vegetative propagation. Across these examples, he stresses that large, breed-defining differences are the cumulative product of selection acting on abundant small variations.

Inheritance and Pangenesis
To unify phenomena such as ordinary inheritance, atavism, graft-hybridization, regeneration, and the transmission of acquired injuries, Darwin proposes the provisional hypothesis of pangenesis. He suggests that all cells emit minute “gemmules” that circulate and aggregate in reproductive tissues, thereby conveying information from the whole organism to its offspring. Though speculative, pangenesis is presented as a causal framework for the observed facts that like produces like, that specific ancestral traits can reappear after many generations, and that buds and grafts can transmit varietal characters in plants. He also treats prepotency (unequal transmission by some parents), inheritance at corresponding ages, and sex-limited traits.

Species, Fertility, and Selection
Darwin confronts the species–variety boundary by showing that domestic races can differ more than allied wild species yet remain connected by gradations and are generally fertile when crossed. He contends that sterility is not a defining, divinely imposed barrier but an incidental outcome that varies with conditions. The efficacy of artificial selection, especially unconscious selection practiced over centuries, provides an analogy for natural selection: if human preferences can reshape organisms profoundly, then prolonged selection by nature, acting on survival and reproduction, can generate the wider diversity of life.

Significance
The book is both compendium and argument. By assembling thousands of observations on heredity, variation, and breeding practice, Darwin demonstrates that evolutionary change is neither sudden nor miraculous but the expected outcome of heritable variation filtered by selection. Domestication, he shows, illuminates the laws of variation and inheritance that also govern change in nature, strengthening the case for common descent and the creative power of selection.