The Variation of Animals and Plants Under Domestication

The book's central argument is that the extraordinary variation achievable through domestication demonstrates the power of selection as an evolutionary mechanism. Darwin intended Variation as the first installment of his 'big book'—a planned multi-volume expansion of the Origin that would present the full evidence for natural selection . The work assembles decades of evidence from breeders, fanciers, and horticulturalists showing that domesticated animals and plants exhibit far greater variation than wild species, and that unconscious selection—preservation of favored individuals without deliberate intent—can produce dramatic divergence over generations . Darwin argued that if human breeders could achieve so much in a few centuries, natural selection acting over geological time could achieve far more. The book thus serves as an empirical buttress to the Origin, answering critics who dismissed evolution as mere speculation .

Pangenesis was Darwin's 'provisional hypothesis' of heredity, presented in the second volume of Variation. The theory proposed that every cell in the body continually throws off minute particles called gemmules, which circulate through the organism, aggregate in the reproductive organs, and transmit heritable information to offspring . Darwin developed Pangenesis to fill a critical gap in his evolutionary theory: the Origin had demonstrated that natural selection acts on variation, but had not explained how variation arises or how traits are inherited. Pangenesis was intended to account for a wide range of phenomena including inheritance of acquired characters, reversion, regeneration, and graft hybridization . Darwin called it his 'beloved child' and firmly believed it would 'turn out true some day'—a conviction not shared by most of his contemporaries .

Reception was sharply divided but predominantly skeptical. Joseph Dalton Hooker, a close ally of Darwin on natural selection, called Pangenesis 'a stumbling block to me' and opposed the power Darwin vested in it to explain reproduction and inheritance . Thomas Huxley, who had urged Darwin to publish, reportedly accused him of rehashing eighteenth-century natural history; Darwin conceded that his views resembled Buffon's but insisted on a fundamental distinction: Buffon did not suppose that each cell throws off a bud, whereas Pangenesis was grounded in cell theory . The Athenaeum dismissed Variation as containing 'nothing more in support of origin by selection' than repeated 'guesses' . The Daily Review called Pangenesis 'so extraordinary and unheard of' as to show to what straits Darwin was reduced . Even sympathetic reviewers like the London Review, which called Pangenesis 'the keystone to the philosophic arch,' did not defend its empirical basis .

Francis Galton, Darwin's half-cousin and a prominent scientist, attempted to test Pangenesis experimentally by transfusing blood between rabbits of different colors to see if gemmules would transmit heritable traits. His experiments produced negative results, which he published in 1871, arguing that they failed to support Pangenesis . Darwin responded publicly in Nature, rebuking Galton for claiming to have tested a hypothesis he had misunderstood—Darwin's gemmules were not necessarily carried in blood. Galton answered 'in kind,' and the exchange became a very public dispute . While the experiments did not definitively refute Pangenesis (since the blood-transfusion method tested only one possible transport route), the controversy damaged the theory's credibility. The dispute illustrated the difficulty of empirically testing a hypothesis as protean as Pangenesis, whose gemmules were defined partly by their capacity to evade easy detection.

The second edition, published seven years after the first, embodied Darwin's continued research and correspondence. A contemporary review noted that the emendations were 'very slight' on most points, with no retractions or modifications that disturbed his general conclusions . However, the chapters on Pangenesis and Inheritance were 'partially remodelled' and 'in some portions entirely recast' . Darwin also added a table of principal additions and corrections, demonstrating his transparency about revisions. This pattern—minimal concession on core claims, substantial revision of the speculative heredity theory—suggests Darwin understood that Pangenesis was his most vulnerable position and that its presentation, rather than its substance, required adjustment. The Saturday Review noted that any doubts about the soundness of the evidence 'must now be removed by the seven years' sifting to which it has been subjected' .

Pangenesis was made effectively obsolete after the 1900 rediscovery of Gregor Mendel's theory of particulate inheritance . Mendel's factors (later genes) explained heredity through discrete, independently segregating units, whereas Darwin's gemmules were conceived as circulating particles that blended and modified according to use and disuse. The Mendelian framework was mathematically robust and experimentally corroborated in ways Pangenesis never was . The irony is that Darwin's theory was, in a sense, more 'modern' than it appeared: gemmules were particles, and the theory acknowledged that inheritance had a material basis. But Darwin's commitment to blending inheritance—and his Lamarckian allowance for acquired characters—placed Pangenesis on the wrong side of the particulate theory that would define twentieth-century genetics. The historian Conway Zirkle noted that Pangenesis was 'as old as the belief in the inheritance of acquired characters,' endorsed by Hippocrates and others, though Darwin's version used cell theory to give it novel specificity .