Darwin only published one account of his provisional hypothesis of pangenesis, and that is to be found in chapter xxvii of his bookThe Variation of Animals and Plants under Domestication, the first edition of which is dated 1868. The absence of any earlier account in Darwin's works has led some to assume that he had recourse to this hypothesis only a short time before the published date of the book containing it, and on the basis of this assumption they have (...) asserted that he produced it as a part of his defence of the theory of evolution against the criticisms made of it by the physicists Sir William Thomson, afterwards Lord Kelvin, and Fleeming Jenkin. But to make such an assertion is to ignore the fact that Darwin had already sent his manuscript of pangenesis to Huxley in the year 1865, two years before Fleeming Jenkin's article appeared and three years before Lord Kelvin openly attacked the evolutionary theory. The discovery of this manuscript of pangenesis has, therefore, some importance, for it should reveal Darwin's conception of pangenesis in 1865. (shrink)

‘Non-Progression’, the interpretation of life-history launched by Lyell in 1830 and defended by him for over twenty years, can be summarized as follows. Palaeontologists, Lyell contended, should assume that at every period of the earth's recoverable past, each class of plants and animals has been represented somewhere on earth. Species have been created solely as responses to perpetually shifting environmental conditions, and not as temporally conditioned stages in the unique unrolling of a grand plan. If certain environments are especially suited (...) to reptiles, then the Creator tailors collections of beautifully adapted terrestrial, aquatic, and even aerial reptiles for them—as He did, for example, for the environments recorded in the British Jurassic; as He did, much more recently, for the Galapagos Islands; and as He will do again, if conditions somewhere on earth ever force mammals into extinction, leaving ecological niches which can more suitably be filled by reptiles. If, for example, changes in the topography and climate of the Sussex Weald eventually lead to the re-establishment of an environment that particularly suits iguanodons, then iguanodons will assuredly appear there again. The essential point about Lyell's interpretation is that time does nothing to determine a particular flora and fauna. When designing a new animal, the Creator, according to Lyell's view, has to take into account only the creature's or plant's destined environment: He has to consult no timetable, or lineage, governing the production of new forms. In notes for a speech given in 1852 Lyell reduced his interpretation to the epitome, ‘Adaptation to geographical circumst5 not progressive develop the real history of past changes’. (shrink)