The facts of life / C.D. Darlington.

  • C. D. Darlington
Date:
1953
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The facts of life / C.D. Darlington. Source: Wellcome Collection.

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    relation to his survival of the fittest. Obviously he could not go very far. And beyond a certain point he was bound to be led astray. His units of heredity were derived from the observation of constancy in tissues and hence from differentiation. They were therefore subject to the effects of the environment. It was in this way that he was led to assume the inheritance of the effects of use and disuse. This in turn inspired Darwin to give Spencer's factually static Units a fictitious circulation and to call them Pangenes. So that both together fell into the Lamarckian pit. Let us see how Darwin presented the ancient theory of pangenesis in 1868:— I assume that cells, before their conversion into completely passive or formed material throw off minute granules or atoms, w^hich circulate freely throughout the system, and w^hen supplied with proper nutriment multiply by self-division, subsequently becoming developed into cells like those from which they were derived. These granules for the sake of dis¬ tinctness may be called cell-gemmules, or, as the cellular theory is not fully established, simply gemmules . . . the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements. Hence speaking strictly it is not the reproductive elements, nor the buds, which generate new organisms but the cells themselves throughout the body (Animals and Plants Under Domestication, 2: 374). Here we see the theory of pangenesis, as imderstood by Aristotle, being expressed in the terms understood by the nineteenth century. But how strange are the assumptions that Darwin has to rely on! In sexual reproduction he assumes that many sperm or many pollen grains are necessary to fertilize one egg. He assumes that irregular distribution or contribution of pangenes will account for reversion and prepotency. He also assumes that sexual reproduction, does not essentially differ, as we have seen, from budding or self-division. And finally he assumes that the pollen may influence the colour of the hybrid fruit and that the sperm of one mating may influence the progeny of a later mating of the same mother. All these assumptions we must, one by one, examine and test. 64