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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    The other side of this picture is that the relations of deter¬ minism and uncertainty involved in the succession of processes covered by the superficial and popular terms heredity, variation and evolution, have hitherto been utterly concealed from biologists, physicists and philosophers alike. Now that they are clear in principle there are therefore likely to be widespread doubts as to their meaning and their fundamental position in the understanding of life. It is therefore worth while to sum up the evidence. Genetic and physiological studies have changed our views of determinism in life in the following ways:— In the first place, the limited resemblances of parents and offspring are not due to the deterministic principle of heredity directly and alone. They are due to the interference of the uncertainty not only of the environment but also of mutation and recombination, an uncertainty which can be abolished in parthenogenesis and in one-egg twinning. It is the Mendelian paradox that brothers differ by heredity, and on account of heredity, which alters the whole explanatory scheme. In the second place, the uncertainty of mutation and recom¬ bination is in practice irrelevant to the individual. We find it because without it evolutionary change could never have occurred and incipient life would have been snuffed out. It means that parents and offspring have an unpredictability in their genetic relationship. But, on the Schrödinger principle, populations remain genetically predictable. Finally, the force of heredity is vastly greater than the founders of genetics thought. On the one hand, heredity itself exists in part in forms beyond Mendelian analysis, in polygenes and in the cytoplasm. On the other hand, the environment has a fluctuating role. Only its highest value achieved in a plant (and in an individual, not a population) enables us to describe the result of development as due to a simple reaction of geno¬ type and environment. In all animals the genotype itself chooses the environment. And in man, the genotype can create the environment. 392