Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

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

Credit: Evolution. Source: Wellcome Collection.

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FOREWORD Xvii the limbs but also the tracks of extinct animals are preserved. When a dozen studies of similar amplitude have been completed, we shall have a well- defined branch of evolutionary studies with its own generalizations and its own vocabulary. Meanwhile we can only salute the pioneers. Other studies point in the same direction. Some day we shall be able to compare the ways in which different mammals cope with the problem of antigenic diversity, different bacteria with that of adaptation to new diets, different plants with that of coexistence with species which can hybridize with them, and so on, Needham's study of the adaptive character of vertebrate nitrogenous excretion is a model for such work. It is notable, however, that such comparative studies, though they tell us more and more about what has happened in the course of evolution, tell us very little about how and why it happened. This problem, so far as we can see at present, can only be solved by combined genetical and ecological research, and it is notable that six out of the ten contributions which were mainly genetical included ecological data. We do not know whether the most important contributions to evolution theory will come from the study of polymorphic or polytypic species. Hovanitz's finding that С olios gigantea females are all white in Alaska and all yellow in southern Canada shows that polymorphism is a possible step towards speciation. That polymorphism is at least a possible step in a major evolutionary change is shown by the case of Acentropiis niveus. In this moth there are two types of female, one with normal wings and an aerial life, the other with reduced wings and spending a considerable time under water. If sympatric speciation ever occurs, it presumably occurs as a result of polyethism, either genetically determined, as in Hovanitz's case, or environmentally determined, for example by larval conditioning, as in Thorpe's case. Waddington's paper suggests a method not involving 'inherited memory' by which the second condition could pass over into the first, Allopatric speciation undoubtedly occurs, and the last four papers dealt with what can at least plausibly be interpreted as stages in this process. But we know extremely little about the adaptive values of the individual taxonomic characters, less than we do in the case of polymorphic species. Here the next step may be to study the ecological adaptability of segregates from the hybridization, such as the well-known horticultural variety Primula ^juliana* which contains genes derived from both P. vulgaris and P. juliae, under natural conditions. A number of the genetical contributors are finding that they must study not only ecology but ethology. The structure of an animal population is ethologically determined ; so is that of a population of entomophilous