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.

20/484 (page XVI)

xvi FOREWORD Steven has studied the British mainland race of the vole Clethrionomys glareolus and three larger races confined to islands off Britain, which have sometimes been given specific rank. He has made six of the possible crosses, but the mainland and insular forms cross with difficulty, perhaps because of innate differences in behaviour. Some at least of the colour differences are due to a single gene, and a difference in tooth structure may be so. It seems likely that these differences have evolved within the last 9000 years. Unfortunately it is not yet known whether the hybrids between the mainland and insular forms are fertile. Such research is difficult and inevitably slow, but it is as direct an attack on the problem of the origin of animal species as can at present be made. Spurway crossed four races, morphologically separable and generally regarded as subspecies, of Triturus cristatus from England, Italy, Hungary and the Caucasus. The hybrids were vigorous and fertile, but the mortality among their progeny and the upset of spermatogenesis demonstrated by Callan suggest that the differences between the races are near to the level which would justify us in giving them specific rank. As in the Primula species, a number of easily visible taxonomic characters are determined by single genes, Spurway suggests that the function of skin colours is to favour escape from predators, and that the intersubspecific differences may be related to the geographical distribution of predators. The subspecies differ in respect of translocations, and Spurway contends that these could not have arisen as the result of the separation of a large population by geographical barriers. They must, she argues, have become established in populations derived from a small number, perhaps a single pair, of parents. Hundreds of similar studies have been made on plants, perhaps for the evolutionary reason which Spurway suggests, and a few on insects ; but this is, I think, the first such study on a vertebrate species, or Rassenkreis. We must now try to draw these various lines of research together. S. Manton's contribution is in a class by itself. The phylogeny of patterns of movement is as valid a contribution to evolution as is the phylogeny of structures or of organic compounds. Mantón has done for a phylum what comparative ethologists have done for small vertebrate groups such as the Anatidae. But her analysis seems to me to go deeper than theirs because she has consistently attempted to interpret movements in terms of their function, while ethologists rather deliberately avoid such an interpretation. She agrees with them in postulating considerable persistence of habit. Our successors will perhaps know whether this can be explained by per¬ sistence of neural anatomy. Her work may be compared with the com¬ parative study of mitosis, meiosis and gastrulation, but has the advantage that fossil chromosomes and gastrulae are not available, whereas not only