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.

17/484 (page XIII)

FOREWORD xiii jointly on development is particularly important to workers both on artificial selection and on species-crossing. The last section, on the evolu¬ tion of genes, is tantalizingly short. Pontecorvo suggested how this may have occurred, at least in some cases. Waddington's positive contribution to the discussion opened with a brief account of choices of environment by Drosophila mutants. If followed up, this work will not only be an important contribution to the genetics of behaviour, but will suggest that apparently unadaptive characters can be selected because the genes which determine them also affect behaviour. His distinction between 'normalizing' and 'stabilizing' selection is im¬ portant. He further described his recent work on selective breeding from flies which had or had not responded to a temperature shock by developing crossveinless wings. After fourteen generations the former line began to develop crossveinless wings without any temperature shock. Such a process had been postulated, but never clearly demonstrated, though Bateson's work on bolting in mangolds came near to doing so. It is obviously of great evolutionary importance, but its full genetical analysis demands much further work. Hovanitz, Sheppard, and Dowdeswell and Ford, all dealt with poly¬ morphism in Lepidoptera. Hovanitz showed that the colour polymorphism of females of Colias species is also a polymorphism for behaviour, or a polyethism, to coin a word; as is probably the case with Waddington's Drosophila mutants. He was able to explain the dines in the frequency of the two colour types on the basis of their behaviour. Sheppard continued Fisher and Ford's work on a colony of Panaxia dominula in which the frequency of a gene fell from about io% in 1939 and 1940 to about 3% from 1947 onwards. This gene affects colour pattern, larval survival, prédation by birds, and fertility. It also affects mating behaviour, females tending to mate with males unlike them. In spite of all this information it is not known why the gene in question was more frequent in the past than now, or whether it may be expected to persist, and if so why it is absent in most populations of the species. In fact, the paper demonstrates the immense difficulty of fully analysing even a very simple evolutionary change in an isolated population. Indeed, I have little doubt that if Sheppard knew less than he does about this insect, he could frame a more intellectually coherent theory! Dowdeswell and Ford described the polymorphism of wing spotting in Manióla jurtina in England and Ireland, including Man and the Scillys. They present population estimates, and biometrical data of great interest. The distribution of female patterns is uniform over most of England and Ireland, but changes greatly in the southwest, while different small Scilly