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.

13/484 (page IX)

FOREWORD By J. B. S. HALDANE Department of Biometry, University College, London Discussions on evolution must be very hard to arrange. At that held at Princeton in 1947 the participants were mainly geneticists and palaeonto¬ logists; at that for which I have been asked to write the foreword, palaeontology was not represented. Its place was taken by various forms of experimental biology. Just because palaeontologists must consider evolutio n, while experimental biologists need not do so, the results of the Oxford sym¬ posium are harder to summarize than those of the symposium at Princeton. I shall first take advantage of having the last word by defending myself, in my capacity of mathematical geneticist, against Waddington's criticism that 'very few qualitatively new ideas have emerged from it'. I think that some of them have emerged so completely that their origin is forgotten. Darwin apparently thought that variation could only be conserved by the effects of environmental differences in each generation. Fisher first showed clearly that in large populations it diminished with extreme slowness apart from the effects of natural selection, and Hagedoorn that it would diminish at a measurable rate in small populations. Wright then produced the qualitatively new idea of 'drift' or random evolution in small populations, which, in the present symposium, was attacked by Sheppard, Dowdeswell and Ford, and supported in a modified form by Spurway. Again, Penrose and Haldane first showed that some genes which seriously lower human fitness are only kept in being by mutation. Perhaps this idea has not emerged, for many people believe that human races could be permanently 'purified' from such genes by negative eugenics. Another idea which seems to me qualitatively new is that, because a selective advantage of the heterozygote over both homozygotes will preserve both of a pair of allelomorphs indefinitely, we may expect most of the genetic variation in an outbred population to be due to genes with this peculiar property. Such ideas as these pass rapidly from being mathematical theorems to being common sense. Other ideas with a superficial appeal to common sense, for example that dominants must oust récessives, appear to require mathematical disproof to prevent their spread. Mathematical biologists have also suggested what other biologists should measure. Here Lerner's notions of the selective differential, that is to say the difference between the average value of a character in the parents of the next genera-