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A Brief History of Evolutionary Genetics

Part 5:  J.B.S. Haldane

©Paul Handford, 1998
photograph of JBS Haldane by Dr. K. Patau from  "Haldane and Modern Biology" (ed. K.R. Dronamraju), Johns Hopkins University Press, 1968.

Haldane was distinct from Fisher and Wright in terms of his disciplinary background and interests:  he was fascinated by chemistry and biochemistry.  Throughout his career in developing mathematical population genetics in concert with Wright and Fisher, he was always at pains to consider what was, or might be, going on at the chemical level.  Thus he writes:

Later he wrote  (note 1) some near-prophetic words on this theme: In several  respects, Haldane developed ideas intermediate between those of Fisher & Wright

Haldane's early career in genetics included some of the first studies in linkage in mammals, and an analysis of the mathematical consequences of selection in Mendelian populations  under a great variety of conditions and complexities.  In the process, he developed model systems very like those of Fisher.  He was initially persuaded, like Fisher, that deterministic selection, primarily of the effects of single genes, was the most powerful force in evolutionary change, and he saw populations as being effectively very large & panmictic.  However he differed from Fisher in supposing that some genes could have marked effects and give rise to large selective differentials (remember, Fisher saw tiny effects of allele substitution as the rule, conveniently giving him the possibility of very finely-tuned adaptations.)  Later, though, Haldane became convinced that interactions among genes could be important, and developed ideas which were very similar to those being produced, independently, by Wright.  Nevertheless, contrary to Wright, he believed that most populations, most of the time, are not highly subdivided and, therefore, not much subject to genetic drift, in the long run.

Haldane developed some ideas in evolutionary thinking which were, again, highly original and forward-looking - like his ideas on the chemistry of the gene & gene-replication quoted above.  As an example, we may note his adumbration of what was later to become (in 1964, with the papers of W.H. Hamilton) the theory of inclusive fitness and kin selection.  Quoting again from his 1932 book:

Haldane was concerned with diversifying, as well as adaptive, evolutionary change

At the time, (the 1920s and '30s), population genetics theory was concerned exclusively with processes internal to a population (it largely still is), and it was developing essentially separately from thinking about the larger-scale evolutionary phenomena, especially speciation - the evolution of new lineages.  Scientists studying speciation rarely had any acquaintance with, still less expertise in, population genetics:  their affinities were primarily with natural historians or systematists.  This disregard for matters concerned with diversification certainly characterised Fisher, and was largely true of Wright - indeed it was pretty much true of Darwin, too.  Haldane, on the other hand, did pay some attention to at least the earlier stages of lineage diversification.  Through his considerations of the conditions necessary for substantial evolutionary change, he came to believe that some form of isolation of a relatively small group of individuals may be necessary.  In discussing such isolated groups he says:

Thinking about diversification of species necessitates a close consideration of the ways in which character diversity is manifested in natural populations - its magnitude, its spatial patterning, its genetic basis, if any, and its adaptiveness or otherwise.  The investigation of the details of what can go on locally under different conditions of selection and drift is, in principle at least, a straightforward theoretical issue. This was the primary concern of Fisher, Wright & Haldane, as we have seen, and they did a thorough job.  But to make much headway in comprehending these larger-scale matters, it was indispensable to gain a clearer empirical picture of genetic populations in nature.  This, of course is the matter which had always involved the natural historians back to the time of Darwin and Wallace.  From this point on in our history, the attempt to describe the true nature of natural genetic populations was to assume much more importance.  The "Three Giants" had laid down a solid bed of theory describing what might be expected to happen within local populations;  our story continues with attempts to take this theory out of doors.


Note 1  Haldane, J.B.S.  1941  New Paths in Genetics.  Return to text.

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