Selected genetic papers of J.B.S. Haldane / edited with an introduction by Krishna R. Dronamraju.

  • Haldane, J. B. S. (John Burdon Sanderson), 1892-1964.
Date:
1990
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Selected genetic papers of J.B.S. Haldane / edited with an introduction by Krishna R. Dronamraju. Source: Wellcome Collection.

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    fruitfully on the level of beanbag genetics, except to say that several differ¬ ent genotypes may achieve good homeostasis, while other combinations of the genes concerned are less well adapted for homeostasis, though they may have other advantages. Even this is a mere speculation. ТЪеге may be only one adaptive peak in Wright's sense. As I happen to be responsible for some of the mathematical groundwork of enzyme chemistry [32], I can say that the mathematical basis of physio¬ logical genetics is about fifty years behind that of beanbag genetics. If a metabolic process depends on four enzymes acting on the same substrate in succession, one can calculate what will happen if the amount of one of them is halved, provided that one is working with enzymes in solution in a bottle. We know far too little of the structural organization of living cells at the molecular level to predict what will happen if the amount is halved in a cell, as it is in some heterozygotes. If the enzyme molecules are arranged in organelles containing just one of each kind, the rate of the metabolic process will probably be halved. But if they are in a random or a more complicated arrangement, it may be diminished to a slight extent, or even increased; for the activities of some enzymes are inhibited by an excess of their substrate. This is a conceivable cause of heterosis, though I do not think it is likely to be common. Now let me pass over to a counterattack. One of the central theses of Mayr's book is that speciation is rarely if ever sympatric. One species can only split into two as the result of isolation by a geographic barrier, save perhaps in very rare cases. Let me say at once that Mayr's arguments have convinced me that sympatric speciation is much rarer than some authors have believed, and a few still believe. But when, in his chapter 15, he dis¬ cusses other authors' hypotheses as to how sympatric speciation might oc¬ cur, his arguments are always verbal rather than algebraic. And sometimes I find his verbal arguments very hard to follow. Thus, on page 473 he makes seven assumptions, of which (i) is Let A live only on plant species I, and (4) is Let A be ill adapted to plant species 2. These two assump¬ tions seem to me to be almost contradictory. If A lives only on species i, the fact that it is ill adapted to species 2 is irrelevant. If emus only live in Australia, the fact that they are ill adapted to the Antarctic has no influence on their evolution. If the assumptions had been (i) Let A females only lay eggs on species i, and (4) Let A larvae (not all produced by A mothers) be ill adapted to species 2, I could have applied mathematical 355 13