Endurance of life : the implications of genetics for human life / Macfarlane Burnet.

  • Burnet, F. M. (Frank Macfarlane), Sir, 1899-1985.
Date:
1978
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Endurance of life : the implications of genetics for human life / Macfarlane Burnet. Source: Wellcome Collection.

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    30 Endurance of Life survival and to a wide variety of chance vicissitudes—included in the concept of genetic drift—which can sometimes even allow a mildly disadvantageous gene to prosper. Experience and logic applied to human populations and to wild populations of fruit fly, Drosophila, indicate that in both species almost every individual carries a proportion of recessive genes which if they were phenotypically expressed in double (homozygous) form would give rise to some demonstrable and disadvantageous change of structure or function. In man, the number has been estimated to average somewhere between five and ten per individual. In addition to these skeletons in the genetic cupboard we can be certain that there are much larger numbers of neutral or nearly neutral mutations also awaiting opportunity for recombination. It is from such new combination that most of the advantages that we recognize as contributing to evolutionary progress arise. To many people this accumulation of tiny improvements by ran¬ domly accumulated mutations seems completely inadequate to account for the eagle's eye, the peacock's tail, or the human brain. The only answer is to stress that the whole process of sexual repro¬ duction ensures a maximal likelihood of testing out every possible mixture of the latent potentiaUties of past mutations yet at the same time retaining most of them in the gene pool for further testing. Perhaps one should add that the sequence of mutation and recom¬ bination, selection and survival, as the basis of evolution had been clearly formulated as a result of the work of Darwin, Weismann, Mendel, Haldane, Morgan, Sewall Wright and Fisher by 1940. Over thirty-seven more years it has been found adequate and there is probably no biologist of standing who would not support the dictum that there is just no other conceivable interpretation of the history and nature of hfe. In summary then, life long ago discovered in DNA an immensely versatile mechanism for, one might say, converting error into infor¬ mation. The possibility of erroneous insertion of nucleotide units in the linear strands of DNA must have been present since the first DNA took form. As the enzymes controlling DNA became better organized, error-proneness diminished but never became zero and could be changed when required, e.g. in relation to the repair of different types of DNA damage by mutagens. Errors accumulated more or less constantly during evolution and were either lost by selective processes or in due course were incoфoгated into standard pattern. At any one time the genetic pool of a species contains large numbers of mutant alternative configurations constantly being tes-