Neo-Darwinism / R.J. Berry.

  • Berry, R. J. (Robert James)
Date:
1982
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Neo-Darwinism / R.J. Berry. Source: Wellcome Collection.

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    38 EVOLUTIONARY GENETICS variation and strong selection pressures discussed in previous sections. The fitness of an individual or genotype must be regarded as a variable in exactly the same way as, say, birth rate or gene frequency. Now the fitness of an individual is the outcome of all its developmental and physiological processes; strictly speaking fitness is not a genetic trait but an epigenetic one, i.e. resulting from the interaction of gene-controlled processes (Fig. 4-1). In a few cases the contribution of different genes to fitness has been worked out. For example, two genes have been identified as contributing to resistance to a disease called foul-brood in honey bees: one determines 'larval cell uncapping' and the other 'larval removal'. Wild-type alleles at both loci.are Parental types Drones Nonhygienic: Fig. 4-1 Fitness is an interaction between many genes and the environment. Resistance to foul brood disease in bees is determined by two genes; only the doubly recessive workers (ы/м, r/r) will both uncap cells containing dead larvae, and also remove the larvae. (From BERRY, 1977.) necessary for hygienic behaviour, which protects the colony from the disease. The effect of gene action on behaviour affecting fitness is also well shown by genes involved in tyrosine metabolism: black rabbits are less timid than agouti ones, permitting longer feeding and hence survival in food-limited populations despite visual selection against them; melanic cats are more successful at breeding under dense urban conditions than lighter animals; dark phase Arctic skuas (or jaegers) pair more readily and therefore earlier than ones of pale or intermediate phase; melanic rock doves breed all the year round, and hence increase in frequency when food is permanently available, as in towns; human phenylketonurics (who are mentally defective unless treated) are less pigmented than their normal sibs (Table 5). And so on: it would be easy to extend greatly the list of inherited fitness variation. From the evolutionary point of view the point to recognize is that fitness variation is extremely common. Ecologists have developed an interest in recent years in what has come to be called 'evolutionary ecology', involving the breeding success of organisms in different niches and how they adjust to change. However, evolutionary ecology is unlikely to advance far unless it is linked to a study of what may be called 'evolutionary genetics'. Criticisms about the effectiveness of selection are inevitable if the action of selection in natural conditions is not properly understood. The popular understanding of selection