of a few alien immigrants is correspondingly plication of species, so that the process of greater. Both authors stress the influence of splitting is a fundamental one. Oasses and popUlation size, but for one the important orders of organisms may persist for long feature is the occasional extreme reduction of periods with approximately constant numbers numbers (the founder effect), while for the of taxa, however, so that it is not necessarily other it is the dispersive effect on gene fre• always the most important one. Mayr is clearly quency brought about by moderate popula• concerned with species multiplication (he calls tion size. Isolation 3lso plays a pivotal part. it true speciation) whereas Wright's theory For Mayr it is an essential prerequisite for applies to phyletic speciation. evolutionary change; for Wright the isolation Peripheral, central distribution patterns must be no more than partial between locally exist in many groups and there is no generally adapted colonies. accepted explanation for them. In order to One factor to be considered is the relation decide between the theories discussed it is between species formation and . necessary to know more about the various Species may be chronological successors in a factors involved. In particular, we require a single phylogenetic line. Geographical isolation, better understanding of the meaning of on the other hand, can result in the formation coadaptation and of the probable effect of a of two species from one, and these may then given amount of migration on the chance that coexist. Evolution has certainly led to a multi- a coadapted gene complex will develop.

Suggestions for further reading

Suggestions for further reading Creed, E.R (1971), Ecological Genetics and The current research is to be found in journals Evolution. Essays in Honour of E.B. Ford, such as The American Naturalist, Evolution, Blackwell, Oxford. Genetics, Heredity, Theoretical Population Crow, J.F. and Kimura, M. (1970), An Intro• Biology etc; and in a host of other journals duction to Population Genetic Theory, with a more specialised interest in one aspect Harper and Row, New York. or another. Oassified abstracts which help to A comprehensive and up to date account. draw the work together are provided by Falconer, D.S. (1960), Introduction to journals such as Genetics Abstracts. Regular Quantitative Genetics, Oliver and Boyd, review articles appear in Advances in Genetics Edinburgh. and Annual Review of Genetics. The follow• A very clear account of the material in ing is a list of major sources in which the work referred to in this book will be found. Ch. 2 is contained in the first part of this book. Cavalli-Sforza, L.L. and Bodmer, W.F. (1971), Ford, E.B. (1975), Ecological Genetics, 4th The Genetics of Human Populations, Edition, Chapman and Hall, London. Freeman, San Francisco. Hecht, M.K. and Steere, W.C. (1970), Essays

61 in Evolution and Genetics in Honour of Process, Allen and Unwin, London. Theodosius Dobzhansky, North-Holland, Mayr, E. (1963), Animal Species and Evolution, Amsterdam. Harvard University Press, Cambridge, Mass. Kettlewell, H.B.D. (1973), The Evolution of Mettler, L.E. and Gregg, T.G. (1969), Popula• Melanism, Qarendon, Oxford. tion Genetics and Evolution, Prentice-Hall, Kimura, M. and Ohta, T. (1971), Theoretical Englewood Cliffs, N.J. Aspects of Population Genetics, Princeton Murray, J. (1972), Genetic Diversity and University Press, Princeton, N.J. , Oliver and Boyd, Puts the case for selectively neutral genes Edinburgh. in evolution. Provine, W.B. (1971), The Origins of Theoretcal Kojima, K. (1970), Mathematical Topics in Population Genetics, Chicago University Population Genetics, Springer-Verlag, Press, Chicago. Berlin. Sheppard, P.M. (1973), Practical Genetics, This volume is an important recent review Blackwell, Oxford. of a range of topics by authorities in their Contains a section by Sheppard on popula• respective fields. There are articles of direct tion genetics which includes a simple com• relevance to this book by Crow, Sved and puter simulation program. Mayo, Turner and Wright. Not as mathe• Sheppard, P.M. (1975), Natural Selection and matical as its title suggests. Heredity, 4th Edition, Hutchinson, London. Lerner, I.M. (1958), The Genetic Basis of Spiess, E.B. (1962), Papers on Animal Popula• Selection, Wiley, New York. tion Genetics, little, Brown and Co; Boston. Lewontin, R.C. (1973), Population Genetics, Strickberger, M.W. (1968), Genetics, Macmillan, Ann. Rev. Genetics, 7, 1-17. New York. Lewontin, R.C. (1974), The Genetic Basis of A standard genetical text. Evolutionary Change, Columbia University Wallace, B. (1970), Genetic Load, its Biological Press, New York. and Conceptual Aspects, Prentice-Hall, A major treatment of current issues. Essential Englewood Cliffs, N.J. reading to gain a picture of the present state Wright, S. (1969), Evolution and the Genetics of population genetics. of Populations. Vol. 2. The Theory of Gene Mather, K. (1973), Genetical Structure of Frequencies, Chicago University, Chicago. Populations, Chapman and Hall, London. An important source but not easy to read. Mather, K. and Jinks, J.L. (1971), Biometrical Gives references to earlier papers. Genetics. The Study of Continuous Varia• Chapter 4. Genetics of Cepaea. The material tion, Chapman and Hall, London. of this chapter is discussed by Ford (1975), Mayr, E. (1954), Change in Genetic Environ• Murray (1972) and Sheppard (1975). ment and Evolution, in Huxley, J., Hardy, The reader is referred to these sources for A.C. and Ford, E.B. (1954), Evolution as a the original papers.

62 Index

Allison, A.C. 29 inversions, 47 Apostatic selection, 42 Arnold, R.W. 42 Effective population size (Ne ), 23 Epistatic interaction, 8 Birch, L.c. 33 and chromosome number, 51 Bishop, I.A. 27 and selection, 48 Bodmer, W.F. 30 see coadaptation Equilibrium, 13, 16 Cain, A.I. 38, 40, 42 Hardy-Weinberg, 13 Cavalli-Sforza, L.L. 30 stable, unstable, 14, 18 Cepaea hortensis, 39 Cepaea nemoralis, 36 Fisher, R.A. 7,10,33,47 apostatic selection, 42 Fitness, 17 climatic selection, 41 absolute, relative, 17, 60 co adaptation, 40 see selective value genetics, 36 Ford,E.B.24,33,49 sampling drift, 36 Founder effect, 23, 58 selective , 38 stationary gene frequency Galton, F. 9 distribution, 37 Gene, major, 8 Clarke, B.C. 39, 40, 42 controlling continuous variation, 9 Clarke, C.A. 26,47,49 expression, 8 Coadaptation, 40, 58 pleiotropic, 9 see epistatic interaction Gene frequency, 8, 13 Cost of selection, 53 Genetic load, 51 see load see load Crosby, I.L. 48 Genetic , 24 Currey, I.D. 40 Genetic variance, 11 source of, 47 Dispersive effects, 21 G6PD-deficiency, 30 Diver, C. 36 Goodhart, C.B., 40 Dobzhansky, T. 31,47 Dominance, 8 Haldane, I.B.S., 7, 25,52 evolution of, 47 Hardy-Weinberg equilibrium, 13 Drift, 21 Harris, H., 44 Drosophila pseudoobscura, 31 Heterozygote advantage, 18,29,42 coadaptation, 58 evolution of, 46

63 Inbreeding, 10, 23 Selective value (w), 17 Industrial melanism, 24 Sheppard, P.M., 26, 33, 38,47,49 Intensity of selection, 52 Shifting balance theory of evolution, 59 Sickle cell polymorphism, 29 Kettlewell, H.B.D., 25 Stationary gene frequency Kimura, M., 22, 54 distribution, 37 Super-genes, origin of, 49,50 Lamotte, M., 37 Systematic effects on gene frequency, 15 Lewontin, R.C., 44, 54 migration, 15 Load, mutational, 51 mutation, 16 segregational, 52 selection, 16 substitutional, 53 Thoday, 1.M., 12 Mayr, E., 57,61 Turner, 1.R.G., 49 Mean fitness (w), 17 change in, 20, 59 Variance, components of, 11 Migration, 15 additive, 12 inhibiting effect of, 57 environmental, 12 Muller, H.l., 51 non-additive, 12 Murray, 1.1., 40 source of, 47 Mutation, 16, 51 Variation, biometrical or continuous, 9 Non-recurrent change in gene frequency, 23 Weldon, W.F.R. 9 Panmictic (panmixia), 8 Williamson, M.H., 34 Peppered moth, 26 Wright, S., 7,13,14,23,31,37,40,59 Peripheral diversity in species, 57 Pleiotropism, 9, 35 Polymorphism, genetic, 24 methods of maintaining, 44 Population, 7 Protein polymorphism, 44

Random drift, 21

Scalloped hazel moth, 28 Scarlet tiger moth, 3J Selection, apostatic, 42 density-dependent, 45 directional, 20 disruptive, 20 frequency-dependent, 45 gametic, 17, 45 on quantitative characters, 20 stabilizing, 20 zygotic, 17 Selective coefficient (s), 17