Abstract

MONG factors that may produce random fluctuation of gene frequenciesA in natural populations, random sampling of gametes and random fluctuation of selection intensities may be especially important in relation to evolution.On the process of " random drift " that will be realized in finite populations due to the random sampling of gametes in reproduction, not only precise mathematical studies have been carried out (WRIGHT 1931, 1945 ; FISHER 1930 ; HALDANE 1939 ; FELLER 1950) but also several model experiments have been undertaken (cf.HOUSE 1953).Since 1931, WRIGHT has repeatedly emphasized the evolutionary significance of random drift in a natural population which is subdivided into many partially isolated sub-groups.His theory is now accepted by many evolutionists such as HALDANE (1949), MULLER (1949), DOBZHANSKY (1951) and others.On the other hand, no special attention seems to have been paid to the random fluctuation of gene frequencies due to the random fluctuation in the selection intensities until FISHER and FORD ( 1947) emphasized its prevalence in natural populations and challenged the theory of Wright by denying any significance of random drift due to small population number in evolution.This led to a polemic (cf.