Catalogue of Fossil Birds Pierce Brodkorb

this is due to the superiority of the heterozygotes then the polymorphism is still not proved to be adaptive--in fact it may be regarded as the opposite, since what is wanted is a pure population of heterozygotes and the homozygotes are merely poorly adapted individuals that are automatically produced but are not wanted.It is frequently stated that the different morphs in Drosophila are adapted to different sub-niches and Mayr seems to accept this idea.Certainly, if different morphs did different things which other morphs could not do, the population would in this sense be better adapted the more morphs it had and would exploit the environment more completely.A good example would be those polymorphic mimetic butterflies in which different morphs mimic different distasteful models; presumably the addition of a new morph to a population would mean an increase in total population size and a better exploitation of the available distasteful properties of the models.Such a situation has never yet been shown to occur in Drosophila although it is usually stated, as here, to be the reason for the adaptivehess of polymorphism.In general, however, Mayr's treatment of the vast variety of subjects relating to speciation is exceedingly careful and fair.No author can satisfy everyone in his expositions and even where one disagrees with them one cannot ignore Mayr's summaries and arguments on particular topics.One must congratulate him on so wide ranging, thorough, and stimulating a presentation of the most important single process in evolution.•ARx•XURJ. CA•.