Heredity and sex (1913) (14594208657)

Identifier: hereditysex1913morg (find matches)
Title: Heredity and sex
Year: 1913 (1910s)
Authors: Morgan, Thomas Hunt, 1866-1945
Subjects: Heredity Sex Heredity
Publisher: New York, Columbia University Press
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School



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A BASIS FOR SELECTION The second great movement since Darwin has beento show that hereditary variations do not give a con-tinuous series but a discontinuous one. Bateson andDe Vries brought forward some twelve years ago evi-dence, in favor of this view, that has gone on increasingin volume at an amazing rate. I cannot attempt to discuss this evidence here, butI may point out the bearing of the new point of viewon the meaning of secondary sexual characters. In a number of butterflies there occur two or threeor even more different kinds of females. One of the mostremarkable cases of the kind is that of Papilio polytesthat lives in India and Ceylon. It has a single maletype and three types of females (Fig. 64). Wallace, who first observed that the three types offemale belong to one male type, argued that twoof these three types owe their origin to their resem- 126 HEREDITY AND SEX blance to butterflies of other species that are protected,namely, Papilio aristolochia and P. hector. These
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Fig. 64. — Papilio polytes; male (upper left) and three types of female(to right). The models, which two of these females are supposed tomimic, are shown to their left. two feed on the poisonous plant aristolochia and aresaid to be unpalatable. The two aberrant types ofP. polytes bearing a close resemblance to these two SECONDARY SEXUAL CHARACTERS 127 species have been dubbed the hector form and thearistolochia form. Wallace, and those who adhere to the same view,believe that the resemblance of the model and themimic has come about through the accumulation ofminute variations which have survived as a result oftheir advantages. In a word, the process of naturalselection is assumed to have gradually brought aboutthe evolution of these two new types of females. This case has been recently examined by Punnett. Punnett says that while in cabinet specimens theresemblance between the model and the mimic is re-markably close, yet in the living animals, with theirwings spread out, the resemb