Evolution and genetics / by Thomas Hunt Morgan.

  • Thomas Hunt Morgan
Date:
1925
Catalogue details

Licence: In copyright

Credit: Evolution and genetics / by Thomas Hunt Morgan. Source: Wellcome Collection.

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    of individuals have been seen to suddenly appear. The new characters that they show are transmitted to their descendants. In some cases the new charac¬ ters depart widely from those of the stock from which the new individual has sprung; in other cases the departure may he very slight and pass unnoticed unless one is very familiar with the parent stock. In fact, it is owing, in large part, to a minute examina¬ tion of plants and animals, that many of the new characters studied by geneticists have been discov¬ ered. So small are some of the observed changes that they are not greater than the fluctuating changes due to the environment. The inheritance of the new character, when it is as slight as this, can only be determined by a careful study of successive genera¬ tions under controlled conditions both genetic and environmental. It is the realization of these require¬ ments that has enabled genetics to make its contri¬ bution to the theory of evolution. While it is true that most of these mutant changes have been observed in animals under domestication, or in species that have recently been brought into the laboratory, there is no evidence that they owe their appearance to cultivation or to domestication. On the contrary similar mutants have been found in wild species. Cultivated plants and domesticated animals are more familiar to us, and more carefully scrutinized, than are wild species. Hence in large
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