Page:Popular Science Monthly Volume 63.djvu/232

228 Mendel's laws are of much practical importance because they make plain to breeders of economic plants and animals that they can not do what has been attempted so frequently, make improved breeds by combining the divergent characters of close-bred varieties. The Mendelian facts are of general evolutionary interest, not because they explain descent, but because they are incompatible with the commonly accepted static theories of development which hold that evolutionary progress is due to external or environmental influences and overlook the independent self-caused motion of species. More detailed presentation of the latter view can not be undertaken here; it must suffice for the present to have pointed out that cytology has not proved the universality of Mendel's laws as 'principles of inheritance,' nor do the laws prove that the chromosomes are the long-sought 'hereditary mechanisms.'

Heredity should be thought of as a general property of organisms, and not as the function of a special organ of the cell or of the embryo. As a phenomenon it should be associated with crystallization, on the one side, and with memory, on the other. There may be simpler properties of matter which render crystallization, heredity and memory possible, but such properties are not yet recognized in physics and chemistry, so that the terms and theories of these sciences are of little use in the discussion of evolution.

Viewed as the basis of an independent generalization the Mendelian experiments ran counter to multitudes of the most obvious and best established data of biology, and it may have been on this account that they were so long disregarded. The apparent conflict is here explained as due to erroneous theories of evolution; the recognition of spontaneous organic motion enables Mendel's facts to find a place in the evolutionary series, and renders the general inferences of de Vries, Bateson and Wilson unnecessary. Nor need the present view be thought to depreciate the importance of Mendel's laws, since such discoveries are of much greater practical value after they have found their true place among related facts than while as novelties they are permitted to obscure all the adjoining fields of investigation.