heredity seem to have resulted in too great an emphasis on the importance of 

 heredity, often at the expense of environment. It is probable that field 

 biologists, though conceding at once the importance of heredity, generally 

 are in agreement with Jennings (1925; 48): "Any characteristic requires for 

 its production both an adequate stock of chemicals and an environment adequate 

 for its production through proper interaction of these chemicals vdth one 

 another and with other things. In these senses all characteristics are 

 hereditary and all are environmental, but no characteristic is exclusively 

 hereditary or exclusively environmental." On pages 57 and 58 of this same 

 1925 publication, he says, "Heredity is stressed as all powerful; environment 

 as almost powerless; a vicious fallacy, not suoported by the results of inves- 

 tigation." 



It is clear that the study of the relation of the environment to the 

 development, structure, and habits of the living form is as well worthy of 

 critical and prolonged attention as that which has been given to heredity in 

 the past few decades. 



Influences on Snvironment 



TSa.Q environment not only influences the mammal, but the manmal (as also 

 virtually all other animals as well as plants) influences its environment 

 through its multitudinous activities, as in loosening soil by burrowing and 

 in excavating dens, burying rocks, packing soil by tramping and trail making, 

 collecting materials for nests, building dams and flooding valleys, and 

 scattering and planting seeds or destroying seeds and vegetation. Incorpora- 

 tion in the soil of organic materials, as skin, bones, flesh, and excreta, 

 also may be included in these activities. Of course, the influence of one or 

 of a few mammals ordinarily counts for little, but when the aggregate work 

 of thousands and even millions of individuals is taken into account, the effects 

 on environment are without doubt, in many instances, of great importance. The 

 soil-building and fertilizing, or even the soil-destroying, role of different 

 burrowing and terrestrial mammals remains to be determined. Christy (1884), 

 Bell (1883), and Grinnell (1923: 145) have drawn attention to the significant 

 parallel between the pocket gopher of North America and the earthworm in 

 England as regards their work in soil formation. Studies of this and related 

 subjects should be carried forward on a much broader scale than heretofore. 

 It is inevitable, in the study of life habits, that effects of mammals on 

 their surroundings should assume a prominent place (Taylor 1930, 1935a, 1935b, 

 1936) . 



Relations of Mammals and Plants 



The influence of mammals on the distribution of plants is doubtless far 

 more pervasive and important than has been realized. An intensive ecological 

 study of the vegetation of a particular area has been made by Farrow (1925) 

 in England. He writes (p. 104) : "Apparently the presence of rabbits alone 

 is sufficient to change the potentially dominant plant on Cavenham Eeath from 

 Pinus sylvestris {Scotch pinej to Pteris aquiline .brake] through a large 

 number of various stages... The passing of England from a forest period into 



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