ANIMAL LIFE. 515 



fctarting on a downward path to extinction or an upward path to dom- 

 ination, a wanton sacrifice of rich legacies of structure or improvement 

 of such as may be possessed? 



While adaptations and progressive modifications have been the rule, 

 there are a few striking exceptions, and we can not assert that preserva- 

 tion of a particular plane of development is impossible. Picture the 

 little lamp shell, Lingula, living on unaltered from age to age, its fos- 

 sils being found away back in the earliest Paleozoic time and in sub- 

 sequent ages up to the present day — so much for staying at home and 

 attending strictly to its own business. True no change — no progress — 

 but as an example of the staying qualities nothing can be more striking. 



Concluding, then, we may look in wide view at life as originating in 

 most favorable conditions of moisture and temperature ; as pushing out 

 to occupy all favorable environments, and then, from the congestion of 

 life in such places, as pushing out to extremes in various directions and, 

 ultimately, by a process inherent in life itself, constantly but imcon- 

 sciously striving to occupy every available niche having the remotest 

 possible opportunities for the support of organic beings. The animal 

 choosing its environment and the environment reacting to modify the 

 structure of the animal. 



But this pushing has been along different lines and some of these 

 involve no such radical change of form or habit as to restrict the ani- 

 mal to a special environment. In such broad highways progressive 

 evolution is still possible, and we may expect future modification, 

 advancement, adaptation, the height to which advancement is possible 

 depending on how fully the animal may preserve its general varied 

 structure while reaching such perfection of organs as to enable it to 

 dominate the forms with which it must compete for mastery. 



Where the road narrows and the animal in traversing it is obliged 

 to sacrifice some portion of its structure and to adopt some restriction 

 of habit the result is a limitation which must ultimately mean a bar to 

 all progressive evolution in the acceptance of a particular limited sphere 

 within which it may survive, but to leave which means extinction. 

 Adaptation to sedentary life, parasitism, desert, cave, deep sea, polar 

 frigidity or extreme heat is to shut the door of progress and give over 

 to mere survival. 



We may be tempted to moralize a little, for a moment's thought 

 assures us that man himself is, like other animals, subject to these 

 inevitable laws, and that retrogression, degeneration, decay and exter- 

 mination are as possible to him or to certain of his races as to any 

 other form of life, but this subject widens into the great new field of 

 sociology — one of the latest, richest and most important of the 

 branches of biology. 



