Chav ER Wid 
ORIGIN OF ADAPTATIONS AND OF SPECIES 
I. ADAPTATIONS 
Organic Evolution.—Organic evolution is essentially the 
evolution of adaptive structures and functions. There remain 
to be explained, however, non-adaptive structures and func- 
tions, and no theory of evolution 1s adequate which does not 
account for the useless as well as the useful characters. 
Existing structures are due to the nature of the organism 
and the nature of the environment; in other words, are results 
of the activity of protoplasm under the influence of environ- 
mental forces. Variations arise which are useful or not and 
either transmissible or not. Useful transmissible variations 
not only remain but tend to become more nearly perfect ; while 
useless variations tend to disappear. 
The various theories of organic evolution differ chiefly in 
their answers to these questions: (1) What is the nature of 
variations and how do they arise? Variations are classed as 
either continuous or discontinuous; adaptive or unadaptive. 
In asexual organisms, variations are brought about by the 
direct influence of temperature, light and other primary fac- 
tors upon protoplasm; in sexual organisms, variations are due 
to another cause as well, namely, the union of two kinds of 
protoplasm. In any given case of variation, how much is due 
immediately to protoplasm and how much to the environment ? 
(2) What kinds of variations are transmissible? Discontinu- 
ous variations (sports) are strongly transmissible as a rule, 
while continuous (individual) variations are often non-trans- 
missible; though it is often difficult to decide whether they are 
transmissible or not. Each kind of variation has to be exam- 
ined separately, on its own merits. Difficulties arise from the 
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