DEGENERATION THROUGH SURVIVAL OF INFERIOR INDIVIDUALS. 73 
same mutation should become the parents of two isolated colonies, it 
ought to predict that every variation occurring in either colony will 
be found in both, and in the same proportion. That this will be the 
case has not yet been shown. 
Without variation in its different forms codperating with heredity, 
isolation and selection could have no influence in guiding and shaping 
evolution. Itis, therefore, well that the mutation theory insists on the 
importance of these fundamental factors and of the laws by which 
they are controlled. But it must be remembered that through the 
powers of variation and heredity the principles of free crossing, isola- 
tion, and selection gain profound significance. These latter are the 
conditions through which the laws of the fundamental factors are 
revealed; and if we misinterpret the laws we shall fail in our explana- 
tion of the process. These laws have not been fully brought to light; 
but is there no reason to suspect that there is something lacking in 
the theory that the selection of individual variations can have no 
effect on the final result? * 
18. Degeneration of Species when the Standard of Survival is Lowered. 
The frequently observed fact that characters built up by the arti- 
ficial selection of individual variations gradually disappear when the 
selection entirely ceases seems to be the chief reason for disregarding 
the influence of such variations in the formation of varieties and 
species. But is not the same tendency seen in the characters of nat- 
ural species which the mutation theory assumes to have resulted from 
mutations? Are there not characters that have been maintained 
with unbroken constancy through countless generations of ancestors, 
not only through all the past history of the present species, but 
through the much longer history of many ancestral species, and that 
yet do not reach, in every individual of the species, the standard neces- 
sary for survival? If such individuals are able to escape the fate that 
has overtaken similarly defective ones of previous generations they 
will help to lower the standard of attainment previously gained by 
the species to which they belong. This process may be repeated in 
successive generations till the character is entirely lost. Different 
stages of such a process are revealed in the present condition of cer- 
tain species of birds, in regard to the instinct that leads the mother 
bird to sit on the eggs she lays, and to provide for the young when 

* Prof. T. H. Morgan’s position is seen in the following statement: ‘‘ Nature’s 
supreme test is survival. She makes new forms to bring them to this test through 
mutation, and does not remodel old forms through a process of individual selec- 
tion.’ See ‘Evolution and Adaptation,” p. 464. 
