The Making of Species 
It is thus conceivable that, in a brood consist- 
ing of several individuals, a particular molecule 
or set of molecules in one of the individuals may 
receive more than its share of nourishment, and 
this will result in the organs of that individual 
which spring from the well-nourished molecules 
being exceptionally well developed. Thus arises 
the phenomenon of differences between the 
members of a litter or brood. 
Natural selection will tend to eliminate those 
individuals in which the resulting variation is an 
unfavourable one. If the environment is such, 
as in the case of an internal parasite, that the 
production of germ cells is the most necessary 
function of the organism, then those individuals 
in which the germ-forming molecules increase at 
the expense of the body-forming ones will tend 
to be preserved. This would cause the pheno- 
menon which biologists term degeneration. 
The nourishment of the various biological 
molecules may possibly depend on their relative 
positions in the egg. Those in a favourable 
position will then tend to develop at the expense 
of the others, This will result in variation along 
definite lines. Each succeeding generation will 
tend to an increased development of that par- 
ticular organ to which the favourably-situated 
molecule gives rise. This process may continue, 
as in the case of the horns of the Irish elk, until 
the development of that particular organ becomes 
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