2 LIVERPOOL BIOLOGICAL SOCIETY. 
parents or ancestors than they do to other organisms. 
This is the principle of HEREDITY. 
Recognising these two important biological principles, 
breeders of cattle, dogs, pigeons, &c., are able by carefully 
selecting individuals with certain variations for breeding 
purposes, generation after generation, to produce new 
varieties or races of a very marked nature, and to mould 
their characters in almost any required direction. This is 
ARTIFICIAL SELECTION. 
Is there amongst animals in a state of nature any similar 
process of selection by which species may be modified and 
new forms produced? Charles Darwin and Alfred Russel 
Wallace, in 1858, showed that there is such a process 
at work. 
All animals and plants tend to increase so rapidly that 
if left to themselves the members of any one species would, 
in a comparatively small number of generations, cover the 
earth. Countless numbers of young are produced for which 
there is no room and no food, and which must inevitably 
die. The result of this ‘‘rate of increase”’ is that a constant 
‘‘strugele for existence’ is carried on between those 
individuals which come into competition—which live in 
the same neighbourhood, eat the same food, and are 
exposed to the same enemies. So keen and constant is 
this struggle that any advantage however slight, any 
favourable variation, may enable an individual or a set of 
individuals to get the better of the others—to survive 
when the rest are killed off. This is known as “the 
survival of the fittest,’ and is a process of “natural 
selection’’ by which particular variations are singled out 
as the individuals which survive, breed, and hand down 
their advantageous characteristics to the next generation. 
And so, just as artificial selection has produced the various 
breeds of dogs and races of pigeons, the far more searching 

