64 FOOT-NOTES TO EVOLUTION. 
result of common descent. The differences are due to 
various influences, chief among these being competition 
in the struggle for existence between individuals and 
between species, whereby those best adapted to their 
surroundings live and reproduce their kind. 
This theory is now the central axis of all biological 
investigation in all its branches, from ethics to histology, 
from anthropology to bacteriology. In the light of this 
theory every peculiarity of structure, every character or 
quality of individual or species, has a meaning and a 
cause. It is the work of the investigator to find this 
meaning as well as to record the fact. “One of the 
noblest lessons left to the world” by Darwin, Frank 
Cramer says, “is this, which to him amounted to a pro- 
found, almost religious, conviction, that 
every fact in Nature, no matter how in- 
significant, every stripe of colour, every 
tint of flowers, the length of an orchid’s nectary, un- 
usual height in a: plant, all the infinite variety of appar- 
ently insignificant things, is full of significance. For 
him it was an historical record, the revelation of a cause, 
_ the lurking place of a principle.” 
, According to the theory of evolution every structure 
of to-day finds its meaning in some condition of the 
past. The inside of an animal tells what it really is, for 
it bears the record of heredity. The outside of an ani- 
mal tells where its ancestors have been, for it bears 
record of concessions to environment, Similarity in 
essential structure is known as homology. By the theory 
of evolution homology, wherever it is found, is proof of 
blood relationship. 
The theory of organic evolution through natural 
law was first placed on a stable footing by the observa- 
tions and inductions of Darwin. It has therefore been 
long known as Darwinism, although that term has been 
Each fact has a 
meaning. 
