370 Appendix 
and physical conditions that obtained in the primordial 
environment when life first appeared on earth.® 
But it is easily seen that our theory is limited to a 
consideration of the tendency to invariability only so far 
as it manifests itself each moment in the behavior of 
each individual. Therefore instead of serving as a 
far too one-sided starting point for the explanation of 
the evolution of species it forms the basis upon which 
all the most important affective tendencies of the animal 
world may be built up. . 
As a factor of invariability for the individual, this 
tendency to preserve its stationary physiological condi- 
tion is indeed one of the most important factors in the 
variation and progress of the species, but in quite a 
different way from that pointed out by Quinton. For 
from this tendency arose and developed the power of 
motion which is the greatest difference between plants 
and animals, and with which also has kept pace the 
development and perfection of the whole motor ap- 
paratus, including that of the nerves and senses, which 
plays so important a part in determining the character- 
istics which distinguish the different zoological species. 
Finally as a factor of individual invariability it has 
proved by its effect on man to be one of the most con- 
spicuous factors in all social evolution, for we may 
well say that technical inventions and industrial products 
from the first cave dwellings, the first skins used for 
clothing, the first discovery of fire to the most complex 
attainments of to-day have tended constantly more or 
less directly or indirectly towards one single goal, 
®R. Quinton, L’eau de mer, milieu organique. Especially Book 
II, “Loi générale de constance originelle,” pp. 429-456. Paris, Mas- 
son, 1904. 
