Adaptation 65 
would remain a great deal that could not be referred to selection; 
but we are postulating an evolution which has stretched back through 
aeons, and in the course of which innumerable adaptations took place, 
which had not merely ephemeral persistence in a genus, a family or 
a class, but which was continued into whole Phyla of animals, with 
continual fresh adaptations to the special conditions of each species, 
family, or class, yet with persistence of the fundamental elements. 
Thus the feather, once acquired, persisted in all birds, and the 
vertebral column, once gained by adaptation in the lowest forms, 
has persisted in all the Vertebrates, from Amphioxus upwards, 
although with constant readaptation to the conditions of each par- 
ticular group. Thus everything we can see in animals is adaptation, 
whether of to-day, or of yesterday, or of ages long gone by; every 
kind of cell, whether glandular, muscular, nervous, epidermic, or 
skeletal, is adapted to absolutely definite and specific functions, 
and every organ which is composed of these different kinds of cells 
contains them in the proper proportions, and in the particular 
arrangement which best serves the function of the organ; it is thus 
adapted to its function. 
All parts of the organism are tuned to one another, that is, they 
are adapted to one another, and in the same way the organism as a 
whole is adapted to the conditions of its life, and it is so at every 
stage of its evolution. 
But all adaptations can be referred to selection; the only 
point that remains doubtful is whether they all must be referred 
to ix. 
However that may be, whether the Lamarckian principle is 
a factor that has cooperated with selection in evolution, or whether 
it is altogether fallacious, the fact remains, that selection is the cause 
of a great part of the phyletic evolution of organisms on our earth. 
Those who agree with me in rejecting the Lamarckian principle 
will regard selection as the only guzding factor in evolution, which 
creates what is new out of the transmissible variations, by ordering 
and arranging these, selecting them in relation to their number and 
size, as the architect does his building-stones so that a particular 
style must result, But the building-stones themselves, the variations, 
have their basis in the influences which cause variation in those vital 
units which are handed on from one generation to another, whether, 
taken together they form the whole organism, as in Bacteria and 
other low forms of life, or only a germ-substance, as in unicellular 
and multicellular organisms’. 
1 Variation under Domestication, 1875, 1. pp. 426, 427. 
2 The Author and Editor are indebted to Professor Poulton for kindly assisting in the 
revision of the proof of this Essay. 
D. 5 
