Modified Quotes - page 7
We may understand why the species of the same genus, or genera of the same family, resemble each other more nearly in their embryonic than in their more fully developed state, or how it is that in the eyes of most naturalists the structure of the embryo is even more important in classification than that of the adult, 'for the embryo is the animal in its less modified state, and in so far it reveals the structure of its progenitor. In two groups of animals, however much they may at present differ from each other in structure and habits, if they pass through the same or similar embryonic stages, we may feel assured that they have both descended from the same or nearly similar parents, and are therefore in that degree closely related. Thus community in embryonic structure reveals community of descent, however much the structure of the adult may have been modified.
Charles Lyell
Harmony thus appears as a temporary adjustment, established among all forces acting upon a given spot - a provisory adaptation; and that adjustment will only last under one condition: that of being continually modified; of representing every moment the resultant of all conflicting actions. Let but one of those forces be hampered in its action for some time and harmony disappears. Force will accumulate its effect; it must come to light, it must exercise its action, and if other forces hinder its manifestation it will not be annihilated by that, but will end by upsetting the present adjustment, by destroying harmony, in order to find a new form of equilibrium and to work to form a new adaptation. Such is the eruption of a volcano, whose imprisoned force ends by breaking the petrified lavas which hindered them to pour forth the gases, the molten lavas, and the incandescent ashes. Such, also, are the revolutions of mankind.
Peter Kropotkin