Seite - 175 - in The Origin of Species

SPECIFIC CHARACTERS HIGHLY VARIABLE 175 mere mockery and deception ; I would almost as soon believe with the old and ignorant cosmogonists, that fossil shells had never lived, but had been created in stone so as to mock the shells living on the sea-shore. Summary.—Our ignorance of the laws of variation is pro- found. Not in one case out of a hundred can we pretend to assign any reason why this or that part has varied. But whenever we have the means of instituting a comparison, the same laws appear to have acted in producing the lesser differ- ences between varieties of the same species, and the greater differences between species of the same genus. Changed conditions generally induce mere fluctuating variability, but sometimes they cause direct and definite effects; and these may become strongly marked in the course of time, though we have not sufficient evidence on this head. Habit in pro- ducing constitutional peculiarities and use in strengthening and disuse in weakening and diminishing organs, appear in many cases to have been potent in their effects. Homologous parts tend to vary in the same manner, and homologous parts tend to cohere. Modifications in hard parts and in external parts sometimes affect softer and internal parts. When one part is largely developed, perhaps it tends to draw nourish- ment from the adjoining parts; and every part of the struc- ture v/hich can be saved without detriment will be saved. Changes of structure at an early age may aft'ect parts subse- quently developed; and many cases of correlated variation, the nature of which we are unable to understand, undoubt- edly occur. Multiple parts are variable in number and in structure, perhaps arising from such parts not having been closely specialised for any particular function, so that their modifications have not been closely checked by natural selec- tion. It follows probably from this same cause, that organic beings low in the scale are more variable than those stand- ing higher in the scale, and which have their whole organi- sation more specialised. Rudimentary organs, from being useless, are not regulated by natural selection, and hence are variable. Specific characters—that is, the characters which have come to differ since the several species of the same genus branched off from a common parent—are more vari- able than generic characters, or those which have long been