As in most groups of animals, important organs, such as those for propelling the blood, or for aerating it, or those for propagating the race, are found nearly uniform, they are considered as highly serviceable in classification; but in some groups of animals all these, the most important vital organs, are found to offer characters of quite subordinate value.
But it is by no means obvious, on the ordinary view, why the structure of the embryo should be more important for this purpose than that of the adult, which alone plays its full part in the economy of nature.
Instances could be given amongst plants and insects, of a group of forms, first ranked by practised naturalists as only a genus, and then raised to the rank of a sub-family or family; and this has been done, not because further research has detected important structural differences, at first overlooked, but because numerous allied species, with slightly different grades of difference, have been subsequently discovered.
Authors have insisted on the necessity of classing varieties on a natural instead of an artificial system; we are cautioned, for instance, not to class two varieties of the pine-apple together, merely because their fruit, though the most important part, happens to be nearly identical; no one puts the swedish and common turnips together, though the esculent and thickened stems are so similar.
With species in a state of nature, every naturalist has in fact brought descent into his classification; for he includes in his lowest grade, or that of a species, the two sexes; and how enormously these sometimes differ in the most important characters, is known to every naturalist: scarcely a single fact can be predicated in common of the males and hermaphrodites of certain cirripedes, when adult, and yet no one dreams of separating them.
We can understand why a species or a group of species may depart, in several of its most important characteristics, from its allies, and yet be safely classed with them.
We can understand, on these views, the very important distinction between real affinities and analogical or adaptive resemblances.
The boundaries between the great kingdom of nature, and, still more, between the various provinces, and lesser portions, into which they are subdivided, afford another illustration of the same important truth.
In revolving the causes from which these exceptions result, and applying them to the particular instances before us, we are necessarily led to two important conclusions.
4 is important. Freedom which, as I have pointed out before, Nietzsche considered a dangerous acquisition in inexperienced or unworthy hands, here receives its death-blow as a general desideratum.
So far, this is perhaps the most important paragraph.
The first ten verses, here, are reminiscent of "War and Warriors" and of "The Flies in the Market-Place." Verses 11 and 12, however, are particularly important. There is a strong argument in favour of the sharp differentiation of castes and of races (and even of sexes; see Note on Chapter XVIII.) running all through Nietzsche's writings.
THE FORMER SEEMS TO BE MUCH THE MORE IMPORTANT (The italics are mine.), for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform." Nietzsche, recognising this same truth, would ascribe practically all the importance to the "highest functionaries in the organism, in which the life-will appears as an active and formative principle," and except in certain cases (where passive organisms alone are concerned) would not give such a prominent place to the influence of environment.