Herbert Spencer

“ But groups severally formed of things distinguished by some common attribute which implies many other attributes, do not admit of serial arrangement. You cannot rationally say either that Historical Works should come before Biographical Works, or Biographical Works before Historical Works; nor of the sub-divisions of creative Literature, into Fiction, Poetry, and the Drama, can you give a good reason why any one should take precedence of the others.
Hence this grouping of the like and separation of the unlike which constitutes Classification, can reach its complete form only by slow steps. ”

“ Yet that differences of opinion like these arise and remain unsettled, except when they end in the establishment of sub-species, sub-genera, sub-orders, and sub-classes, sufficiently shows that the conviction is ill-based. And this is equally shown by the impossibility of obtaining any definition of the degree of difference which warrants each further elevation in the hierarchy of classes.
It is, indeed, a wholly gratuitous assumption that organisms admit of being placed in groups of equivalent values; and that these may be united into larger groups which are also of equivalent values ”

“ The structural peculiarity in which all members of one sub-kingdom differ from all members of another sub-kingdom, is a peculiarity that affects the vital actions more profoundly than does the structural peculiarity which distinguishes all members of one class from all members of another class. ”

“ As the knowledge of objects increases, it becomes possible to make groups of which the members have more numerous properties in common; and to ascertain what property, or combination of properties, is most characteristic of each group. And the classification eventually arrived at is of such kind that the objects in each group have more attributes in common with one another than they have in common with any excluded objects; one in which the groups of such groups are integrated on the same principle ”

“ If, as an alternative, this peculiar subordination of traits which organic forms display be ascribed to design, other difficulties suggest themselves. To suppose that a certain plan of organization was fixed on by a Creator for each vast and varied group, the members of which were to have many different modes of life, and that he bound himself to adhere rigidly to this plan, even in the most aberrant forms of the group where some other plan would have been more appropriate, is to ascribe a very strange motive. ”

“ If it be supposed that when magnified, each of these dots resolves itself into a cluster of clusters, representing genera and species, an approximate idea will be formed of the relations among the successively-subordinate groups constituting the animal kingdom. Besides the subordination of groups and their general distribution, some other facts are indicated. By the distances of the great divisions from the general centre, are rudely symbolized their respective degrees of divergence from the form of simple, undifferentiated organic matter; which we may regard as their common source. ”

“ Concerning the present attitude of zoologists, Prof. MacBride writes:—
"They all recognize a certain number of phyla. Each phylum includes a group of animals about whose relation to each other no one entertains a doubt. Each zoologist, however, has his own idea as to the relationship which the various phyla bear to each other. ”

“ In early attempts to arrange organisms in some systematic manner, we see at first a guidance by conspicuous and simple characters, and a tendency towards arrangement in linear order. In successively later attempts, we see more regard paid to combinations of characters which are essential but often inconspicuous, and an abandonment of a linear arrangement for an arrangement in divergent groups and re-divergent sub-groups. ”

“ When we discover that the possession of seven cervical vertebræ is a general characteristic of mammals, whether the neck be immensely long as in the giraffe, or quite rudimentary as in the whale, shall we say that though, for the whale's neck, one vertebra would have been equally good, and though, for the giraffe's neck, a dozen would probably have been better than seven, yet seven was the number adhered to in both cases, because seven was fixed upon for the mammalian type? ”

“ When, otherwise, he makes a distribution of books according to their subjects, he neglects various superficial similarities and distinctions, and groups them according to certain primary and secondary and tertiary attributes, which severally imply many other attributes—groups them so that any one volume being inspected, the general characters of all the neighbouring volumes may be inferred. He puts together in one great division all works on History ”

“ The habitual attitudes of annulose and molluscous creatures, is such that the neural centres are below the alimentary canal and the hæmal centres above. And while by these traits the annulose and molluscous types are separated from the vertebrate, they are separated from each other by this, that in the one the body is "composed of successive segments, usually provided with limbs," but in the other, the body is not segmented, "and no true articulated limbs are ever developed." ”

“ Nor, again, can any one allege that such combinations are necessary, in the sense that all other combinations are impracticable. There is not, in the nature of things, a reason why creatures covered with feathers should always have beaks: jaws carrying teeth would, in many cases, have served them equally well or better. The most general characteristic of an entire sub-kingdom, equal in extent to the Vertebrata, might have been the possession of nictitating membranes; while the internal organizations throughout this sub-kingdom might have been on many different plans. ”

“ Passing over sundry classifications in which the serial arrangement dictated by the notion of ascending complexity, is variously modified by the recognition of conspicuous anatomical facts, we come to classifications which recognize another order of facts—those of development. ”

“ The animals known as Cœlenterata are characterized in common by the possession of a part which accumulates energy more or less marked off from the part which does not accumulate energy, but only expends it; and the Hydrozoa and Actinozoa, which are sub-divisions of the Cœlenterata, are contrasted in this, that in the second these parts are much more differentiated from one another, as well as more complicated. ”

“ Though under present conditions, as above implied, it would be absurd to attempt a definite scheme of relationships, yet it has seemed to me that the adumbration of a scheme, presenting in a vague way such relationships as are generally agreed upon and leaving others indeterminate, may be ventured ”

“ Besides a completer differentiation of the organs respectively devoted to the accumulation of energy and the expenditure of energy, animals next above the Cœlenterata possess rude appliances for the transfer of energy: the peri-visceral sac, or closed cavity between the intestine and the walls of the body, serves as a reservoir of absorbed nutriment, from which the surrounding tissues take up the materials they need. ”

“ Even supposing fortuitous combinations of attributes might produce organisms that would work, we should still be without a clue to this special mode of combination. The chances would be infinity to one against organisms which possessed in common certain fundamental attributes, having also in common numerous non-essential attributes. ”

“ On observing the natures of the attributes which are common to the members of any group of the first, second, third, or fourth rank, we see that groups of the widest generality are based on characters of the greatest importance, physiologically considered ”

“ The development produces identical parts arising on both sides of an axis, growing upwards and downwards, and shutting up along two lines, so that the inner layer of the germ is inclosed below, and the upper layer above. ”