The Principles of Biology, Volume 1 · Herbert Spencer
CLASSIFICATION.
Between these two modes of classification note the essential distinctions. Arrangement according to any single conspicuous attribute is comparatively easy, and is the first that suggests itself: a child may place books in the order of their sizes, or according to the styles of their bindings. But arrangement according to combinations of attributes which, though fundamental, are not conspicuous, requires analysis; and does not suggest itself till analysis has made some progress. Even when aided by the information which the author gives on his title page, it requires considerable knowledge to classify rightly an essay on Polarization; and in the absence of a title page it requires much more knowledge. Again, classification by a single attribute, which the objects possess in different degrees, may be more or less serial, or linear. Books may be put in the order of their dates, in single file; or if they are grouped as works in one volume, works in two volumes, works in three volumes, &c., the groups may be placed in an ascending succession. 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. I have shown (_Essays_, Vol. II., pp. 145-7) that, other things equal, the relations among phenomena are recognized in the order of their conspicuousness; and that, other things equal, they are recognized in the order of their simplicity. The first classifications are sure, therefore, to be groupings of objects which resemble one another in external or easily-perceived attributes, and attributes that are not of complex characters. Those likenesses among things which are due to their possession in common of simple obvious properties, may or may not coexist with further likenesses among them. When geometrical figures are classed as curvilinear and rectilinear, or when the rectilinear are divided into trilateral, quadrilateral, &c., the distinctions made connote various other distinctions with which they are necessarily bound up; but if liquids be classed according to their visible characters--if water, alcohol, sulphuret of carbon, &c., be grouped as colourless and transparent, we have things placed together which are unlike in their essential natures. Thus, where the objects classed have numerous attributes, the probabilities are that the early classifications, based on simple and manifest attributes, unite under the same head many objects that have no resemblance in the majority of their attributes.
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; and one in which the degrees of differentiation and integration are proportioned to the degrees of intrinsic unlikeness and likeness. And this ultimate classification, while it serves to identify the things completely, serves also to express the greatest amount of knowledge concerning the things--enables us to predicate the greatest number of facts about each thing; and by so doing implies the most precise correspondence between our conceptions and the realities. § 99. Biological classifications illustrate well these phases through which classifications in general pass. 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.
Plants are either Flowerless, or Flowering; and these are Dicotyledones, or Monocotyledones. Among the minor groups which he placed under these general heads, "were Fungi, Mosses, Ferns, Composites, Cichoraceæ, Umbellifers, Papilionaceous plants, Conifers, Labiates, &c., under other names, but with limits not very different from those now assigned to them." Being much in advance of his age, Ray's ideas remained dormant until the time of Jussieu; by whom they were developed into what has become known as the Natural System: a system subsequently improved by De Candolle. Passing through various modifications in the hands of successive botanists, the Natural System is now represented by the following form, which is based upon the table of contents prefixed to Vol. II. of Prof. Oliver's translation of the _Natural History of Plants_, by Prof. Kerner. His first division, Myxothallophyta (= Myxomycetes), I have ventured to omit. The territory it occupies is in dispute between zoologists and botanists, and as I have included the group in the zoological classification, agreeing that its traits are more animal than vegetal, I cannot also include it in the botanical classification. Here, linear arrangement has disappeared: there is a breaking up into groups and sub-groups and sub-sub-groups, which do not admit of being placed in serial order, but only in divergent and re-divergent order. Were there space to exhibit the way in which the Alliances are subdivided into Orders, and these into Genera, and these into Species, the same principle of co-ordination would be still further manifested.
PHYLA. CLASSES. ALLIANCES. SUB-PHYLA. SUB-CLASSES. THALLOPHYTA I. Schizophyta 2. Cyanophyceæ. Blue-green Algæ. 3. Schizomycetes. II. Dinoflagellata Peridineæ 4. III. Bacillariales 5. IV. Gamophyceæ I. Chlorophyceæ 6. Protococcoideæ. 7. Siphoneæ. 8. Confervoideæ. 9. Conjugatæ. 10. Charales. 11. Phæophyceæ. 12. Dictyotales. 13. Florideæ, Red Seaweeds. V. Fungi I. Phycomycetes 14. Oomycetes. 15. Zygomycetes. II. Mesomycetes 16. 17. III. Mycomycetes 18. 19. Additional group of Fungi, Lichenes. ARCHEGONIATÆ I. Bryophyta 20. Hepaticæ, Liverworts. 21. Musci, Mosses. II. Pteridophyta Vas. Cryptogams 22. Filices, Ferns. 23. Hydropterides, Rhizocarps. 24. Equisetales, Horse-tails. 25. Lycopodiales, Club-mosses. PHANEROGAMIA (Flowering Plants.) GYMNOSPERMÆ I. Cycadales, Cycads 26. II. Coniferæ 27. III. Gnetales 28. ANGIOSPERMÆ I. Monocotyledons 29. Liliifloræ. 30. Scitamineæ. 31. Gynandræ. 32. Fluviales. 33. Spadicifloræ. 34. Glumifloræ. II. Dicotyledons I. Monochlamydæ 35. Centrospermæ. 36. Protiales. 37. Daphnales. 38. Santalales. 39. Rafflesiales. 40. Asarales. 41. Euphorbiales. 42. Podostemales. 43. Viridifloræ. 44. Amentales. 45. Balanophorales. II. Monopetalæ 46. Caprifoliales. 47. Asterales. 48. Campanales. 49. Ericales. 50. Vaccinales. 51. Primulales. 52. Tubifloræ. III. Polypetalæ 53. Ranales. 54. Parietales. 55. Malvales. 56. Discifloræ. 57. Crateranthæ. 58. Myrtales. 59. Melastomales. 60. Lythrales. 61. Hygrobiæ. 62. Passifloræ. 63. Pepones. 64. Cactales. 65. Ficoidales. 66. Umbellales. On studying the definitions of these primary, secondary, and tertiary classes, it will be found that the largest are marked off from one another by some attribute which connotes sundry other attributes; that each of the smaller classes comprehended in one of these largest classes, is marked off in a similar way from the other smaller classes bound up with it; and that so, each successively smaller class has an increased number of co-existing attributes.
The classification of Cuvier, based on internal organization instead of external appearance, was a great advance. He asserted that there are four principal forms, or four general plans, on which animals are constructed; and, in pursuance of this assertion, he drew out the following scheme. First Branch. ANIMALIA VERTEBRATA. Cl. 1. Mammalia. Cl. 2. Birds. Cl. 3. Reptilia. Cl. 4. Fishes. Second Branch. ANIMALIA MOLLUSCA. Cl. 1. Cephalapoda. Cl. 2. Pteropoda. Cl. 3. Gasteropoda. Cl. 4. Acephala. Cl. 5. Brachiopoda. Cl. 6. Cirrhopoda. Third Branch. ANIMALIA ARTICULATA. Cl. 1. Annelides. Cl. 2. Crustacea. Cl. 3. Arachnides. Cl. 4. Insects. Fourth Branch. ANIMALIA RADIATA. Cl. 1. Echinoderms. Cl. 2. Intestinal Worms. Cl. 3. Acalephæ. Cl. 4. Polypi. Cl. 5. Infusoria. But though Cuvier emancipated himself from the conception of a serial progression throughout the Animal Kingdom, sundry of his contemporaries and successors remained fettered by the old error. Less regardful of the differently-combined sets of attributes distinguishing the different sub-kingdoms, and swayed by the belief in a progressive development which was erroneously supposed to imply a linear arrangement of animals, they persisted in thrusting organic forms into a quite unnatural order. The following classification of Lamarck illustrates this.
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