The strict phylogenetic classification of cells is unquestionably a useful procedure for specialists, regardless of whether animal individuals are distinguished from non-animal or pre-animal multicellular organisms. But for more general purposes of classification, a figurative vertical dimension of taxonomic classification, where levels of individuality are recognized, is an important discrimination. One way its importance may be appreciated is by considering that while it is said that the only classification in nature that is even approximately objective is the species, the distinction according to individuality, between animals and non-animals, is no less a natural one.
Taxonomy on the basis of the present hypothesis would be divided first of all into levels, of procaryotes (which might most consistently be regarded as molecular associations, if not societies), then of eucaryotic cells and their societies, and then of animals and their societies.
A revised taxonomy of Kingdom Animalia in terms of individuality would, admittedly, not be so orderly as one of the current trees based more or less consistently on phylogeny. Paraphyletic (partial) and polyphyletic (compound) groupings would be necessary, as super-cellular individuality has evidently developed along at least two paths, among both the protostomia (e.g., octopus) and the deuterostomia (e.g., mammals). But although it would be more complex than the current taxonomy, this proposed deviation from a more strict systematics would not actually be an unconventional procedure. The Eucaryotes already form a polyphyletic group in taxonomy if, as it is maintained, they ascend from the association of bacteria and archaea (Woese 1990). And the conventional paraphyletic discrimination of mammals and birds from Reptlia is based on little more than custom and convenience – and perhaps a little mammalian vanity.
In seeking to accommodate individuality to systematic taxonomy it seems clear that animals, defined as individual super-cellular organisms, would not be a monophyletic group (of single descent), unless the present phylogeny is seriously in error and the cephalic bilaterals (including both octopus and mammals) are more closely related than all those that are non-cephalic. Although all animals thus defined are bilaterals, not all protostomia and not all deuterostomia (as they are currently classified) are animals. It seems reasonable therefore to rename the Kingdom Animalia as the Metazoa, redefining Animalia as a polyphyletic sub-kingdom of Metazoa, perhaps renamed as the Euanimalia. The excluded members of the present taxon of Animalia, those without actual brains, could accordingly constitute the paraphyletic sister sub-kingdom Proanimalia.
The division of metazoans into the sub-kingdoms Proanimalia and Animalia may be unsatisfactory from a strictly phylogenetic point of view, requiring as it would the introduction of paraphyletic and polyphyletic groups. But from a recognition of the differences among cells, cellular societies, and individuals, the revision is essential and indispensable to a better understanding of individuality as a natural phenomenon, and to an orientation toward concentrated research into the specific characteristics of cellular societies and individualities.
8. Conclusion
Current taxonomy has been described as a largely indiscriminate classification of cells, their societies, and their larger individualities, any of which may be found to be treated, by convention, as individual organisms. It has been hypothesized that in the biotic cell, and in the true animal, nature has constituted itself into wholes, into individualities, by means of the development of integrative structures. Individuality has been presented as a most significant feature of nature, for which proper accommodation should be made in a revised taxonomic system.
If oak trees and jellyfish are to be recognized as non-individuals, as vast cellular societies, and if the distinctiveness of individuality is to be fully appreciated, in cells and in animals, taxonomy may contribute to an enlightening and exciting reordering of the way we view ourselves and the life forms around us.
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