Systematics

Systematics - a definition

Systematics is the branch of biology that deals with classifying living beings: the diversity and interrelationships of living beings, both current organisms ("neontology") and prehistoric ones ("palaeontology").  It can be divided into three parts.

• Taxonomy - the describing and naming new taxa (a taxon is any specifically defined group of organisms).  Taxonomic groups are used to categorize similar taxa for identification-like  field guides. These do not necessarily represent evolutionary trends. Smaller taxonomic groups used to relate organisms at greater levels of similarities.

• Classification - the organization of information about diversity arranging them into a convenient, formal classification into a hierarchical system, and providing means of identifying them (e.g., diagnostic keys). [see e.g. the Linnean system]

• Phylogeny - determination of the ancestral relationships of organisms, and the group's evolutionary history through time.  Phylogenetics is the field of biology concerned with identifying and understanding the evolutionary relationships between the many different kinds of life on earth.

Systematics - history

Symbolic Correspondences

In pre-modern cultures, the world (including living organisms and inanimate objects) was classified according to the archetypal mandala - the four cardinal points, each associated with an element, a season, a deity, an animal, and so on, which constituted the underlying structure of the world (much as the elementary particles and forces in quantum physics is considered nowadays).  This system of  symbolic correspondences by association, which is metaphysical rather than scientific,  reached great sophistication in the Chinese system of  Five States of Change, the traditional Indian (Samkhyan and Tantric) doctrine of  tattwas, and more recently (late 19th century) in  Hermetic Kabbalah, as well as in "New Age" thought in general.

The Scala Natura

A different slant on things was given by  Aristotle, who introduced the idea of the scala natura - the ladder of nature - according to which the natural world is interpreted in terms of the principle of plenitude, the overflowing abundance of the first principle or Godhead which creates successive beings.  The further the beings are from the source the more ontologically impoverished they are.  So you have formless matter right at the bottom, then rocks, plants, lower animals, higher animals, man, and finally spiritual and divine beings.  This hierarchical view of the world - the  Great Chain of Being [see Arthur Lovejoy's classic coverage of this topic], persisted through the middle ages and up until the scientific revolution of the seventeenth and eighteenth centuries, when it was replaced by a sort of  monotheistic dualism - there is the material world or creation, and there is God in his heaven.

Aristotle and the dawn of science

Though Aristotle's work in zoology was not without errors, it was the greatest biological synthesis of the time, and remained the ultimate authority for many centuries after his death.  Animals could be classified by their way of life, their actions, or by their parts.  His observations on the anatomy of octopus, cuttlefish, crustaceans, and many other marine invertebrates are remarkably accurate, and could only have been made from first-hand experience with dissection. Aristotle described the embryological development of a chick; he distinguished whales and dolphins from fish; he described the chambered stomachs of ruminants and the social organization of bees; he noticed that some sharks give birth to live young -- his books on animals are filled with such observations, some of which were not confirmed until many centuries later.

Aristotle's classification of animals grouped together animals with similar characters into genera (used in a much broader sense than the current Linnean definition) and then distinguished the species within the genera. He divided the animals into two types: those with blood, and those without blood (or at least without red blood). These distinctions correspond closely to our distinction between vertebrates and invertebrates. The blooded animals, corresponding to the vertebrates, included five genera: viviparous quadrupeds (mammals), birds, oviparous quadrupeds (reptiles and amphibians), fishes, and whales (which Aristotle did not realize were mammals).  This basic division (except for the whales) was to be adopted by Linneus (for whom the "genera" became classes). The bloodless animals were classified as cephalopods (such as the octopus); crustaceans; insects (which included the spiders, scorpions, and centipedes, in addition to what we now define as insects); shelled animals (such as most molluscs and echinoderms); and "zoophytes," or "plant-animals," (e.g. corals) which supposedly resembled plants in their form.

The Linnean System

In the 18th century the Swedish botanist Carl von Linne, better known under the Latinized form of his name, Linnaeus, developed what's known as the binomial system of classification, in order to simplify the chaotic state of affairs around at his time.  (Some plants were given names ten words long for example).  He used Latin because that was the academic language of the time.  The modern system of classification in current widespread use is the binomial hierarchical system introduced by Linnaeus.

The Linnean system

The Darwinian Revolution

While Linneus founded taxonomy and classification, it was left to Charles Darwin in the 19th century to introduce the theory of evolution and hence make possible phylogenetic reconstruction; that is, the evolutionary relationships and history of the various groups of organisms through geological time (millions of years).  That's where things really get interesting, because life as a dynamic process is much more fascinating than life as a static series of unchanging types.

Evolutionary Systematics

"Vertical" and "Horizontal" Classification

The Cladistic revolution

Over the last few decades there has been a major paradigm shift in biology and systematics, with the Linnean system being pretty much superseded by the cladistic one.  Cladistics is based not on morphological similarity (as in the Linnean system) but on ancestor and descent relationship (phylogeny).

Cladistics

Proceedings of a Mini-Symposium on Biological Nomenclature in the 21st Century - suggests replacing the Linnean system with a cladistic phylogenetic system of nomenclature.  However R. K. Brummitt in Quite Happy with the Present Code, Thank You - argues against the tendency to reduce the Linnean system to the Cladistic one by eliminating paraphyletic taxa.

Dinosaurs and Evolution part 4 - by Jeff Polling, Points out weaknesses of the Linnean scheme and argues for the cladistic, with reference to Mononykus, a prehistoric animal that, like Archaeopteryx, was transitional between dinosaurs and birds (note: this page is part of a longer discussion regarding evolution and creationism)

Phylogenetics Databases and Information

It should be pointed out here that - as with fields of  science in general - all of these biotic classification schemes are in a sense arbitrary, dependent on the incomplete state of knowledge at present.   Systematic classifications are supposed to convey phylogenetic information according to ancestry and descent, as well as being names for organisms or groups of organisms.  But there still is (and perhaps never will be) a complete consensus on the phylogenetic relationships of organisms on Earth.  As research progresses, phylogenetic concepts change, and the names that are tied to these concepts change as well. Research also discovers numerous instances of wrongly applied labels, such as when two or more species are found hiding under a single species name, and identifies previously undescribed creatures and lineages for which new names are needed.

[note - part of above paragraph from  About Protist Image Data]

Taxonomy: Classifying Life - John Kimball - excellent overview (part of Kimball's Biology Pages)

Taxonomy, Transitional Forms, and the Fossil Record - Keith B. Miller - online essay, makes some interesting observations

Biological Systematics : Principles and Applications
by Randall T. Schuh