The study of classification is called taxonomy, but there are many ways of dividing up an existing group of living things, depending on the assumptions made.
Living things can be sub-divided according to similarities, but the end result will depend on which similarities are studied and taken into account.
John Ray published a study of Cambridge plants in 1660, setting a new standard for descriptive work in botany that would influence his successors.
Around 1700, while working at the Jardin des Plantes, Joseph Pitton de Tournefort developed the idea of a genus that Linnaeus would later seize on with delight.
In 1753 Linnaeus published his Species Plantarum, which marked the beginning of what we now see as the standard modern binomial (genus and species) plant names.
In 1758 Carl von Linné ( Linnaeus ) published the tenth edition of his Systema Naturae. Modern binomial zoological names for animals began at this point.
In 1766 Buffon suggested that each Linnaean genus stemmed from a single ancestor. This was part of Buffon's theory that all evolution was degeneration.
Linnaeus did not like the Comte de Buffon and his ideas at all, and took advantage of this, as the chief namer of things, to call a stinky weed Buffonia.
The common five kingdom classification of living organisms is Monera, Protista, Fungi, Plantae and Animalia. In this system, the Archaea lie in the Monera.
The highest level of classification is generally taken as the kingdom, and in that system, the level below the kingdom is a phylum.
A species is defined as a group of organisms that share a common gene pool and breed together, or could do so, if they were in the same place at the same time.
Another definition of a species regards them as a group of organisms which share in a common gene pool. This leaves isolated populations as a problem.
Every species is named according to the rules of binomial nomenclature, with a unique genus name and a species name that is unique within that genus.
The sub-divisions of living things are assumed to reflect their history in evolution fairly closely, but there will always be some argument around the edges of this.
All sorts of data may be used in arriving at a classification system, including genomics, biochemistry and structure, and these may lead to conflicting results.
In a few cases, convergent evolution may produce similar organisms and trick scientists into grouping unrelated organisms together, based on similar appearance.
In a few cases, the effects of adaptive radiation may lead to rapid change and trick scientists into separating related organisms because they look different.
One way to avoid confusion caused by misleading appearances is to use genomic evidence, but horizontal gene transfer can interfere with this form of evidence.
One popular form but somewhat radical form of taxonomy is called the cladistic method, another popular form of taxonomy is called the phenetic method.
Some groups are suspected of being polyphyletic: the bats, for example, are composed of two groups, and some scientists think these evolved separately.
Having a group called 'invertebrate' shows us an unnatural division of living things, as about all they have in common is the lack of a backbone or notochord.
Mammals are often grouped by their dental formula, the numbers of incisors, canines, premolars and molars in their jaws. This usually matches other evidence.
In 1842, Johannes Müller rediscovered and confirmed something that Aristotle knew: that dogfish young can have a placenta-like attachment to the mother.
This file is http://members.ozemail.com.au/~macinnis/scifun/splatsclassify.htm, first created on February 16, 2008. Last recorded revision (well I get lazy and forget sometimes!) was on February 16, 2008.