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Re: Dinosaur FAQ #9



In a message dated 2/9/01 11:29:01 AM EST, mike@tecc.co.uk writes:

<< What's the difference between classification, phylogeny, systematics and 
cladistics? >>

Classification (also called "taxonomy"): setting up a system of groups and 
criteria for placing things into those groups. The system and criteria, as 
well as what you want to classify, are up to you. You can (and often do, 
subconsciously or consciously) classify stars, cars, postage stamps, 
artificial earth satellites, asteroids, geographical features, numbers, 
geometrical figures, practically anything at all. In biology, organisms are 
almost always classified by evolutionary descent: the organisms in a group 
all share a unique common ancestral organism (usually hypothetical and, we 
hope, correctly conceived), and the groups comprise "branches" and "twigs" of 
a huge hierarchy known as the Tree of Life. This classification system, 
developed during the past 250 years or so, has proved the most useful for 
biologists.

Systematics is simply the study of systems or of classification.

Phylogeny is tracing the evolution of a group of organisms. It is related to 
biological classification because some of the organisms of interest include 
those common ancestral organisms from which biological groups evolved.

Cladistics is a method for determining whether two or more organisms should 
be classified in the same group or not. Organisms are compared by their 
features or characters, and the underlying assumption is that organisms that 
share a significant number of such features/characters do so because the 
organisms evolved from a common ancestor that had those features, and not 
because they developed the features independently of one another. Just how to 
count and weigh these features/characters in order to select the useful ones 
from the noise, and thereby to construct your biological classification, 
depends the particular cladistic algorithm you use and what you already know 
or assume about the evolution of the group you're interested in.