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Evolution__3rd_Edition

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16Classification and <strong>Evolution</strong><br />

B iological classification is concerned with distinguishing<br />

and describing living and fossil species, and with<br />

arranging those species into a hierarchical, multilevel<br />

classification. The theory of evolution has a strong influence<br />

on classificatory procedures. Chapter 13 was about species;<br />

this chapter is about classification above the species level.<br />

We begin by looking at the two principles a phenetic and<br />

phylogenetic a that have been used to classify species<br />

hierarchically into groups (such as genera, families, and<br />

higher level categories), and see how the three main schools<br />

of biological classification put them to use. We then look at<br />

the conditions in which the two principles give the same, or<br />

differing, classifications of a set of species. The main question<br />

of the chapter is which (if any) of the two principles is the<br />

better justified. The answer comes from an argument that<br />

phylogenetic classification at its best is objective, whereas<br />

phenetic classification always suffers from subjectivity.<br />

We then look at some consequences of the strict use of<br />

phylogenetic relations to classify species into groups.<br />

We finish by considering why real evolution has resulted<br />

in a tree-like diverging pattern of relations among species.

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