20070127

Derived

In phylogenetics, derived members of a group diverged after another member (or subgroup of members) had already diverged. The earlier members are termed basal. Neither word means anything on its own, and each can only be interpreted in the context of other members of the group.

For example:

Monocots and eudicots are derived flowering plants, having diverged from each other after palaeodicots had already split from the line.
A subgroup of great apes containing chimpanzees and gorillas is derived relative to the orangutan, which diverged earliest.

For the sake of precision, biologists often prefer "derived" over "advanced," a term which may inaccurately imply superiority. Although a derived member of a group may have higher fitness in a given environment, this is not always the case. It is quite common for both basal and derived members of a group to exist simultaneously and be well-suited for different ecological niches, or the same niche in different locations.

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