Dictionary of Human Evolution and Biology

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Phylogenetic Constraint

Trait that developed in the history of a taxon that lead that group in a direction from which it cannot then change; e.g. after the los of a particular structure. For example, panda ancestors lost the cecum, which in other animals is used for the fermentation of fibrous foods. Their descendants today need to process large amounts of fiber, but do not have the morphological structures to digest it efficiently, and consequently are constrained to consume an extraordinarily large amount of bamboo in order to survive only off the soluble components. A factor of historicity.

See contingency.

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