An old theory which held that straight-line evolution or orthogenetic trends (see orthogenesis) might proceed to the point at which the lineage was at an adaptive disadvantage. Overspecialization was therefore considered as one of the causes of extinction. There is no reason to believe, however, that natural selection would permit evolution to proceed beyond maximum adaptation. More recently the term has been applied to highly specialized organisms which have proved incapable of responding to environmental change and so have become extinct.
Subjects: Biological Sciences.