evolutionary trend A steady change in a given adaptive direction, either in an evolutionary lineage or in a particular attribute (e.g. height of shoot). Such trends are often apparent in unrelated taxa. Formerly they were attributed to orthogenesis; now orthoselection or the contending theory of species selection are invoked. See also effect hypothesis.

evolutionary trend A steady change in a given adaptive direction, either in an evolutionary lineage or in a particular attribute, e.g. height of shoot. Such trends are often apparent in unrelated taxa. Formerly they were attributed to orthogenesis; now orthoselection or the contending theory of species selection is invoked.

evolutionary trend Steady change in a given adaptive direction, either in an evolutionary lineage or in a particular attribute, e.g. dentition. Such trends are often apparent in unrelated taxa. Formerly they were attributed to orthogenesis; now ortho-selection or the contending theory of species selection are invoked.

evolutionary trend Steady change in a given adaptive direction, either in an evolutionary lineage or in a particular attribute, e.g. dentition. Such trends are often apparent in unrelated taxa. Formerly they were attributed to orthogenesis; now orthoselection or the contending theory of species selection (effect hypothesis) are invoked.