orthogenesis Evolutionary trends that remain fairly constant over long periods of time and so appear to lead directly from ancestor organisms to their descendants. This was once explained as the result of some internal directing force or ‘need’ within the organisms themselves. Such metaphysical interpretations have been displaced by the concepts of orthoselection and species selection. See also aristogenesis; entelechy; and nomogenesis.

orthogenesis Evolutionary trends that remain fairly constant over long periods of time and so appear to lead directly from ancestor organisms to their descendants. This was once explained as the result of some internal directing force or ‘need’ within the organisms themselves. Such metaphysical interpretations have been displaced by the concepts of orthoselection and species selection. See also ARISTOGENESIS; ENTELECHY; NOMOGENESIS.

orthogenesis Evolutionary trends that remain fairly constant over long periods of time and so appear to lead directly from ancestor organisms to their descendants. This was once explained as the result of some internal directing force or ‘need’ within the organisms themselves. Such metaphysical interpretations have been displaced by the concepts of orthoselection and species selection.

orthogenesis Evolutionary trends that remain fairly constant over long periods of time and so appear to lead directly from ancestor organisms to their descendants. This was once explained as the result of some internal directing force or ‘need’ within the organisms themselves. Such metaphysical interpretations have been displaced by the concepts of orthoselection and species selection.

orthogenesis An early theory of the nature of evolutionary change, which proposed that organisms evolve along particular paths predetermined by some factor in their genetic make-up. More recent understanding of selection pressure and other external forces that can be shown experimentally to affect the survival of organisms has proved the improbability of the theory.