BI'OGEN'ESIS (Gk. 1310s, hios, life alvecrit, genesis. origin. source). The doctrine that the series of forms which an animal passes through in developing from the egg to the adult is an epitome of the stages in the evolution of the species. This is stated briefly in the expres sion: Ontogeny recapitulates phylogeny. The truth of this doctrine SIM•ng to have been recog nized long ago, according to Meekel (1811), by Aristotle, Halley, Harvey. Kielemeyer. Auten reith. and many other early authors. The law is often called Von llaer's, because in his great work on the development of animals (1S26-37) he demonstrated its truth in detail. Louis Agas siz also laid stress on this law, although he (lid not accept evolution. The law is based upon ob served parallelisms between ontogenetie changes and assumed evolutionary ones. Thus. at an em bryonic stage. man possesses gill-slits and a two chambered heart, like a fish; later the gill-slits close and the heart becomes reptilian. A tail like that of lower apes is present at a later stage.
At birth the child grasps things with its feet, as the higher apes do, and not until several months after birth are the essentially animal instincts replaced by the human. To render the termi nology of the stages of ontogeny and phylogeny more precise, and at the same time comparable, the following terms have been introduced by Alpheus Hyatt: The recapitulation law remains unexplained; it does not hold in detail. but only in a rough and general way. "The embryonic record." says Balfour. "as it is usually presented to us, is both imperfect and misleading. It may be compared to an ancient manuscript with many of the sheets lost. others displaced, and with spurious passages interpolated by a later hand." See Emnarotocr; and GASTR-EA THEORY.
Abiogenesis, though apparently merely the ne gation of 'biogenesis,' has a somewhat different meaning, the term signifying reproduction by spontaneous generation—not, now accepted as a fact in any ease.