See also:term for the theory according to which each living organism, however
See also:simple, arises by a
See also:process of budding, fission, spore-formation of sexual
See also:reproduction from a
See also:parent organism . Under the heading of
See also:ABIOGENESIS (q.v.) is discussed the series of steps by which the
See also:modern acceptance of biogenesis and rejection of abiogenesis has been broughtabout . No biological generalization rests on a wider series observations, or has been subjected to a more critical
See also:scrutiny than that every living organism has come into existence from a living portion or portions of a pre-existing organism . In the articles REPRODUCTION and
See also:HEREDITY the details of the relations between parent and offspring are discussed . There remains for treatment here a curious
See also:collateral issue of the theory . It is within
See also:common observation that parent and off-
See also:spring are alike: that the new organism resembles that from which it has come into existence: in
See also:fine, biogenesis is homogenesis . Every organism takes origin from a parent organism of the same kind . The conception of homogenesis, however, does not imply an absolute similarity between parent and organism . In the first place, the normal
See also:life-cycle of
See also:plants and animals exhibits what is known as alternation of generations, so that any individual in the chain may resemble its
See also:grand-parent and its grand-
See also:child, and differ markedly from its parent and child . Next, any organism may pass through a series of
See also:free-living larval stages, so that the new organism at first resembles its parent only very remotely, corresponding to an early stage in the life-
See also:history of that parent . (See
See also:EMBRYOLOGY, LARVAL FORMS and REPRODUCTION.) Finally, the conception of homogenesis does not exclude the differences between parent and offspring that continually occur, forming the material for the slow alteration of
See also:stocks in the course of
See also:evolution (see VARIATION AND SELECTION) . Homogenesis means simply that such organism comes into existence directly from a parent organism of the same
See also:race, and hence of the same
See also:species, sub-species, genus and so forth .
See also:time to time there have been observers who have maintained a belief in the opposite theory, to which the name heterogenesis has been given . According to the latter theory, the offspring of a given organism may be utterly different from itself, so that a known animal may give rise to another known animal of a different race, species, genus, or even
See also:family, or to a plant, or
See also:vice versa . The most extreme cases of this belief is the well-known
See also:fable of the "
See also:barnacle-geese," an illustrated account of which was printed in an early
See also:volume of the Royal Society of
See also:London . Buds of a particular
See also:tree growing near the
See also:sea were described as producing barnacles, and these, falling into the
See also:water, were supposed to develop into geese . The whole
See also:story was an imaginary embroidery of the facts that barnacles attach themselves to submerged
See also:timber and that a species of
See also:goose is known as the bernicle goose . In modern times the exponents of heterogenesis have limited themselves to cases of microscopic animals and plants, and in most cases, the observations that they have brought forward have been explained by minuter observation as cases of
See also:parasitism . No serious observer, acquainted with modern microscopic technical methods, has been able to confirm the explanation of their observations given by the few modern believers in heterogenesis . (P . C .
LAURENCE BINYON (1869- )
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