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The Variation of Animals and Plants

Chapter XIII: Inheritance – continued
DIFFERENT FORMS OF REVERSION — IN PURE OR UNCROSSED BREEDS, AS IN
PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS — REVERSION
IN FERAL ANIMALS AND PLANTS — REVERSION IN CROSSED VARIETIES AND SPECIES —
REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR
FRUIT — IN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL — THE ACT OF
CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS —
OTHER PROXIMATE CAUSES OF REVERSION — LATENT CHARACTERS — SECONDARY
SEXUAL CHARACTERS — UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY —
APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS — THE
GERM, WITH ALL ITS LATENT CHARACTERS, A WONDERFUL OBJECT — MONSTROSITIES
— PELORIC FLOWERS DUE IN SOME CASES TO REVERSION.
The great principle of inheritance to be discussed in this chapter has been recognised by
agriculturists and authors of various nations, as shown by the scientific term Atavism,
derived from atavus, an ancestor; by the English terms of Reversion, or Throwing-back;
by the French Pas-en-Arrière; and by the German Rückschlag, or Rückschritt. When the
child resembles either grandparent more closely than its immediate parents, our attention
is not much arrested, though in truth the fact is highly remarkable; but when the child
resembles some remote ancestor or some distant member in a collateral line,—and in the
last case we must attribute this to the descent of all the members from a common
progenitor,—we feel a just degree of astonishment. When one parent alone displays some
newly-acquired and generally inheritable character, and the offspring do not inherit it, the
cause may lie in the other parent having the power of prepotent transmission. But when
both parents are similarly characterised, and the child does not, whatever the cause may
be, inherit the character in question, but resembles its grandparents, we have one of the
simplest cases of reversion. We continually see another and even more simple case of
atavism, though not generally included under this head, namely, when the son more
closely resembles his maternal than his paternal grand-sire in some male attribute, as in
any peculiarity in the beard of man, the horns of the bull, the hackles or comb of the
cock, or, as in certain diseases necessarily confined to the male sex; for as the mother
cannot possess or exhibit such male attributes, the child must inherit them, through her
blood, from his maternal grandsire.
The cases of reversion may be divided into two main classes which, however, in some
instances, blend into one another; namely, first, those occurring in a variety or race which
has not been crossed, but has lost by variation some character that it formerly possessed,
and which afterwards reappears. The second class includes all cases in which an
individual with some distinguishable character, a race, or species, has at some former
period been crossed, and a character derived from this cross, after having disappeared
during one or several generations, suddenly reappears. A third class, differing only in the
manner of reproduction, might be formed to include all cases of reversion effected by
means of buds, and therefore independent of true or seminal generation. Perhaps even a
fourth class might be instituted, to include reversions by segments in the same individual
flower or fruit, and in different parts of the body in the same individual animal as it grows
old. But the two first main classes will be sufficient for our purpose.
 
 
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