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The Variation of Animals and Plants

Chapter XII: Inheritance
WONDERFUL NATURE OF INHERITANCE — PEDIGREES OF OUR DOMESTICATED ANIMALS
— INHERITANCE NOT DUE TO CHANCE — TRIFLING CHARACTERS INHERITED — DISEASES
INHERITED — PECULIARITIES IN THE EYE INHERITED — DISEASES IN THE HORSE —
LONGEVITY AND VIGOUR — ASYMMETRICAL DEVIATIONS OF STRUCTURE —
POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER AMPUTATION —
CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS —
WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR
OF FRUIT AND FLOWERS — COLOUR OF HORSES — NON-INHERITANCE IN CERTAIN CASES
— INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS OF
LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION — CONCLUSION.
The subject of inheritance is an immense one, and has been treated by many authors. One
work alone, 'De l'Hérédité Naturelle' by Dr. Prosper Lucas, runs to the length of 1562
pages. We must confine ourselves to certain points which have an important bearing on
the general subject of variation, both with domestic and natural productions. It is obvious
that a variation which is not inherited throws no light on the derivation of species, nor is
of any service to man, except in the case of perennial plants, which can be propagated by
buds.
If animals and plants had never been domesticated, and wild ones alone had been
observed, we should probably never have heard the saying, that "like begets like." The
proposition would have been as self-evident as that all the buds on the same tree are
alike, though neither proposition is strictly true. For, as has often been remarked,
probably no two individuals are identically the same. All wild animals recognise each
other, which shows that there is some difference between them; and when the eye is well
practised, the shepherd knows each sheep, and man can distinguish a fellow-man out of
millions on millions of other men. Some authors have gone so far as to maintain that the
production of slight differences is as much a necessary function of the powers of
generation, as the production of offspring like their parents. This view, as we shall see in
a future chapter, is not theoretically probable, though practically it holds good. The
saying that "like begets like" has, in fact, arisen from the perfect confidence felt by
breeders, that a superior or inferior animal will generally reproduce its kind; but this very
superiority or inferiority shows that the individual in question has departed slightly from
its type.
The whole subject of inheritance is wonderful. When a new character arises, whatever its
nature may be, it generally tends to be inherited, at least in a temporary and sometimes in
a most persistent manner. What can be more wonderful than that some trifling
peculiarity, not primordially attached to the species, should be transmitted through the
male or female sexual cells, which are so minute as not to be visible to the naked eye, and
afterwards through the incessant changes of a long course of development, undergone
either in the womb or in the egg, and ultimately appear in the offspring when mature, or
even when quite old, as in the case of certain diseases? Or again, what can be more
wonderful than the well-ascertained fact that the minute ovule of a good milking cow will
produce a male, from whom a cell, in union with an ovule, will produce a female, and
 
 
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