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We have already seen that use-inheritance is unnecessary, since natural selection will be far more effective in bringing about advantageous modifications; and if it can be shown that use-inheritance would often be an evil, it then becomes probable that on the whole natural selection would more strongly discourage and eliminate it as a hostile factor than it might occasionally favour such a tendency as a totally unnecessary aid.
Some of the bones of the rudimentary hind legs of the whale are still in existence after disuse for an enormous period. Evidently use-inheritance could not equally modify the turtle and its shell, or the brain and its skull; and in minor matters there would be the same incongruity of effect. Thus, if the molar teeth lengthened from extra use the incisors could not meet.
Even the alleged instances of use-inheritance culled by such great and judicious selectors as Darwin and Spencer break down upon examination; for they can be better explained without use-inheritance than with it. On the other hand, the adverse facts and considerations are almost strong enough to prove the actual non-existence of such a law or tendency.
If natural selection had on the whole favoured this officious ally and frequent enemy, surely we should find better evidence of its existence. Without laying undue stress upon the evil effects of use-inheritance, a careful examination of them in detail may at least serve to counter-balance the optimistic a priori arguments for belief in that plausible but unproven factor of evolution.
Nestlings which acquire the song of a distinct species, "teach and transmit their new song to their offspring." If use-inheritance has not fixed the song of birds, why should we suppose that in a single generation it has transmitted a newly-taught method of walking or trotting?
I therefore see no necessity whatever for calling in the aid of use-inheritance as Darwin does, to account for enlarged udders, or diminished lungs, or the thick arms and thin legs of canoe Indians, or the enlarged chests of mountaineers, or the diminished eyes of moles, or the lost feet of certain beetles, or the reduced wings of logger-headed ducks, or the prehensile tails of monkeys, or the displaced eyes of soles, or the altered number of teeth in plaice, or the increased fertility of domesticated animals, or the shortened legs and snouts of pigs, or the shortened intestines of tame rabbits, or the lengthened intestines of domestic cats, &c.
The fact that uneducated persons do not enjoy the higher tastes, and the rapidity with which such tastes are acquired or professed, ought to be sufficient proof that modern culture is brought about by far swifter and more potent influences than use-inheritance.
Where intelligence is not highly valued and carefully promoted by selection, the intelligence derivable from association with man does not appear to be inherited. Lap-dogs, for instance, are often remarkably stupid. Darwin also instances the inheritance of dexterity in seal-catching as a case of use-inheritance. But this is amply explained by the ordinary law of heredity.
For satisfactory proof of the prevalence of a law of use-inheritance we require normal instances where selection is clearly inadequate to produce the change, or where it is scarcely allowed time or opportunity to act, as in the immediate offspring of the modified individual. Of the first kind of cases there seems to be a plentiful lack.
Under these circumstances how can we be sure of the actual efficacy of use-inheritance? Surely selection is as fully competent to effect slight changes in the direction of use-inheritance as it undoubtedly is to effect great changes in direct opposition to that alleged factor of evolution. The shortening of the sternum in pigeons is attributed to disuse of the flight muscles attached to it.
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