Heredity / by J.A.S. Watson.

  • James Anderson Scott Watson
Date:
[1912]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Heredity / by J.A.S. Watson. Source: Wellcome Collection.

    40/104 page 38
    88 HEREDITY ance of modifications are doubtless mere coincidences. It is a rather unconvincing^ explanation of an individual case, perhaps, to call it a coincidence; but such coincidences must occasionally occur, and the probability is that a large proportion of them are recorded. It must be said, then, that evidence of the inheritance of mutilations is extremely scanty and unsatisfactory. The extreme rarity of supposed cases, in the first place, must make one somewhat sceptical. If modification inheritance were possible we should expect it to occur in a fair percentage of cases. Of alleged cases, many will not bear close inspection, and in most there is some other explanation at least possible. It seems fair to conclude that such few cases as are not open to objec¬ tion may probably be coincidences. A large group of modifications may be classed as the effects of use and disuse of organs, and it is perhaps with regard to the possibility of the inheritance of such effects that the greater part of the whole controversy has arisen. Many biologists are of the opinion that mutilations, having often but a very slight effect on the general system, wiU not as a rule be inherited. But the effects of use and disuse, they claim, burrow deep into the whole organisation, and are thus much more likely to affect the germ cells. In the process of evolution, many things have occurred which are easy of explanation if we assume that the effects of use and disuse are inherited, and some of them are hard to explain on any other hypothesis. The hind limbs of the whale long ago ceased to be used, and they have now all but disappeared. The wings of the ostrich have ceased to be used for flight, and they have become greatly reduced. The remote ancestor of our present-day horse began to walk on the tips of his toes, with the result that the middle toe of the five began to bear most of the weight. Since then the middle toe has become very much larger, and the others have disappeared except for two small rudi¬ ments.
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