On germinal selection as a source of definite variation / by August Weismann ; translated from the German by Thomas J. McCormack.

  • Weismann, August, 1834-1914.
Date:
1902
Catalogue details

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

Credit: On germinal selection as a source of definite variation / by August Weismann ; translated from the German by Thomas J. McCormack. Source: Wellcome Collection.

    20/104 (page 14)
    14 GERMINAL SELECTION. esses that do and can take place at the same time in the same species. Yet all this is necessary if we wish to follow out the precise details of a given case. But perhaps the most discouraging circumstance of all is, that in scarcely a single actual instance in nature can we assert whether an observed variation is useful or not—a drawback that I distinctly pointed out some time ago.^ Nor is there much hope of better¬ ment in this respect, for think how impossible it would be for us to observe all the individuals of a species in all their acts of life, be their habitat ever so limited— and to observe all this with a precision enabling us to say that this or that variation possessed selective value, that is, was a decisive factor in determining the existence of the species. In many cases we can reach at least a probable in¬ ference, and say, for example, that the great fecundity of the frog is a property having selective value, basing our inference on the observation that in spite of this fertility the frogs of a given district do not increase. But even such inferences offer only a modicum of certainty. For who can say precisely how large this number is? Or whether it is on the increase or on the decrease? And besides, the exact degree of the fecundity of these animals is far L'om being known. Rigorously viewed, vve can only say that great fe¬ cundity must be advantageous to a much-persecuted animal. And thus it is everywhere. Even in the most in¬ dubitable cases of adaptation, as, for instance, in that of the striking protective coloring of many butterflies, Die Allmacht der Natursüchtung. A Reply to Herbert Spencer. Jena, 1893, p. 27 et seq. [Also in the Contemporary Review for September, 1893.]