Romanes, one of Weismann’s ablest critics, compares Weismann’s theory with Darwin’s, and while he refuses to defend Pangenesis against Weismann’s charge that it is a wholly unsupported speculation, he replies by contending that the germ-plasm theory lives in precisely the same kind of a glass house.
However that may be, it is quite clear that the germ-plasm theory completely shuts out the Lamarckian factor of evolution in all cases where propagation is sexual.
“But,” say the Neo-Lamarckians, “Darwinism in itself, merely assumes variations without attempting to explain their origin. Natural selection only explains the survival of the fittest; it tells us nothing of what Prof. Cope calls the ‘Origin of the Fittest.’ There must be variation before selection, whence then, comes this variation?” To this question Weismann has a ready reply. “Variation is due to the blending of two wholly different kinds of germ-plasm at conception, producing at birth a result that is not, and cannot be, wholly like the contributor of either.”
And now, at last, the great German is in a corner. If all variations are due to congenital characters only, and these, of course, are only possible because of the combinations secured by sexual reproduction, how do variations arise among non-sexual organisms where such combinations cannot exist?
This is indeed, a poser. But any rejoicing by Weismann’s opponents is quite premature. The sagacity which set those opponents by the ears is still available. There is no attempt to untie that knot; Weismann cuts it with a knife. He empties his antagonist’s sails by a smiling and gracious surrender. Below the sexually reproducing animals, he concedes the operation of the Lamarckian factor. In that unicellular world it is not a special cell that is passed on but the individual itself is continued, and of course any character acquired by the individual will be preserved along with the individual.
Thus then the region of controversy is limited to sexually reproducing organisms and we come to the field where the fiercest fight was made. Do these organisms transmit by heredity those characters or peculiarities acquired by the individual during its own life-time? To this question the Neo-Lamarckians gave a positive affirmative, which Weismann met with an unwavering denial.