Hence in
the act of fertilization two germ-plasms of slightly different
structure and tendency are mingled. The mingling of the two produces
a germ-plasm and individual differing from both of the parents.
Thus, according to Weismann's earlier view, the origin of variation
was to be sought in sexual reproduction through the mingling of
slightly different germ-plasms.
But how did these two germ-plasms come to be different? How was the
variation started? To explain this Weismann went back to the
unicellular protozoa. These animals are undoubtedly influenced by
environment and vary under its stimuli. Here the variations were
stamped upon the germ-plasm, and the commingling of these variously
stamped germ-plasms has resulted in all the variations of higher
animals.
Of late Weismann has modified and greatly improved this portion of
his theory. He now accepts the view that external influences may act
upon the germ-plasm not only in protozoa but also in all higher
animals. Variation is thus due to the action or stimulus of
external influences, supplemented by sexual reproduction.
But the very constitution of the germ-plasm and its relation to the
body absolutely forbids the transmission of acquired somatic
characteristics and of the special effects of use and disuse.
Muscular activity promotes general health, and might thus conduce to
better-nourished germ-cells and to more vigorous and therefore
athletic descendants.
Pages:
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375