The somatoplasm can only in the most general way affect the
self-perpetuating, close corporation of the germ-plasm.[A]
[Footnote A: Weismann, Essays, p. 286.]
There is thus, according to Weismann, nothing to direct variation to
certain organs, or to guide and combine the variations of these
organs along certain lines, except natural selection. To a certain
extent variation may be limited by the very structure of the animal.
But within these limits there are wide ranges where one variation is
apparently just as likely to occur as another.
Within these wide limits variation appears to be fortuitous. Natural
selection must wait until the individuals appear in which these
variations occur already correlated, and then seize upon these
individuals. It is apparently the only guiding, directing force.
Linear variation, that is, a variation advancing continuously along
one or very few straight lines, would appear to be impossible.
In Naegeli's theory initial tendency is overwhelmingly dominant; in
Weismann's, natural selection is almighty.
Weismann's followers have received the name of Neo-Darwinians. The
so-called Neo-Lamarckian school believes in the transmissibility of
acquired characteristics, and of at least particular effects of use
and disuse. The one theory is neither more nor less Darwinian than
the other.
Pages:
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377