Occasionally we can find
such cases, as in that of Branchipus stagnalis, quoted by Mr.
Wallace, or in that of the New Zealand Kea whose skin, I was assured
by the late Sir Julius von Haast, has already been modified as a
consequence of its change of food. Here we can show that in even a
few generations structure is modified under changed conditions of
existence, but as we believe these cases to occur comparatively
rarely, so it is still more rarely that they occur when and where we
can watch them. Nature is eminently conservative, and fixity of
type, even under considerable change of conditions, is surely more
important for the well-being of any species than an over-ready power
of adaptation to, it may be, passing changes. There could be no
steady progress if each generation were not mainly bound by the
traditions of those that have gone before it. It is evolution and
not incessant revolution that both parties are upholding; and this
being so, rapid visible modification must be the exception, not the
rule.
Pages:
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440