Can this be regarded as the
inheritance of a long continued process of use and disuse? Such a view
is often taken, but the Lamarckian doctrine seems to us just as mystical
here as anywhere else, and no more necessary. Progressive changes can be
satisfactorily accounted for by natural selection; retrogressive changes
are susceptible of explanation along similar lines. When an organ is no
longer necessary, as the hind legs of a whale, for instance, natural
selection no longer keeps it at the point of perfection. Variation,
however, continues to occur in it. Since the organ is now useless,
natural selection will no longer restrain variation in such an organ,
and degeneracy will naturally follow, for of all the variations that
occur in the organ, those tending to loss are more numerous than those
tending to addition. If the embryonic development of a whale's hind leg
be compared to some complicated mechanical process, such as the
manufacture of a typewriter, it will be easier to realize that a trivial
variation which affected one of the first stages of the process would
alter all succeeding stages and ruin the final perfection of the
machine. It appears, then, that progressive degeneration of an organ can
be adequately explained by variation with the removal of natural
selection, and that it is not necessary or desirable to appeal to any
Lamarckian factor of an unexplainable and undemonstrable nature.
Pages:
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84