There  is  another  objection  of  nearly  the  same  char-
acter, which  must  have  struck  every  thinker  with  more
or  less  force.  How  are  the  various  organs  of  a  highly
complicated  organism,  or  the  various  structures  w^hicli
enter  into  the  formation  of  a  complicated  organ,  kept  in
harmonious  adjustment  to  each  other  by  the  selection  of
variations  which  are,  in  Darwin's  sense,  fortuitous?  It
is  plain  that,  as  soon  as  one  part  has  varied  in  any  direc-
tion, the  harmonious  adjustment  of  related  parts  w^ill  be
disturbed,  and  that  tliey  too  must  vary  correspondingly
in  order  to  restore  the  proper  tone  to  the  whole,  and  it
is  equally  clear  that  even  a  slight  change  in  a  compli-


282  Heredity.
cated  organ  will  thus,  if  the  yarious  modifications  are
really  fortuitous,  require  a  very  great  number  of  genera-
tions to  supply  the  necessary  variations.
There  does  not  seem  to  be  any  logical  ground  for
doubting  that  any  of  the  adaptations  of  nature  might
have  been  produced  by  the  natural  selection,  from  an  in-
definite number  of  fortuitous  variations,  of  those  which
happened  to  be  favorable;  but  in  the  case  of  any  com-
plex adaptation,  an  indefinite  and  almost  infinite  period
of  time  would  be  required.
