Fast eBooks

It is an error to assume that
what seem to us identical conditions are really identical to such small
and delicate organisms as these land molluscs, of whose needs and
difficulties at each successive stage of their existence, from the
freshly-laid egg up to the adult animal, we are so profoundly ignorant.
The exact proportions of the various species of plants, the numbers of
each kind of insect or of bird, the peculiarities of more or less
exposure to sunshine or to wind at certain critical epochs, and other
slight differences which to us are absolutely immaterial and
unrecognisable, may be of the highest significance to these humble
creatures, and be quite sufficient to require some slight adjustments of
size, form, or colour, which natural selection will bring about. All we
know of the facts of variation leads us to believe that, without this
action of natural selection, there would be produced over the whole area
a series of inconstant varieties mingled together, not a distinct
segregation of forms each confined to its own limited area.


Pages:
252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276