The explanation of natural selection would be quite different. The
Darwinian would say that all the young giraffes of any one generation
would vary with respect to the length of the neck. Those with longer necks
would have a slight advantage over their fellows in the extended sphere of
their grazing territory. Being better nourished than the others, they
would be stronger and so they would be more able to escape from their
flesh-eating foes, like the lion. For the reason that their variation
would be congenital and therefore already transmissible, their offspring
would vary about the advanced condition, and further selection of the
longer necked individuals would lead to the modern result.
The Lamarckian explanation encounters one grave difficulty which is not
met by the second one, in so far as it demands some method by which a
bodily change may be introduced into the stream of inheritance. So far,
this difficulty has not been overcome, and the present verdict of science
is that the transmission of characters acquired as the result of other
than congenital factors is not proved. It would be unscientific to say
that it cannot be proved in the future, but there are good _a priori_
grounds for disbelief in the principle, while furthermore the results of
experiments that have been undertaken to test its truth have been entirely
negative.
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