lanation of this fact would be that the earliest forms in
the ancestry of the giraffe as such stretched their necks as they fed, and
that this peculiar function with its correlated structural modification
became habitual. The slight increase brought about by any single
individual would be inherited and transmitted to the giraffes of the next
generation; in other words, an individually acquired character would be
inherited. The young giraffes of this next generation would then begin,
not where their parents did, but from an advanced condition. Thus, by
continued stretching of the neck and by continued transmission of the
elongated condition, the great length of this part of the body in the
modern giraffe would be attained.

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. Rats and mice have had their tails cut off to see if this
mutilation would have its effect upon their young, and though this has
been done for more than one hundred successive generations the length of
the tail has not been altered. Quite unconscious of the scientific
problem, many human races have performed precisely similar experiments
through centuries of time. In so