In
cultivation this is the process of variety-testing. In nature it is the
survival of the fittest species, or, as Morgan designates it, the
survival of species in the struggle for existence. The species are not
changed by this struggle, they are only weighed against each other, the
weak being thrown aside.
Within the chosen elementary species there is also a struggle. It is
obvious, that the fluctuating variability adapts some to the given
circumstances, while it lessens the chances of others. A choice results,
and this choice is what is often exclusively called selection, either
natural or artificial. In cultivation it produces the improved and the
local races; in nature little is known about improvement in this way,
but [19] local adaptations with slight changes of the average character
in separate localities, seem to be of quite normal occurrence.
A new method of individual selection has been used in recent years in
America, especially by W.M. Hays. It consists in judging the hereditary
worth of a plant by the average condition of its offspring, instead of
by its own visible characters. If this determination of the "centgener
power," as Hays calls it, should prove to be the true principle of
selection, then indeed the analogy between natural and artificial
selection would lose a large part of its importance.
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