IMPORTANCE OF THE CONSIDERATION OF AFFINITIES
Among living bodies the name affinity has been given
to features of analogy or resemblance between two objects, that are compared
in their totality, but with special stress on the most essential parts. The
closer and more extensive the resemblance, the greater the affinities. They
indicate a sort of kinship between the living bodies which exhibit them;
and oblige us in our classification to place these bodies in a proximity
proportional to their affinities.
How great has been the progress of natural science
since serious attention began to be given to affinities, and especially since
their true underlying principles have been determined!
Before this change, our botanical classifications
were entirely at the mercy of arbitrary opinion, and of artificial systems
of any author. In the animal kingdom, the invertebrate animals comprising
the larger part of all known animals were classified into the most heterogeneous
groups, some under the name of insects, some under the name of worms; where
the animals included are from the point of view of affinity widely different
from one another.
We must then be guided everywhere by natural
affinities in composing the groups which result by dividing each kingdom
into classes, each class into orders, each order into sections or families,
each family into genera, and each genus into different species if there is
occasion for it.
There is thorough justification for the belief that
the complete series of beings making up a kingdom represents the actual order
of nature, when it is classified with direct reference to affinities; but,
as I have already pointed out, the different kinds of divisions which have
to be set up in that series to help us distinguish objects with greater ease
do not belong to nature at all. They are truly artificial although they exhibit
natural portions of the actual order instituted by nature.