resemble one another closely. While they vary somewhat in form, the range
in this quality is not so noticeable as in the matter of color; some of
them will be gray, some maltese, while others will be yellowish or black,
and they will differ in the striped or spotted character of their
coloration. We readily classify them all as "cats" in spite of their
differences, because they are alike in so many ways that we have learned
to associate as the distinguishing characteristics of these animals, and
to label--"cat." The animals which we might see in a walk of several
blocks may reasonably be regarded as offspring of the same pair of
ancestors of a few years back, even though they are dissimilar. We all
know that the kittens of one and the same litter vary: no two of them are
ever exactly alike in color or disposition or voice or size, nor is any
one identical with either of its parents, although it may be necessary to
employ exact means of measuring them in order to demonstrate their
variation. The fact of difference, then, is surely not inconsistent with
even the closest ties of blood, and we do not need to go beyond the scope
of daily observation to find that this is true in nature wherever we look.

Should we extend our observations so as to include the cats of Boston and
Philadelphia and San Francisco, the animals would probably vary over a
wider range, but they would be so similar to New York cats in their
make-up that we would have no difficulty in regarding them and all the
others of the United States as the descendants of a single pairs of
ancestors, perhaps brought over in the "Mayflower." But why does this view
seem justified? Because experience has taught us that the living things
which resemble each other most closely are those which are most intimately
bound by ties of blood and common heritage. It is "natural" for relatives
to resemble one another more than persons not related, and for brothers and
sisters to be more alike than cousins. Science does not refer to something
outside everyday observation when it states that _the possession by two