What has led to the truly wonderful result which we admire in a creature
like a dog or an otter, a horse or a hare? In general, we may say, just
two main processes--(1) testing all things, and (2) holding fast that
which is good. New departures occur and these are tested for what they
are worth. Idiosyncrasies crop up and they are sifted. New cards come
mysteriously from within into the creature's hand, and they are
played--for better or for worse. So by new variations and their sifting,
by experimenting and enregistering the results, the mind has gradually
evolved and will continue to evolve.