But if these two forms freely intercross with each other and produce hybrids which are also quite fertile inter se, then the formation of the two distinct races or species will be retarded or perhaps entirely prevented; for the offspring of the crossed unions will be more vigorous owing to the cross, although less adapted to their conditions of life than either of the pure breeds. (211/2. After "pure breeds," add "because less specialised." A.R.W. (1899).)英文原著 · 《More Letters of Charles Darwin Volume I》
Only let the progress not be misunderstood. The logical Idea does not thereby
come into possession of a content originally foreign to it: but by its own native action is specialised
and developed to Nature and Mind.英文原著 · 《Shorter Logic》