Page - 259 - in The Origin of Species

THEORY OF NATURAL SELIXTION 259 changed as abruptly as have occasionally domestic races, and for entirely disbelieving that they have changed in the won- derful manner indicated by Mr. Mivart, are as follows. Ac- cording to our experience, abrupt and strongly marked vari- ations occur in our domesticated productions, singly and at rather long intervals of time. If such occurred under na- ture, they would be liable, as formerly explained, to be lost by accidental causes of destruction and by subsequent inter- crossing; and so it is known to be under domestication, un- less abrupt variations of this kind are specially preserved and separated by the care of man. Hence in order that a new species should suddenly appear in the manner supposed by Mr. Mivart, it is almost necessary to believe, in opposition to all analogy, that several wonderfully changed individuals appeared simultaneously within the same district. This dif- ficulty, as in the case of unconscious selection by man, is avoided on the theory of gradual evolution, through the pres- ervation of a large number of individuals, which varied more or less in any favourable direction, and of the destruction of a large number which varied in an opposite manner. That many species have been evolved in an extremely gradual manner, there can hardly be a doubt. The species and even the genera of many large natural families are so closely allied together, that it is difficult to distinguish not a few of them. On every continent in proceeding from north to south, from lowland to upland, &c., we meet with a host of closely related or representative species ; as we likewise do on certain distinct continents, which we have reason to believe were formerly connected. But in making these and the following remarks, I am compelled to allude to subjects hereafter to be discussed. Look at the many outlying islands round a continent, and see how many of their inhabitants can be raised only to the rank of doubtful species. So it is if we look to past times, and compare the species which have just passed away with those still living within the same areas; or if we compare the fossil species embedded in the sub-stages of the same geological formation. It is indeed manifest that multitudes of species are related in the closest manner to other species that still exist, or have lately existed ; and it will hardly be maintained that such species have been developed