Page:The Harveian oration (electronic resource) - Royal College of Physicians, 1881 (IA b20411911).pdf/31

 this proved, it would go no further than to serve as an illustration of the survival of the fittest within the limits of the species. No one has ever ventured to assert that the fruit of these mingled races could not themselves intermarry and produce fruitful offspring. The unity of the species remains unquestioned.

The subject of survivals has again been brought into prominence, in connection with Professor Darwin's theory of natural selection, by a certain section of philosophers, who profess to range themselves under his banner. The wild speculations which now pass current under the name of Darwinianism, start with the assumption that if there be apparently no limit to the origin of varieties within the bounds of species, there should be no difficulty in the transition from one species to another. I do not propose to argue the grounds on which this assumption is supposed to rest. I would only ask whether Nature has been questioned in the sense which Bacon and Harvey alike propose, and what answer she has given. I am not exaggerating the opinions held by these advanced thinkers, in saying that one of their dogmatic beliefs is that no single species has been throughout its history quite unconnected with other genera or species than its own, or was evolved at any one particular time or place in the world's history. It has been pointed out, without altering the current