the mass of diversified details out of which the Origin of Species and the other derivative coördinate works grew, it is hard to see in what way his course could have been improved. The ill-health which seized him so soon was almost a blessing in disguise, since it isolated him from the distractions of modern London, made him value his life and his time, and possibly, by the economy of his strength which it necessitated, aided as much as it hindered him.
One need not follow him through the composition of his books, or even through the elaboration of the theory of natural selection, during the many years that it was growing in his laboratory of notes. For him the formulating of that theory was inevitable: it seems, as one observes him, natural enough to have been foretold of him; but it followed, not from his position, which another man might have occupied, but from his genius. The qualities of mind which it required were not many, and one understands readily why it is so commonly said that all is explained by his power of observation and its vast range; but it did require one high faculty of the mind, and a rare one, which Darwin had preëminently among
