Origin of Species Variorum

natural selection having taken advantage of numerous, successive, slight modifications of simpler instincts; natural selection having by slow degrees, more and more perfectly, led the bees to sweep equal spheres at a given distance from each other in a double layer, and to build up and excavate the wax along the planes of intersection. The bees, of course, no more knowing that they swept their spheres at one particular distance from each other, than they know what are the several angles of the hexagonal prisms and of the basal rhombic plates. The motive power of the process of natural selection having been economy of wax, together with cells of due strength, and of the proper size and shape for the larvæ; that individual swarm which made the best cells, and wasted least honey in the secretion of wax, having succeeded best, and having transmitted by inheritance their newly acquired economical instincts to new swarms, which in their turn will have had the best chance of succeeding in the struggle for existence. ↑ ↑

It has been objected to the foregoing view on the origin of instinct that "the variations of structure and of instinct must have been simultaneous and accurately adjusted to each other, as a modification in the one without an immediate corresponding change in the other would have been fatal." The force of this objection seems entirely to rest on the assumption that the changes in both instinct and structure are abrupt. To take as an illustration the case of the larger titmouse (Parus major) alluded to in the last chapter: this bird often holds the seeds of the yew between its feet on a branch, and hammers away till it gets into the kernel. Now what special difficulty would there be in natural selection preserving each slight variation of beak, better and better adapted to break open seeds, until a beak was formed, as well constructed for this purpose as that