Page:Popular Science Monthly Volume 26.djvu/607

Rh from time to time fresh food to her young, and remembers very exactly the entrance to her cell, although she has covered it with sand, so as not to be distinguishable from the surrounding surface. Yet M. Fabre found that if he brushed away the earth and the underground passage leading to the nursery, thus exposing the contained larva, the parent insect "was quite at a loss, and did not even recognize her own offspring. It seemed as if she knew the doors, nursery, and the passage, but not her child."

Lastly, instinct is always similarly manifested under similar circumstances by all the individuals of the same species. And, it may be added, these circumstances are always such as have been of frequent occurrence in the life-history of the species.

Now, in all these respects instinct differs conspicuously from every other faculty of mind, and especially from reason. Therefore, to gather up all these differentiæ into one definition, we may say that instinct is the name given to those faculties of mind which are concerned in consciously adaptive action, prior to individual experience, without necessary knowledge of the relation between means employed and ends attained; but similarly performed under similar and frequently recurring circumstances by all the individuals of the same species.

Such being my definition of instinct, I shall now pass on to consider Mr. Darwin's theory of the origin and development of instincts.

Now, to begin with, Mr. Darwin's theory does not, as many suppose that it does, ascribe the origin and development of all instincts to natural selection. This theory does, indeed, suppose that natural selection is an important factor in the process; but it neither supposes that it is the only factor, nor even that in the case of numberless instincts it has had anything at all to do with their formation. Take, for example, the instinct of wildness, or of hereditary fear as directed toward any particular enemy—say man. It has been the experience of travelers who have first visited oceanic islands without human inhabitants, and previously unvisited by man, that the animals are destitute of any fear of man. Under such circumstances the birds have been known to alight on the heads and shoulders of the new-comers, and wolves to come and eat meat held in one hand while a knife was held ready to slay them with the other. But this primitive fearlessness of man gradually passes into an hereditary instinct of wildness, as the special experiences of man's proclivities accumulate; and, as this instinct is of too rapid a growth to admit of our attributing it to natural selection (not one per cent of the animals having been destroyed before the instinct is developed), we can only attribute its growth to the effects of inherited observation. In other words, just as, in the lifetime of the individual, adjustive actions which were originally intelligent may by frequent repetition become automatic, so in the lifetime of the species, actions originally intelligent may, by frequent repetition and heredity, so write their effects on the nervous system