In what does the interest taken by a bird--let us say by one of these guillemots--in a chick which is not its own originate? Does not the sight of it arouse, by association of ideas, all those feelings which, but shortly before, its own chick was daily arousing? And if this be so, does it not in a manner mistake it for its own? It would be interesting, were something to happen to the parents of this little chick, to see if it would be fed and taken care of by any of the other birds on the ledge. If it were to be, I should be inclined to think this the reason of it. That one bird (or pair of birds) should foster the young of another, knowing all the while that it was another's, and not its own, seems to me very unlikely. There must be some confusion of thought. By association of ideas the stranger chick would excite in the stranger bird the feelings proper to rearing, whilst at the same time supplying in itself the proper object for their translation into act. When once this point had been reached, the foster-parent, if it did not look upon the chick as its own, would have--always supposing it to be one of these guillemots here--to retain a clear recollection of the chick that it had reared, all the while that it was rearing the foundling, to keep the two distinct, and remember not only that it had finished with its own chick, and seen it leave or gone off with it from the ledge, but also that it had not had another one since then. But though I believe that mental association may call up a very clear image of some past event in a bird's mind, I cannot credit it with such retentiveness and perspicuity of memory as this. Moreover, what idea of ownership in a chick can a bird have, other than those feelings which compel it to rear it? When once they are roused, the chick before it is its own.
But has not this a bearing upon the nature and origin of sympathy? When we sympathise with others we, by a quick mental process, put ourselves in their place, and feel to a lesser degree in ourselves what we suppose them to be feeling. In a certain degree, therefore, we are them, but our reason assures us that this is not really the case. We can distinguish; but can animals, or can they other than partially? Anthropologists have much to say--sometimes, perhaps, almost too much--on the extent to which savages mistake their subjective impressions for objective reality; but what applies to the savage should apply with much greater force to the animal. When a herd of fierce animals--as, say, of peccaries--are filled with sudden rage at the sight of a companion struck down by some beast of prey--bear, jaguar, or puma--and attack the assailant, is each member of it distinctly conscious that he is acting in defence of another, or does he not, rather, imagine that he is repelling an attack made upon himself? I believe myself that this last, or something very like it, is really the case, and that sympathy, if traced far enough back along the line of our descent, would lead us to a time when it made no conscious distinction between itself and its object; thus rooting our best feelings in the purest selfishness.