some control over the local distribution of species is of paramount importance. Nevertheless, if all the different forms that require similar conditions of existence were intolerant of one another in a like degree, the smaller bird would have no chance in competition with the larger. This, however, is not the case. Some, as we saw, arouse little or no animosity in others, in fact the more closely related the rivals, the more responsive their pugnacious nature seems to become.
To return now to the view that the fighting is not really serious, but, on the contrary, that it is either vestigial and has no longer any part to play in furthering the life of the individual, or that it is a by-product of the seasonal sexual condition to which no meaning can be attached. First, there is the relationship with the territory, and this, it seems to me, is a fact of some importance; for if the fighting were merely an exuberant manifestation of sexual emotion, one would expect to find it occurring under all conditions, and not merely under one particular condition in the life of the bird. The hostility is too widespread, however, and too uniform in occurrence for us to suppose that it has no root in the inherited constitution of the bird; and if it served some useful purpose in the past, the instinct might still persist, so long as it were not harmful. Thus the view that the behaviour is vestigial is not perhaps unreasonable. But manifestly it makes no difference whether it be vestigial or a by-product of sexual emotion.
