We have in a previous chapter spoken at sufficient length of the incalculable æsthetic importance of rhythm as a means of producing emotional community between different individuals. In this connection we have still to point out that a fixed time-division must in the same way facilitate common activity. From the historical point of view this practical aspect is undoubtedly the more important. However fundamental and primordial the æsthetic function of the perception of rhythm may seem for the theorist, it is most probable that the development of this faculty has been chiefly furthered by its utilitarian advantages. There is no doubt that even the most primitive man may feel the want of associating his fellow-men in his emotions, and that for this purpose he may be able to give the expression of them a fixed rhythmical form. But the power of perceiving this time-division as a rhythm, and of obeying it closely in song and dance, would, as Dr. Wallaschek has shown, certainly not have attained so high a degree of development if this power had not, by facilitating common activity, been of such immense advantage for the maintenance of species.[409] It goes without saying that any work which necessitates the co-operation of several workers must be executed with greater efficiency the more closely the individuals follow to a common rhythm. There is no doubt, therefore, that, as Spencer remarks, the incompetence of the Arab and Nubian boatmen on the Nile is chiefly a result of their inability to act together. As an Arab dragoman is reported to have said, a few Europeans would, by virtue only of their superior powers of co-operation, do in a few minutes what now occupies hundreds of men.[410] Such an incapacity for concerted action is, however, quite exceptional among the lower tribes of men. Some tribes, as _e.g._ the farmer Negroes in West Africa and the Malay and Polynesian boatmen, are even famous for the wonderful regularity of their work.[411] This regularity, on the other hand, has been explained by all travellers as a result of the rhythmical songs by which their work is accompanied.