First, account must be taken of the fact that the various groups or agents of production are not entirely complementary, as has been assumed up to this point. Their outstanding relation--that of cooperation in the production of a joint product--has already been studied. But there is also a measure of genuine competition between them for the field of employment. An unusually clear and detailed example of the nature of this competition is to be found in the report of the commission on "The Decline of the Agricultural Population in Great Britain." To quote "Many expedients, other than actually stopping the plow, were adopted to reduce the labor bill. But while manual labor has no doubt been economized to some extent by curtailing some of the operations which require it, the main cause of reduction is undoubtedly the extended use of labor saving machinery. This is referred to by the large majority of correspondents in all parts of the country. With the exception of the self-binding harvester, which was introduced into this country in the eighties, few machines for the performance of a specific manual operation have perhaps been invented since 1891 (unless milking machines, shearing machines, and perhaps potato diggers come within that category), but whereas twenty years ago labor saving machinery was fully employed by comparatively few, it has now become almost universal on all holdings of sufficient size to make its use practicable. The substitution of mechanical for horse or hand power, for mixed machinery, e.g., threshing machines, chaff cutters, pumps, etc., has taken place largely, although it has made comparatively little progress for tractive purposes. It may indeed, be questioned if steam is so largely employed in the cultivation of land as it was twenty years ago. But the displacement of manual labor arising from the greatly extended use of drills, horse hoes, mowers, binders, manure distributors and the like must have been in the aggregate very great and probably to this more than to any other single cause the reduced demand for farm laborers may be attributed."[24] As Professor Marshall has remarked of such cases of competition for employment between labor and capital as this, the competition is in reality between one kind of labor aided by much waiting, and another kind of labor aided by little waiting. Nevertheless, the fact of competition between the various groups or agents is a fact of no mean importance in distribution. As has already been suggested, the efficiency of the wage earners plays a part in determining their field of employment in this competition for employment.