All this may seem to undervalue or perhaps to overlook the physical facts of industry and the physical nature of commodities. There is, of course, no call to understate the importance of material goods or of manual labor. The goods about which this inquiry turns are the products of trained labor working on the available materials; but the labor has to be trained, in the large sense, in order to be labor, and the materials have to be available in order to be materials of industry. And both the trained efficiency of the labor and the availability of the material objects engaged are a function of the "state of the industrial arts." Yet the state of the industrial arts is dependent on the traits of human nature, physical, intellectual, and spiritual, and on the character of the material environment. It is out of these elements that the human technology is made up; and this technology is efficient only as it meets with the suitable material conditions and is worked out, practically, in the material forces required. The brute forces of the human animal are an indispensable factor in industry, as are likewise the physical characteristics of the material objects with which industry deals. And it seems bootless to ask how much of the products of industry or of its productivity is to be imputed to these brute forces, human and non-human, as contrasted with the specifically human factors that make technological efficiency. Nor is it necessary to go into questions of that import here, since the inquiry here turns on the productive relation of capital to industry; that is to say, the relation of the material equipment and its ownership to men's dealings with the physical environment in which the race is placed. The question of capital goods (including that of their ownership and therefore including the question of investment) is a question of how mankind as a species of intelligent animals deals with the brute forces at its disposal. It is a question of how the human agent deals with his means of life, not of how the forces of the environment deal with man. Questions of the latter class belong under the head of Ecology, a branch of the biological sciences dealing with the adaptive variability of plants and animals. Economic inquiry would belong under that category if the human response to the forces of the environment were instinctive and variational only, including nothing in the way of a technology. But in that case there would be no question of capital goods, or of capital, or of labor. Such questions do not arise in relation to the non-human animals.