Fifthly, there has been an increase in the possibility of bringing past experience to bear on present problems. At the base is the power of modifying normal reactions with repetition; then come some simple degrees of memory; then associative memory, as in birds and mammals, for whom most reactions are not given in the inherited constitution, but must be learnt; then rational memory, in which the power of generalization liberates life from blind dependence upon the local and the accidental; and finally tradition, whereby the amount of experience available to the developing race is not constituted merely by the isolated and limited experiences of its members, but by their sum. More and more of the past becomes directly operative in the present; further and further into the future can the aim of the present extend. Finally we can conclude with a high degree of certainty that the psychical faculties--of knowing, feeling, and willing--have increased in intensity, and also in their relative importance for the life of the individual organism. We have condensed our summary into these six general statements; if we wish to reach a still more general form, the most general form possible, we can redistil it thus: During the course of evolution in time, there has been an increase in the control exerted by organisms over their environment, and in their independence with regard to it; there has been an increase in the harmony of the parts of organisms; and there has been an increase in the psychical powers of organisms, an increase of willing, of feeling, and of knowing. This increase has not been universal; many organisms have remained stationary or have even regressed; many have shown increase in one particular but not in others. But the _upper level_ of these properties of living matter has been continually raised, their average has continually increased. It is to this increase, continuous during evolutionary time, in the average and especially in the upper level of these properties that, I venture to think, the term biological progress can be properly applied. Used thus it is no more an a priori or an undefined concept. It is a name for a complicated set of actual phenomena, and if, with progress thus defined, we were to speak of a law of progress in evolution, we should be using the term law in a perfectly legitimate way, as denoting a generalization based on observed facts, and not as pre-supposing any vitalistic principle of perfectibility, any necessary and mysterious tendency of organisms to advance independently of circumstances.