During life’s existence on earth--a period to be reckoned in hundreds and probably in thousands of millions of years--there has been an increase in various of its attributes. But just as in the inorganic world electrons and atoms still exist as such side by side with molecules, so also the earlier types of living matter continue to exist side by side with the later. The increase is not therefore seen uniformly in all forms at once, but is most easily observed by studying the _maximum_ level attained. Size, for instance, is one of these attributes; and whereas to-day all variations are to be found between ultra-microscopic disease-germs and vast organisms like whales and elephants, there has been a gradual steadying increase (tending to a limit) in the size of the _largest_ organisms existing at any one period. If we confine ourselves for the moment to the material side, we find that the directional change in organic evolution can be reduced to this--to an increase of the control exercised by living matter over the environment, and of its independence of the environment--two reciprocal aspects of a single process. When we look more closely into the means by which this has been achieved, we shall see an increase of the maximum not only in size, but in complexity, in length of life, in efficiency of particular organs, in co-ordination of parts and general harmony, in improvement of sense-organs, and, continuing even after other tendencies have reached their limits, in brain-size and consequently in complexity of mode of reaction and behaviour. If we turn to the psychological side, we find that there has been an increase in the intensity of mental process. This is apparent in all aspects of mind, on that of emotion equally with that of knowledge, of volition equally with that of emotion. To be an amoeba or a worm is to live a life almost without windows. Perfection of sense-organs makes it possible for life to be aware of the different types of outer events, whilst memory and, later, associative memory give the possibility of understanding their history. In higher forms volition can be maintained for longer and longer intervals, can attain greater intensity, and can fix itself upon ever more and more distant objects. With depth of feeling comes also differentiation, so that finally we find in ourselves the possibility of organizing various blends of the simple emotions into the compound emotional forms such as reverence and admiration, called _sentiments_ by McDougall. Biologically speaking, therefore, the direction observable in mental evolution is again towards increased control and increased independence; by mental and cerebral improvement there is introduced a greater accuracy and a greater range of control, as well as better adjustment between organisms and environment, than would be otherwise possible to the same bodily organs.