The author considers that psycho-analytical theory is not only 'in accord with the facts of evolution' (he is especially struck by the plasticity of the instincts and emotions as disclosed by psycho-analysis), but also tends to modify certain general evolutionary ideas, particularly in constituting an impressive argument against the Spencerian idea that evolution is synonymous with progress and in thus leading us back to Darwin's original non-teleological conception. On the other hand he thinks that a social psychology built on psycho-analytical theory would have only a passing value, lasting until our sexual customs were brought more into relation with biological facts. In this he evidently overestimates social prejudice as a cause of repression and does not realise how deeply seated the causes of repression are.