[15] The following considerations would support the view expressed above. Man, too, is an animal with an unmistakably bisexual disposition. The individual represents a fusion of two symmetrical halves, of which, according to many authorities, one is purely male, the other female. It is equally possible that each half was originally hermaphroditic. Sex is a biological fact which is hard to evaluate psychologically, although it is of extraordinary importance in mental life. We are accustomed to say that every human being displays both male and female instinctual impulses, needs and attributes, but the characteristics of what is male and female can only be demonstrated in anatomy, and not in psychology. Where the latter is concerned, the antithesis of sex fades away into that of activity and passivity, and we far too readily identify activity with masculinity and passivity with femininity, a statement which is by no means universally confirmed in the animal world. The theory of bisexuality is still very obscure and in psycho-analysis we must be painfully aware of the disadvantage we are under as long as it still remains unconnected with the theory of instincts. However this may be, if we assume it to be a fact that each individual has both male and female desires which need satisfaction in his sexual life, we shall be prepared for the possibility that these needs will not both be gratified on the same object, and that they will interfere with each other, if they cannot be kept apart so that each impulse flows into a special channel suited for it. Another difficulty arises from the circumstance that so often a measure of direct aggressiveness is coupled with an erotic relationship, over and above its inherent sadistic components. The love-object does not always view these complications with the degree of understanding and tolerance manifested by the peasant woman who complained that her husband did not love her any more, because he had not beaten her for a week.