There is a group of instincts that care for the destinies of these elementary organisms which survive the individual being, that concern themselves with the safe sheltering of these organisms as long as they are defenceless against the stimuli of the outer world, and finally bring about their conjunction with other reproductive cells. These are collectively the sexual instincts. They are conservative in the same sense as the others are, in that they reproduce earlier conditions of the living substance, but they are so in a higher degree in that they show themselves specially resistant to external influences; and they are more conservative in a wider sense still, since they preserve life itself for a longer time. They are the actual life-instincts; the fact that they run counter to the trend of the other instincts which lead towards death indicates a contradiction between them and the rest, one which the theory of neuroses has recognised as full of significance. There is as it were an oscillating rhythm in the life of organisms: the one group of instincts presses forward to reach the final goal of life as quickly as possible, the other flies back at a certain point on the way only to traverse the same stretch once more from a given spot and thus to prolong the duration of the journey. Although sexuality and the distinction of the sexes certainly did not exist at the dawn of life, nevertheless it remains possible that the instincts which are later described as sexual were active from the very beginning and took up the part of opposition to the rôle of the ‘ego-instincts’ then, and not only at some later time. Let us now retrace our steps for the first time, to ask whether all these speculations are not after all without foundation. Are there really, _apart from the sexual instincts_, no other instincts than those which have as their object the reinstatement of an earlier condition, none that strive towards a condition never yet attained? I am not aware of any satisfactory example in the organic world running counter to the characteristic I have suggested. The existence of a general impulse towards higher development in the plant and animal world can certainly not be established, though some such line of development is as a fact unquestionable. But, on the one hand, it is often merely a question of our own valuation when we pronounce one stage of development to be higher than another, and, on the other hand, biology makes clear to us that a higher development in one particular is often purchased with, or balanced by, retrogression in another. Then there are plenty of animal forms the youthful stages of which teach us that their development has taken a retrograde character rather than otherwise. Higher development and retrogression alike might well be the results of external forces impelling towards adaptation, and the part played by the instincts might be confined in both cases to retaining the enforced changes as sources of pleasure.[18]