The individual, as such, if he could live, would fulfill only one of the two fundamental requirements (needs) of existence:  alimentation—­that is to say, the selfish preservation of his own organism, by means of that primordial and fundamental function, which Aristotle designated by the name of ctesi—­the conquest of food.

But all individuals have to live in society because a second fundamental requirement of life imposes itself upon the individual, viz., the reproduction of beings like himself for the preservation of the species.  It is this life of relationship and reproduction (sexual and social) which gives birth to the moral or social sense, which enables the individual not only to be, but to co-exist with his fellows.

It may be said that these two fundamental instincts of life—­bread and love—­by their functioning maintain a social equilibrium in the life of animals, and especially in Man.

It is love which causes, in the great majority of men, the principal physiological and psychical expenditure of the forces accumulated in larger or smaller quantities by the consumption of daily bread, and which the daily labor has not absorbed or which parasitic inaction has left intact.

Even more—­love is the only pleasure which truly has a universal and equalitarian character.  The people have named it “the paradise of the poor;” and religions have always bidden them to enjoy it without limits—­“be fruitful and multiply”—­because the erotic exhaustion which results from it, especially in males, diminishes or hides beneath the pall of forgetfulness the tortures of hunger and servile labor, and permanently enervates the energy of the individual; and to this extent it performs a function useful to the ruling class.

But indissolubly linked to this effect of the sexual instinct there is an other, the increase of the population.  Hence it happens that the desire to eternize a given social order is thwarted and defeated by the pressure of this population which in our epoch assumes the characteristic form of the proletariat,—­and the social evolution continues its inexorable and inevitable forward march.

It follows from our discussion that while at the end of the eighteenth century it was thought that Society was made for the individual—­and from that the deduction could be made that millions of individuals could and ought to toil and suffer for the exclusive advantage of a few individuals—­at the end of our century the inductive sciences have demonstrated, just the opposite, that it is the individual who lives for the species and that the latter is the only eternal reality of life.

There we have the starting-point of the sociological or socialist tendency of modern scientific thought in the face of the exaggerated individualism inherited from the last century.

Modern biology also demonstrates that it is necessary to avoid the opposite excess—­into which certain schools of utopian socialism and of communism fall—­the excess of regarding only the interests of Society and altogether neglecting the individual.  An other biological law shows us, in fact, that the existence of the aggregation is the resultant of the life of all the individuals, just as the existence of an individual is the resultant of the life of its constituent cells.