[Sidenote: Both greater integration and greater differentiation of society is thus secured] Under the last heading (7) we saw that the repression of incest would on the whole lead to the greater integration of human society through a more developed gregariousness and the establishment of firmer ties of interest and affection between the individual and the community. Under the present heading we have seen that the repression of the incest tendencies would also lead to greater differentiation through a more thorough development of individual characters, abilities and differences. If, with Herbert Spencer, we agree that the progress of society (like evolution generally) involves both integration and differentiation, it is easy to see how the inhibition of the tendencies to incest may have thus contributed in two distinct but complementary ways to the advance of human civilisation. (9) Westermarck, as we saw above (3), in endeavouring to account for the origin of incest horror, drew attention to the aversion to sexual intercourse between those who had lived together from early youth (a class of persons which usually, of course, includes the closer blood relatives). While we must disagree with Westermarck in his implicit denial of the underlying attraction between these persons--an attraction which makes the aversion in question to a large extent nothing more than a reaction against the desire for intercourse between them--it is nevertheless possible that the study of this wider aversion may throw a few rays of fresh light upon the narrower incest aversion with which we are concerned. [Sidenote: Among those who live together sexual reactions are inhibited by non-sexual]