Consciousness, Self-Consciousness, Society

Marx-Engels assert of Consciousness that it is of "other persons and things outside the individual who is growing self-conscious".  So, in other words, they identify Consciousness and Self-Consciousness, as opposed to, say, Hegel, who distinguishes them.  And, therefore, their concept is one that is essentially social, in significant contrast with, notably Descartes',  However, the concept of Self-Consciousness as essentially social is not exclusive to Materialism--neither Kant's, in his Refutation of Idealism, nor Heidegger's Being-in-the-World, each implicitly social, is Materialist.  Regardless, nothing in Marx-Engels' formulation of Self-Consciousness includes Practice qua Purposiveness; rather, it entails only association with others, which can be for its own sake.  Hence, rather than as another means to the survival of the individual, Self-Consciousness can also be interpreted as a manifestation of a Formal Species-principle, the main function of which is to integrate its otherwise randomly compresent members.