Capitalism, Marxism, Nominalism

According to Nominalism, the 'human race' is no more than its individual members, i. e. there is no 'human species' that is distinguishable from that manifold.  Likewise, in Nominalism, no group concept, e. g. Nation, Family, Society, Class, etc. is distinct from its members.  Now, Capitalism is plainly a Nominalist system, in which any group is no more than an association of members.  But, despite its focus on groups, especially on Class, Marxism never abandons Nominalism, distinguished from Capitalism by conceiving individuals as related dialectically, rather than associatively.  So, one challenge to it, as much as to Capitalism, is to explain why the respective mode of relation is specific to certain entities, or, in other words, why either kind of relation does not extend outside of the species.  Such circumscription suggests that the behavior of its members is, at least to some extent, governed by a Species-principle that transcends the members to which it applies.