Marx defined the concept of labor a real abstraction, being an abstraction always historically produced when "one thing appears as common to many, to all."
In a society where labor turned to be so widely articulated and diffused, to the point of becoming the prime reason of social wealth, it has been possible to embrace all the different working activities within a generic abstract labor, a labor sans phrase, uniform in quality and only different in quantity, the one which does not require anyone in particular to be performed.
This average labor is social by nature and present in every single activity as crystallised expression of a common social substance (gemeinschaftlichen gesellschaftlichen Substanz). In this sense, the use of the term generic, which derives from the greek substantive ghenos "race", "kind", "species" and the verb gignomai "coming into being", "generating" or "producing", results appropriate to indicate both an undifferentiated general quality of the species-being (Gattungsgwesen)  and the very idea of "life-activity", "giving rise" or "becoming".
Because of such abstractness and genericness, according to Marx social labor possessed an exchange-value that enabled its separation and calculability from the definite special form of the proper use-value. Value was nothing but the mere congelation of homogeneous human labor, of labor-power expended "without regard to the mode of its expenditure", being labor-power the potential aggregate of mental and physical capabilities "existing in the physical form, the living personality, of a human being".
Such a potential does not exists per se but only as a capacity (dynamis), as possibility of becoming indissolubly bound to the living being. For these reasons man could be defined a social individual,a twofold entity made both of singular determinations and general faculties, gradually attained through a process of "individuation" from an indefinite basin of generic existence.
This pre-individual realm, made of material and intellectual endowments, is constantly declined and actualised by each singularity in relation to its contingent circumstances. Therefore, the process of individuation does not exhaust in a single act or in a final balanced state but lies within an amphibious status of permanent struggle for adaptation and self-preservation: the unlimited human life-engendering aptitude.
Karl Marx. “The Method of Political Economy”, A Contribution to the Critique of Political Economy (Moscow: Progress Publishers, 1859); Karl Marx. Economical and Philosophical Manuscripts of 1844, (Moscow: Progress Publishers,1959), “Estranged Labor”, par. XXIV; Henry George Liddell, Robert Scott. A Greek–English Lexicon (Oxford: Clarendon Press, 1940);  Karl Marx. Capital. A Critique of Political Economy (Hamburg: Otto Müller Verlag, 1867) Volume I,6