His afterword adds that '[t]he crucial commodity for the production of surplus value, labour power, is itself produced and reproduced under social relations over which capitalists have no direct control. … though labour power is a commodity, the labourer is not' (1982: 447).Much of the value extracted by capitalist firms may have its ultimate origin here, in the domestic care and productive kindness of familial human relations. We "reproduce laborers" -- i.e. raise children -- through all sorts of uncompensated labor, and we sustain friendships and meaningful relationships through similar work. We work on friendship-building projects that have the side effect of yielding commoditizable goods and services.
This raises the question whether, in addition to having a use-value and an exchange-value, labour-power has a value that is set by the labour theory of value. The 'value theory of labour' denies this because labour-power is a fictitious commodity, not a real commodity. Seen in this light, the wage, the bundle of commodities that it can buy, and the role of non-commodified goods and services (as provided, for example, through domestic labour and/or collective consumption) are determined in the first instance through a combination of class struggle and the interest of certain capitals in expanding the market for consumption goods (cf. Grundrisse: 409, cited Harvey 1982: 49).
Capitalism finds ways to extract the productivity of sharing, caring and collaboration by alienating it from the relations in which it is situated, and by driving us to live in conditions that either deny opportunities for such caring and sharing or make them more readily exploitable. This seems to be one of the functions of social networks.