"While machinery is the most appropriate form of the use value of fixed capital, it does not at all follow that therefore subsumption under the social relation of capital is the most appropriate and ultimate social relation of production for the application of machinery." http://www.marxists.org/archive/marx/works/1857/grundrisse/ch13.htm#p690
"...[T]he accumulation of the skill and knowledge -scientific power- of the workers themselves is the chief form of accumulation, and infinitely more important than the accumulation -which goes hand in hand with it and merely represents it- of the existing objective conditions of this accumulated activity. These objective conditions are only nominally accumulated and must be constantly produced and accumulated anew." [Theories of Surplus Value part III pages 266-267, translated by Emile Burns, Moscow, 1963-71]
Thus we may say that surplus-value rests on a natural basis; but this is permissible only in the very general sense, that there is no natural obstacle absolutely preventing one man from disburdening himself of the labour requisite for his own existence, and burdening another with it, any more, for instance, than unconquerable natural obstacle prevent one man from eating the flesh of another. No mystical ideas must in any way be connected, as sometimes happens, with this historically developed productiveness of labour. It is only after men have raised themselves above the rank of animals, when therefore their labour has been to some extent socialised, that a state of things arises in which the surplus-labour of the one becomes a condition of existence for the other. At the dawn of civilisation the productiveness acquired by labour is small, but so too are the wants which develop with and by the means of satisfying them. Further, at that early period, the portion of society that lives on the labour of others is infinitely small compared with the mass of direct producers. Along with the progress in the productiveness of labour, that small portion of society increases both absolutely and relatively. Besides, capital with its accompanying relations springs up from an economic soil that is the product of a long process of development. The productiveness of labour that serves as its foundation and starting-point, is a gift, not of nature, but of a history embracing thousands of centuries. http://www.marxists.org/archive/marx/works/1867-c1/ch16.htm
"From the standpoint of a higher economic form of society, private ownership of the globe by single individuals will appear quite as absurd as private ownership of one man by another. Even a whole society, a nation, or even all simultaneously existing societies taken together, are not the owners of the globe. They are only its possessors, its usufructuaries, and, like boni patres familias, they must hand it down to succeeding generations in an improved condition." http://www.marxists.org/archive/marx/works/1894-c3/ch46.htm