More's a Poppering: Psychohistory and Psychologism

 ‘It is not the consciousness of man that determines his existence—rather, it is his social existence that determines his consciousness.’

Popper, Karl R.. The Open Society and Its Enemies (Princeton Classics) . Princeton University Press. Kindle Edition. 

I am back to Popper after a long literary diversion.  By contrast with his disdain for Hegel, Popper clearly feels some affinity for Marx, whom he seems to regard as a good scientist brought down by the unfortunate disease of historicism - the belief that history unfolded by ineluctable laws as inevitable as the motions of the planets.  One thing he likes about Marx is his insistence on the autonomy of sociology as in the epigram quoted above.  He contrasts this with J. S. Mill's notion that society is a product of human nature and psychology - psychologism to Popper. For Popper, Mill too is a victim to "historicism" in Popper's view.

Popper devotes a chapter to the conflict, but to me it is bogus one.  Ir seems obvious, at least from the standpoint of contemporary anthropology and archaeology, that society and human nature evolved  together, with social and cultural evolution dramatically taking first place in the last ten thousand years as technology radically transformed the world.

Perhaps the most important criticism of psychologism is that it fails to understand the main task of the explanatory social sciences. 

This task is not, as the historicist believes, the prophecy of the future course of history. It is, rather, the discovery and explanation of the less obvious dependences within the social sphere. It is the discovery of the difficulties which stand in the way of social action—the study, as it were, of the unwieldiness, the resilience or the brittleness of the social stuff, of its resistance to our attempts to mould it and to work with it.

Popper, Karl R.. The Open Society and Its Enemies (Princeton Classics) . Princeton University Press. Kindle Edition. 

A Popperian digression on what he calls the Conspiracy Theory of History:

Conspirators rarely consummate their conspiracy.

Popper, Karl R.. The Open Society and Its Enemies (Princeton Classics) . Princeton University Press. Kindle Edition. 

 I think that he is wrong, although I wouldn't exactly call the actions of interest groups that steer society to be conspiracies, since they are rarely hidden.  At almost every point of history small groups of individuals have used property rights to ensure that they enjoyed the fruits of others labors.  This "conspiracy" if you like originated shortly after the invention of agriculture and has persisted in various forms ever since.

However, I can't say that I really followed Popper's  argument as to why Mill's theory was an example of historicism.