Marxism and Human Nature

Marx anticipates Existentialism by proposing that humankind has no fixed Essence, i. e. has a mutable nature. Correspondingly, he argues that Socialism is only an historically contingent optimal mode of organization, since it is possible only subsequent to the attainment of a certain level of Industrial Capitalism.  However, he also conceives Socialism as, once estabilished, to be thereafter permanently optimal, which would seem to imply, correspondingly, that humankind has then, if not acquired an Essence, at least arrived at a thereafter immutale nature.  Now, in a likely effort to correct that apparent inconsistency, some Marxists have argued that perpetual Revolution is the ultimate goal.  However, they do not conceive that as entailing an eventual surpassing of Socialism, rather, that such persistence is required to preserve Socialism from unremitting threats, both external and external.  So, whether or not, according to Marxism, Humankind has a potential fixed nature, corresponding to which is a permanent optimal Polity, is uncertain.