Sympathy, Reason, Species-Principle

Several significant features of Kant's system are Rationalist counterpoints to some Hume's Empiricist-Sentimentalist concepts, notably that of Causality, and that of the I.  Likewise, whereas Hume's Universal principle is Sympathy, Kant's is Reason.  However, Kant cannot match Hume's characterization of Sympathy as a Species-principle.  For, according to the Groundwork, there exists at least non-Human Rational being, which he chatacterizes as the "head" of the Kingdom of Ends, a likely allusion to his deity.  Nor can easily respond to Hume by simply jettisoning that allusion, since there is nothing in his concept of Reason that distinguishes humans from any other entity, a generality that is a characteristic of Spinoza's concept of Reason, as well.  So, if there is a Rationalist Species-principle, it is unclear how it might be constituted.