Antiphon on human nature.

"[Those born of illustrious fa]thers we respect and honour, whereas those who come from an undistinguished house we neither respect nor honour. In this we behave like barbarians towards one another. For by nature we all equally, both barbarians and Greeks, have an entirely similar origin: for it is fitting to fulfil the natural satisfactions which are necessary to all men: all have the ability to fulfil these in the same way, and in all this none of us is different either as barbarian or as Greek; for we all breathe into the air with mouth and nostrils…"

Antiphon of Rhamnus (B.C. 480-411)
Quoted in Untersteiner, p. 252

The astute will rightly appreciate the precedence of Antiphon (ironically executed for supporting the anti-democratic coup of B.C. 411) whose observation underlies those formed by Hobbes, Locke, Rousseau and the US Declaration of Independence among others.