The animal duality in this metaphor calls to mind Plato's charioteer, in chapter 6 of The Republic, who drives a white horse and a dark horse.

The white horse symbolizes the noble and virtuous aspects of the soul, associated with reason and intellect. This horse represents the disciplined and controlled parts of human nature.

Conversely, the dark horse symbolizes the base and irrational aspects of the soul, driven by desires and appetites. This horse represents the untamed and passionate aspects of human nature, often leading to impulsive and reckless behavior.

And in the metaphor, the charioteer himself represents the rational part of the soul, guiding and directing the chariot.