Modern evolutionary theory has brought the question of human exceptionalism back into our consciousness. From a scientific standpoint, researchers have discovered startling similarities between humans and animals (though the dissimilarities are often overshadowed). For some, "rational animal" no longer cuts it as a real distinction that makes humans special.
For John Calvin, the uniqueness of humans stems not from their rationality, but from their propensity to worship: "Therefore, it is the worship of God alone that renders men higher than the brutes, and through it alone they aspire to immortality."
This move, which happens relatively early on in the Institutes, is a significant one for Calvin's overall theology. The core of human sin is not strictly an intellectual malfunction, though it is that as well. It is that the human disposition to worship has been directed toward an improper object: an idol.
Hence Calvin's understanding of the knowledge of God: "Now, the knowledge of God, as I understand it, is that by which we not only conceive that there is a God but also grasp what befits us and is proper to his glory, in fine, what is to our advantage to know of him. Indeed, we shall not say that, properly speaking, God is known where there is no religion or piety."
While Aristotle thought man was a rational animal, Calvin considers him a worshiping animal. The law of human creation is that the sensus divinitatis impels us to seek its rightful object.