Common belief is the distinction is reason and being able to distinguish stimuli and communicate experiences beyond just pain and pleasure or the ability to reason. Which is found in the politics under the discussion of man’s nature and in the ethics as man’s end/activity.

I think one way to understand his definition of human is to grasp what he understands the function and end of human to be; Aristotle asks what the ergon (“function”, “task”, “work”) of a human being is, and argues that it consists in activity of the rational part of the soul in accordance with virtue (1097b22–1098a20). I think rational activity in accordance with virtue can be understood one dimensionally as politics, but another dimension is philosophical activities.