behavior
Explanation
The Joke
The comic shows two older academics (possibly professors) having a debate about the nature of human behavior. One argues that behavioral genetics is "not a real science" because it tries to reduce the complexity of the human brain to overly simplistic models. The other counters that the "true science of mind" is empirical psychology, which can detect how a person's entire sense of self can be predetermined by subtle environmental cues and suggestions. A student observing the argument asks, "Why are they always too aggressive or too cold?" -- implying that academics in these fields tend to be extremists in their positions.
The comic satirizes the long-running nature vs. nurture debate in the behavioral sciences. One side dismisses genetics as reductionist; the other side dismisses it in favor of psychology's emphasis on environmental influence. Both speakers present their own field as the "real" science while dismissing the other, reflecting the tribal turf wars that can occur between academic disciplines.
The Humor
The humor works on multiple levels. First, it is funny that both scientists are guilty of the same intellectual arrogance they accuse the other side of -- each claims their discipline is the "true" science while dismissing a neighboring field. Second, the student's observation that they are "always too aggressive or too cold" is a meta-joke about how scholars in debates about human behavior ironically demonstrate poor interpersonal behavior themselves. The punchline undercuts both academics by suggesting that the people who study human behavior professionally are somehow the worst at exhibiting balanced behavior in practice.