Evolutionary psychology is the branch of psychology that understands the mind as a product of biological evolution. Just as the organs of our bodies evolved specific functions over time, so did the human mind. Its functions — fear responses, emotional understanding, our deep sociality — are studied as adaptations shaped by our evolutionary history rather than as blank-slate learning. The explanatory logic is straightforward: a cognitive mechanism exists because, on average, it helped our ancestors survive and reproduce. Consider the classic case. You see a stick in tall grass and you flinch, heart rate climbing, fight-or-flight overriding rational thought before you've consciously decided anything. That over-reaction is the point. In our evolutionary past it was far cheaper to mistake a stick for a snake and live than to mistake a snake for a stick and die. The mind is tuned to err on the safe side, not the accurate one.

More recent work extends this approach to culture and religion. The beliefs and behaviors that feel most distinctly human can be explained by looking at how our cognitive systems evolved — and the same triggered mechanisms help explain how emotional information spreads across social networks, online and in person.