In this question, one certainty is that the opening sentence will neither be in position 1 nor in position 4 because the given sentence is neither introductory nor concluding. It fits well in either position 2 or 3. The sentence states: "When people socially learn from each other, they often learn without understanding why what they’re copying—the beliefs and behaviors and technologies and know-how—works." It goes on to mention, "They tend to home in on who seems to be the smartest or most successful." This implies that people often learn without understanding why or what they are copying, and they tend to focus on those who appear to be the smartest. Position 2 is a better fit than position 3.