Anthropology has many sub-specialties, one of which is cultural anthropology. Generally speaking, anthropology is the study of humans, but more than that, it studies how they interact with each other and their environment. A background in anthropology benefits an author because that knowledge can be used to make stories feel more real.
Cultural anthropology looks more closely at the differences between people and their cultures. Cultural anthropologists study how the culture shaped the world around them. For example, a cultural anthropologist would examine how Jewish and Muslim cultures are alike and different, how religion shapes everyday life within the culture and how those in the culture align their religion with their world view.
Another example of cultural anthropology could be a study of how people of certain localities may have different ideas about what foods are the best, or which sports teams one should root for. Everyone has a favorite food, yes, but certain cultures may have full menus of foods that are perceived as better than others. Sports teams tend to have fans that follow them no matter if they are home or on the other side of the globe. The abundance of sports bars shows just how much people enjoy being part of team culture.
Studying how people interact can inform an author’s craft and help the writer further explore the relationships of the characters. If you have characters that devoutly follow certain religions then there could be conflict between them because of the differences. Characters could come together over a shared meal and learn something about the other’s past because they both like pizza, but only deep dish! The characters may be fans of sports teams, and shouting at each other across the bar, only to realize they both like the same niche beer–and that they have more in common than they thought. Understanding how different cultures express themselves in the world around them allows for a more developed character and a better book for you!