What is the speaker’s mainly discussing?

A lot of people think that cultural anthropology is just about studying the special and strange aspects of a society, but anthropologists are also interested in the aspects of life that seems so ordinary that the people in the society think they’re not significant. Let me give you an example, I see lots of T-shirts here in class today, but you probably don’t think of them as an important part of your culture, but anthropologists could learn a lot about the culture of the US just by studying the T-shirt. For one thing, T-shirts are a mark of how casual clothing has become in America. No one was quite sure where they came from, but the T-shirt first become popular in this country as an under shirt for sellers in the 1940s. Then in the 1950s, it became a sign of rebellion for teenagers to wear this white under shirt by itself, not under anything. By the 1960s and 70s, T shirts have become accepted as part of the uniform views. You could even say that they came symbolized that generation’s attitude towards informality and all things, including dress. On another aspect that anthropologists would find interesting is that T-shirts are used to express personal opinions. Look around this room, you know who likes watch TV show, who went where on vacation, who belongs to what organizations on campus. All of these aspects of our culture are printed on your T-shirts. OK, I want to stop for a minute and ask you to try to write down five different conclusions you could reach about American culture from just the T shirts in this classroom.