The narrator explains that in fifteenth-century civilizations in Africa, different hairstyles could signify wealth or mourning, and hair in general was considered a passageway for spirits into the soul. When Africans were sold into slavery, this history disappeared. Slave traders shaved their captives' heads, depriving them of their identity. After slavery ended in the US, African Americans strove to have hair that was as European as possible: straight and smooth. People developed straightening products, and now, the black hair care market is worth more than a billion dollars per year.
It's important to recognize that hair was (and still is) a symbol for the many different ways that people are connected to each other (like mourning another person) and to their gods. Once again, the novel highlights how everyone and everything is connected across time and space. Similarly, the desire for European hair shows that having a very visible connection to Europeans is a way to connote power and acceptability.
However, the African American community has constantly debated the question of hair. The narrator says that when Natasha decided to wear an Afro, she didn't make that decision because she knew the history, and she did it even when Patricia said that Afros make women look unprofessional. Patricia's arguments are rooted in a fear that Natasha will be hurt by a society that fears blackness. In addition, she also saw Natasha's Afro as a rejection of her—though the narrator insists that decisions like Natasha's are ones that all teens make. Natasha's Afro took three years to grow in, and she did it because it's beautiful.
Notice Yoon's choice of language at the end of the chapter—she insists that Afros are beautiful, not that just Natasha thinks so. This is a very overt way to remind the reader that while world cultures are all connected, they must also be thought of as equally rich in different ways. Essentially, though it acknowledges the connections between cultures, it also works to celebrate difference.