Like only black people have curly hair
Hair is actually one of the clearest markers of genetic ancestry. Black people have naturally curly hair. Pure white people do not. The only so-called whites with curly hair are those from groups like the Jews, Italians, and Spanish that only got their curly hair because of their black ancestry. DNA tests have proven that all these groups have large amount of African male ancestry (E1b1b). Same with the Eastern Europeans in the Balkans. Their male genetic ancestry is the same as East Africans.
Natural selection made it so that straight hair was more advantageous in the northern cold environments your people evolved in. You needed that long straight hair to cover your necks and warm you up. In Africa where its warm, we didn't need to evolve long hair to keep ourselves warm. So our hair curled so as to not cover our necks. But in Europe ya'll needed the hair to be straight so it could hang over your necks warming you up. Curly hair was only introduced into the modern European population by BLACK PEOPLE. That is why it is most prominent in the groups close to Africa like the Italians, Spanish, Balkans, and Jews (who migrated from Africa more recently than the rest of the European population). The DNA evidence of this is quite clear.
For comparison's sake, look at Eastern Asia. Most Chinese and Japenese have no recent African ancestry. Thus their hair is not curly at all. Its bone dry straight. Its almost impossible to find a East Asian (that isn't a Negrito) with curly hair. The same was true for Europeans before black people came up into Europe and mixed in with the population.