Why do black people have nappy hair?

People predominately from Western Africa (not the entire continent of people have extra kinky hair - Eastern Africans like Ethiopians for example) have extra kinky hair as a defense mechanism against the sun. Same reason our skin is so dark.

Darker skin has more melanin (sp. sorry) and more concentrated this is, the more protection you have against the sun. That's not to say you are immune, but if you are living in an extremely hot climate like West Africa, and you're living before sunscreen was invented, you have way more of an advantage if your skin contains high levels of melanin.

Hair on the top of the head that coils and coils and is very dense and close to the scalp protects your scalp/head from the sun as well. So when you're out gathering food and water all day and/or hunting, the sun won't fry your brain. So the original man, because of where he was located, evolved to have extremely dark skin and extremely coily/kinky hair to protect him from the sun's exposure.

Thousands of years ago, as people started to migrate and populate the world, they evolved or changed, just like any other animal, to adapt to their environment. Those who moved to much colder climates needed more vitamin D in their skin and did not require or need so much melanin so they paled. Their hair got less kinky so it could help warm them as it was easier for the hair to show length the straighter it is.

If you look at the planet, you can pretty much see that people look the way they look in response to their environment. It's not perfect (because of other nations conquering other nations, producing different looking people than the original people that were there) because the adaption takes thousands of years, but that's why people look different in a nutshell. Once you know this it really makes racism look even more ridiculous.