Why do African Americans have big lips?
First of all African Americans aren’t the only ones with big lips. Most people who’s ancestry is that from a warmer climate would develop larger lips. African Americans are descendants of Africans where summer and the sun are constant. Larger lips are one of the evolutionary ways of dealing with this kind of climate.
With evolution our bodies slowly change to help us survive whichever climate we live in. Over many years, African’s and even Latino’s have developed ways of dealing with this, including larger nostrils, lips and darker skin.
When it is hot outside we breathe more to cool ourselves and get more oxygen. A larger nasal passage helps get more air for faster cooling. Larger lips allow more surface area for the cool air that’s inhaled and exhaled to cool the body faster. In an African climate this would give a great advantage.
Dark skin is also an evolutionary trait from this region of the world. Dark skin comes from the body developing a melanin pigment that helps the body absorb UV rays from the sun.
There are many stereotypes as to why Africans (not just African Americans) have big lips. Though most of these are just derogatory jokes toward their race, some of them are true based on more air over a surfaces allows for faster cooling.
Big lips, big noses and dark skin are all just ancestry. That ancestry has been developed to help them deal with the extreme heat that they have faced for thousands of years in Africa (and other warm climates).