How is it possible for only some races to have certain diseases or deformities like Sickle-Cell Anemia for African-Americans and Head Lice for Caucasians?
Some diseases are the result of adaptations to an environment. As it turns out, Sickle Cell Anemia is an adaptation to Malaria. If a person has a single copy of the Sicke Cell gene, he or she is protected against Malaria. If he or she has NO copies of the gene, he or she will die if exposed to Malaria. If he or she has two copies of the gene he or she will die from Sickle Cell Anemia. Malaria was fatal to pretty much everyone. The genetic mutation allowed about half of the population of the region to live. Today, we no longer have the threat from Malaria so now Sickle Cell Anemia becomes the problem.