Sickle cell is not found only in blacks. Although rare, it has been found in others. When I was a boy, it was said that only blacks get it and that it only manifests in men although women can pass it on genetically. We now know that this is all hooey.

Sickle cell is not the result of race but on natural selection. One component of the red blood cell is different than what is found in normal blood cells which is what causes the sickle shape. In West Africa, where malaria has always been a major health threat, it was dicovered that sickle cell fights off malaria. Malaria is a bacteria that attacks red blood cells but cannot tolerate the sickle cell and hence once sickle cell made its way into the gene pool, it stuck around because it is actually beneficial.

Unfortunately, it can also be a horribly painful ailment to offspring born of parents that both carry it. If only one parent carries it, it's not likely to cause problems in the children.

If sickle cell were race-related, we would expect blacks in America, descendants of West Africans mostly, to have it in as high a number as ever. The reality is that it has declined significantly in the U.S. which is what we'd expect to see if it were merely a product of natural selection. Once the cause of the proliferation of sickle cell, malaria, is no longer a factor in people's lives, it begins to recede from the gene pool. Hence, it is not race-driven.