The Sickle Cell Trait, a heterozygous phenomenon, is called a selective polymorphism. What this means is that it confers a genetically derived protection to inhabitants of areas where malaria is endemic. The malarial parasite does not do well in sickle cells for a variety of reasons. This protection is, however, far outweighed by the disadvantages of having Sickle Cell Disease, where there are too many sickle cells. One is said to be homozygous for the trait. This becomes injurious to the individual himself/herself. Now consider individuals inhabiting hostile environments for centuries and surviving because of certain personality traits and social behaviours. This too could foster the creation of a selective polymorphism. It won’t be a point mutation like Sickle Cell Disease, therefore it may not be easily mapped. Yet consider brain changes that occur over time to accommodate the survival of future generations, genetically-derived brain changes. If those changes become amplified by consanguinity, this may lead to an entity that no longer benefits from such traits. This would also occur if the hostile environment now becomes ameliorated by whatever means and no longer exists except in the minds of its survivors. This then becomes a social polymorphism that has outgrown its usefulness, leading to pain, suffering and disability.
You don’t have to agree. You just have to consider…