Among the options listed, "disease" would generally not be a direct cause of natural selection itself; rather, it is often a result that can affect an organism's survival and reproduction.
Natural selection typically acts on traits that enhance an organism's fitness in its environment, such as camouflage, which can provide a survival advantage, or weakness and mental impairment, which can be detrimental. In contrast, disease can impact populations in various ways but isn't a trait that is selected for or against in the same way.
So, the answer is disease.