Cystic fibrosis (CF) is a condition affecting secretory glands, such mucus and sweat glands. People with CF produce a thick sticky mucus which leads to a wide range of problems, including digestive issues and greater susceptibility to lung infections.
Males with CF are typically infertile. People with CF historically had a short lifespan, although people are now living longer as treatments improve. CF is caused by a mutation to the CFTR gene, which codes for a protein that transports chloride ions across the cell membrane.
In the U.S., the condition occurs in up to one of every 2,500 newborns of European decent. Only one in 17,000 African Americans and one in 31,000 Asian Americans are affected.
Which of the following hypotheses could explain the increased prevalence of CF in European populations?