there would be no consequence of losing the ability to make vitamin C since she already ate foods that contained it. (What foods contain a lot of vitamin C? Citrus fruits. And where do citrus fruits mostly grow? Tropical rainforests. And where do most primates live? Bingo.) The reason that the ancestors of primates could tolerate a mutation in the GULO gene was that, with plenty of vitamin C in their diets anyway, scurvy wasn’t an issue. Since that time, primates—with the exception of humans—have pretty much stuck to rainforest climates.
