If evolutionism is true, where are the one-eyed giants?

Evolution is based on traits of one species being passed along or dying out. First of all for there to ever be one eyed giants there would have to be a mixing of some crazy mutations in the human race, then if that happened what are the chances of this species surviving. If the traits do not help the species survive more than it did previously it would die out because there would be no need in nature for a one eyed giant. Please find out the information before asking a question