>>10795743>spending so much time in the water over generations living on fish that they developed webbed handsOr maybe it was the incest, as finding a woman not related to you meant traveling through 100 miles of poisonous jungle with snakes, jaguars, flesh eating ants and electric eels.
On a more serious note the only similar thing I've heard is of some amazon tribes that develop prehensile feet from traveling through trees hunting monkeys and avoiding the dangers of the jungle floor. They only develop them as adults.