Mammals that make their own vitamin C can live 8 to 10 times longer than the age of their ______ maturity. While most plants and animals can produce their own vitamin C, humans cannot. Since guinea pigs cannot make their own vitamin C, like humans, they were one of the first ______ animals for testing purposes. In fact, testing guinea pigs helped discover what vitamin C was. It was the first vitamin to be manmade, produced in a factory and taken as a pill.