When Darwin visited the tropical rainforest he was amazed by the diversity of the life there. Darwin wrote about "the general luxuriance of the vegetation . . . the elegance of the grasses, the novelty of the parasitical plants, the beauty of the flowers, the glossy green of the foliage . . . " He wondered how the life had become so complex and diverse. Darwin saw organisms chasing each other, eating each other, trying to find food and water and other things that they needed, and he started thinking about how every organism struggles for life.