"These two years and three months were the most active ones which I ever spent, though I was occasionally unwell, and so lost some time. " Charles Darwin, Autobiography
Darwin is describing the two years after coming back from the five-year voyage. He had collected an enormous amount of material and was sitting with the experts going through them and preparing various manuscripts. There's no further training for any other occupation than being a scientist.
But Darwin is rich. He is supported by his father and later by investments and the sale of his books.