Read this: A more recent study by science historian John van Wyhe has determined that the idea that Darwin delayed publication only dates back to the 1940s, and Darwin's contemporaries thought the time he took was reasonable. Darwin always finished one book before starting another. While he was researching, he told many people about his interest in transmutation without causing outrage. He firmly intended to publish, but it was not until September 1854 that he could work on it full-time. His estimate that writing his "big book" would take five years was optimistic.

What was Darwin's original estimate for the amount of time his book would take to write?
What is the answer? (If it cannot be answered, return "unanswerable")
five years