Over the years, a few people have questioned this version of events. In the early 1980s, two books, one written by Arnold Brackman and another by John Langdon Brooks, even suggested not only that there had been a conspiracy to rob Wallace of his proper credit, but that Darwin had actually stolen a key idea from Wallace to finish his own theory. These claims have been examined in detail by a number of scholars who have not found them convincing. Shipping schedules show that, contrary to these accusations, Wallace's letter could not have been delivered earlier than the date shown in Darwin's letter to Lyell.