they remained on friendly terms for the rest of Darwin's life. Over the years, a few people have questioned this version of events. In the early 1980s, two books, one by Arnold Brackman and another by John Langdon Brooks, 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 and found unconvincing by a number of scholars. 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. Defence of Darwin and his ideas After Wallace returned to England in 1862, he became one of the staunchest defenders of Darwin's On the Origin of Species. In an incident in 1863 that particularly pleased Darwin, Wallace published the short paper "Remarks on the Rev. S. Haughton's Paper on the Bee's Cell, And on the Origin of Species". This rebutted a paper by a professor of geology at the University of Dublin that had sharply criticised Darwin's comments in the Origin on how hexagonal honey bee cells could have evolved through natural selection. An even longer defence was a 1867 article in the Quarterly Journal of Science called "Creation by Law". It reviewed George Campbell, the 8th Duke of Argyll's book, The Reign of Law, which aimed to refute natural selection. After an 1870 meeting of the British Science Association, Wallace wrote to Darwin complaining that there were "no opponents left who know anything of natural history, so that there are none of the good discussions we used to have". Differences between Darwin and Wallace Historians of science have noted that, while Darwin considered the ideas in Wallace's paper to be essentially the same as his own, there were differences. Darwin emphasised competition between individuals of the same species to survive and reproduce, whereas Wallace emphasised environmental pressures on varieties and species forcing them to become adapted to their local conditions, leading populations in different locations to diverge. The historian of science Peter J. Bowler has suggested that in the paper he mailed to Darwin, Wallace might have been discussing group selection. Against this, Malcolm Kottler showed that Wallace was indeed discussing individual variation and selection. Others have noted that Wallace appeared to have envisioned natural selection as a kind of