[See here for all my 13 or so posts on Pattrick Matthew and plagiarism claims made on his behalf.]for example, here).
Nevertheless, Mike Sutton tries to sell that standard as a simple litmus test and claims to have proven that Charles Darwin and Alfred Wallace plagiarized Patrick Matthew beyond a reasonable doubt.
"The accumulation of weighty new evidence presented in this book proves beyond all reasonable doubt that both Wallace and Darwin were both indirectly influenced by others who read NTA [On Naval Timber and Arboriculture] and also directly influenced by reading NTA themselves, before either penned a word on the same subject." (Sutton 2014, p. 14)How does this weighty and new evidence prove the plagiarism of Darwin and Wallace? By simply counting how many people known to them have read Matthew (1831). I will ignore a number of other people identified by their use of what Sutton regards as 'Matthewisms.' Sutton is satisfied with seven scholars belonging to the social circle of Darwin and Wallace and three of them playing what he calls 'pivotal roles' in their scientific career.
The fact that they cited Matthew (1831) suffices for Sutton to conclude:
"Consequently, it does not matter whether or not Darwin or Wallace read the works of Loudon (1832), Chambers (1832) and Selby (1842) that cited Matthews’s book. Moreover, it does not matter whether or not it can be established that Loudon, Chambers and Selby, or those such as Blyth, and Wallace, whose pre-1858 work on evolution Loudon and Selby respectively edited and published, particularly understood the full details and implications of Matthew’s discovery. Because the fact of the matter is that Loudon, Chambers and Selby all read Matthew’s book that contained those very ideas."That's neat. It neither matters whether Darwin and Wallace actually read the works citing Matthew (1831) nor whether the scholars citing Matthew (1831) actually received the idea of natural selection from their perusal and transported it in their own writings. The simple numbers add up to prove beyond a reasonable doubt that Darwin and Wallace have plagiarized Matthew.
As Sutton's litmus test is so simple, simplistic even, you can check its efficiency yourself. Think of books that you have on your must-read list for a long time, but never got round to read. Now do a survey among your friends and acquaintances, how many of them did read it. If three close friends and seven acquaintances read it, you have also read it beyond any reasonable doubt. Your conviction of not having done so is unreasonable. In fact, if you ever use something you heard someone say about that book on a party, you are convicted of plagiarism!