Darwin did plagiarise Matthew's prior published theory, name for it and highly idiosyncratic explanatory examples

 We know there is an overwhelming abundance of evidence that Darwin plagiarised Patrick Matthew's prominently prior published (1831) theory of macroevolution by natural selection. The images below, regarding this inconvertible fact (hated by wilfully ignorant, fact denial, Darwin fanatics everywhere), are from my book Nullius in Verba: Darwin's greatest secret

The psychologist and Senior Lecturer in psychology, sociology and criminology Andy Sutton (who is no a relative of mine) explains the significance of the overwhelming evidence for Matthewian knowledge contamination of Darwin's brain in his Amazon book review of Nullius: 

"… in an investigation of this kind, in the absence of Darwin’s fingerprints on a copy of Matthew’s book, a circumstantial case has to be built which appeals to concepts such as ‘preponderance of evidence’ or ‘reasonable doubt’. This is not to say the case is imagined – the case is built on verifiable evidence.

I would ask readers to imagine themselves as a juror. Suppose Emma in village A invents the wheel. Several people in villages B, C, D and E see the wheel and know about it. There are paths from all those villages to village F that are known to be in use. Daniel in village F later, apparently independently, invents the wheel. Not only that but Daniel’s wheel, which is of course the same concept, is made of the same materials and has similar features to Emma’s wheel. Daniel has been friends with, and talked to, some of the people in those other villages, who we know have seen the wheel. They know he is working on a wheel concept. When challenged by Emma, Daniel claims nobody in his sphere knew about her wheel, but this can be shown to be false, ie they did know. Daniel is then credited with inventing the wheel. Members of the jury …

The wheel analogy isn’t perfect, but that is in essence the case that Dr Sutton builds, and he isn’t saying “might have read Matthew” or “might have known Darwin”, he is showing us irrefutable proof that you can see for yourself if you have internet access. There are other aspects to the argument which give further support, which you will find in the book.

So, I find the argument completely persuasive."

 And so we can be confident that the plagiarism happened. We can say that and back it up with the overwhelming evidence above, and even more besides, but without a smoking gun we cannot know exactly when or how the knowledge contamination happened. Irrational Darwin fanatics who insist that proper scholars must supply them with the evidence for exactly how and when the contamination occurred - for the other evidence it did happen be taken seriously by them - ignore the logic of their own hero when it comes to such questions of evidence:

Seven years after the publication of Matthew's (1831) book On Naval Timber and Arboriculture, in his Notebook E, (1838-1839) Darwin wrote:  

"It is one thing to prove that a thing has been so, & another to show how it came to be so." 

Leon Zitzer (2017) explains how members of the scientific establishment (excluding Darwin's understanding cited above) stupidly failed to understand that you do not have to prove how a thing happened to prove, beyond reasonable doubt, or prove on a balance of reasonable probabilities that a thing did happen:

"Mainstream scientists of the time deployed a phony outrage at the anonymous author of Vestiges of the Natural History of Creation, ridiculing him as an amateur scientist who did not understand science—a tactic that was so effective, it clings to him to this day. I call their outrage phony because what truly annoyed them about his work, which they dared not openly admit, was that in fact he had done a great job at assembling the evidence to prove that development or evolution was happening, meaning it was more probable than special creation. He put them to shame and they could not bear to admit it. The one aspect of their outrage that was not phony was how incensed they were that he would not go away. This truly upset them. Despite their attacks and intense loathing of him, his book went through ten editions by 1853 and kept getting better and better. Scientists were fuming." 

                            (from "A Short but Full Book on Darwin’s Racism" by Leon Zitzer)