I am saying there have been many frauds that have been caught.
Interestingly, to the best of my knowledge, there haven't been all that many biologists (I can only think of examples like the mammoth DNA scandal awhile back) who've done something like this. And they have ALWAYS been caught - usually really quickly. As nator mentioned, one of the first things that happens with a new discovery or idea is that everybody else in a relevant or related subdiscipline tries to either replicate the data (through observation or experimentation), or tries to find fault with the idea (along the lines of "this is pretty out there, is there a better explanation for what was observed?"). Why do you think things like the Mungo Lake data is/was so controversial? And not really accepted by the specialists? Because sample contamination is a better explanation for the really odd results than a whole new theory of human origins. (If you don't know the story, I can give a brief precis).
How many are there that have not been caught.
Given what I know of how the peer-review process in biology works, not many if any at all. We have LOTS of controversies, competing ideas, "battles of the data", arguments over interpretations, etc. However, that is the sign of a healthy science in action, not fraud. It took Margulis ten years (or thereabouts, I don't remember exactly) to get the idea that some cellular organelles in eukaryotes may hve been derived from symbiosis rather than developing over time via RM/NS. And she had really
good data. It's something of a truism in science that the more radical or novel the claim, the more scrutiny it will undergo - and the more vociferous the arguments. Doesn't leave a lot of room for somebody trying to sneak falsified data or an agenda-driven idea into the mix.
Do you have any specific examples in mind - in biology, 'cause that's what evolution is all about - or is your contention just a sort of general comment based on supposition, or something someone mentioned to you in passing?