Google's John Mueller said in a webmaster hangout that Googlers, at many levels, not just the elite set at the top, can debug the search algorithm. He said "Also the meta question here does anyone really know how the algorithm works. And that is something where we do have a lot of people in search quality that are able to debug pretty much any query."
This was at the 43:29 mark into the video, where he said this. He said that not only an "elite set of priests somewhere in Mountain View" are able to do this but at many levels within Google. He added that even Gary Illyes from Google has done this and continues to debug issues with search. He said "Gary has spent a lot of time on as well and he's been working on some of these search things too."
Here is this video where John said this:
Gary confirmed this in a video with Aleyda Solis at the 2:45 mark where he said "I work a bit in infrastructure, search infrastructure, but there I do coding mostly, like I am changing things and I am also doing lots of debugging, like ranking debugging when something looks fishy. Like someone reports something."
Here is this video where Gary said this:
So there you have it, even though Google has told us before they understand their algorithm and machines wont take over - this shows humans at Google can debug it. One example of Gary doing this was with the rel=prev/next issue but there are many more.
Forum discussion at YouTube Community.
