Three weeks after the question and still nothing worth upvoting. Looks like you are not interested in fonts which we today say to have "humanist characteristics" in modern typography terms. The given answers contain several of them.
As already said in the answers, the handwriting style line named Humanist in your script development image presents something which was developed in the first half of the 15th century - just before Gutenberg's metal type printing method conquered the book production. I have heard (maybe only a joke) that the mainstream Gothic lettering styles were too difficult to be red in dim indoor light with aged eyes. As a counter-action style "Humanist" was created by some respected handwriters who have just noticed that also they will get old.
See for ex. this:
These, of course, are modern font implementations of medieval letterings, but if they are even half-faithful for old book and official document lettering styles, it's easy to believe that something had gone wrong (btw. the text is unimnium).
I guess it was not at all easy to fix the problem. Substantial amount of talent and practicing is needed to develop a new handwriting style which looks fine, is easier to read and is at least as fast to write as the mainstream ones.
The inventor in addition must have a position where persons like The King and The Pope and their advisors bother to listen. But just that happened in early 1400's Italy (not as a state, but as an area of several strong and fast developing independent cities). There the conditions developed favourably for independent professionals. Suddenly they could start to create things as they wanted - at first for local potentates and soon even for the Roman Church. They earned enough to be able to make also some development research.
I believe the easier to read and simpler to write lettering style was not an exception. Some independent lettering professionals took good letters from obsolete styles, say Carolingian and created their own mixtures. Your line "Humanist" is trying to present just one such mixture which happened to be liked by some mighty enough secular and ecclesiastical potentates. Soon every lettering artisan had to learn it to get well paid jobs.
But notice: your image is a creation of one Wikipedia writer who says "this is my drawing based on several sources". It's well possible that the writer has picked a mixed bag of glyphs from different fonts to make a drawing that he hopes to explain things somehow, but without being a 100% historical fact in every detail. A fact would need images of old well known manuscripts or traceable snippets of approved scientific works.
As said in the answers, lettering style Humanist inspired people who created metal types for printing machines and even today some enthusiasts have developed computer font implementations of old lettering styles. It's difficult to find them. Serching in the web for "humanist font" brings to you something totally different than the line Humanist in your image. You'll get better results by checking old style which contain something of word Carolingian. At least this one has many glyphs which are quite the same as your example:
As you see, it's not 100% the same. I found it by browsing manually medieval fonts in a couple of font download websites (dafont, 1001 fonts). Unfortunately I cannot tell where one can purchase it legally and how it's licensed.