“May have?” Since when did “may have” become science? Why didn’t all monkeys and apes evolve? This is just another theory. They haven’t “plugged” anything.
Everything surrounding this “theory” is filled with such indefinite phrases.
On your question of monkey's & apes, please note my response #110 to Cowboy Bob's similar question.
As for what role "may have" plays in science, well, science is all about two categories of knowledge -- facts and theories.
The word "fact" means we can observe and measure it, so we know it for sure.
The word "theory" refers to any confirmed explanation of why the facts are what they are.
And science has many theories -- theory of gravity, theory of relativity, quantum theory, theory of evolution, etc., etc.
All are confirmed to work in explaining & predicting future events.
But before scientists ever get to "theory" they must first go through earlier stages like "brainstorming" and "hypothesis".
These words tell us that we are still dealing with speculation and guess-work.
Conversely, when you see a lot of "may have" and "suggests", you know they mean we are dealing with brainstorming & hypotheses.
Nothing wrong with that -- you never get to confirmed theories without first working on hypotheses -- but we need to be clear on what we're dealing with, and words like "may have" tell us.
Does that answer your questions?