Real scientists are never 100% certain about anything (that is the opposite of science, that is called belief or dogma).
The essence of science is uncertainty, a willingness to question any notion and test it, to observe reality and see what it seems to be saying to us.
Having said that, when one has made large sets of observations, one becomes very confident about some things, way over 99.99% confident. Among the things that I have become so confident about are ideas like evolution, chemistry, gravity.
One cannot make any sort of overarching sense of biology without evolution.
And one must always be willing to question, and one needs to exercise some wisdom as to what one chooses to spend one’s time questioning.
And we all need to have things we use in practice to make what sense we can of existence, and we must all start by accepting most of those in a largely uncritical fashion from whatever culture we happen to be born into. So the journey to real science is rarely a comfortable one, as it teaches one to question things that most never question, often leaving very little common ground with the culture of our beginning.