With respect to scientific thinking, it is common for a belief to be predicated on Plato's epistemic rule for what constitutes knowledge. (i.e. Justified True Belief.)
Is your belief true, and are you justified in believing that this thing is, in fact, true?
According to Plato's dialogues, one cannot have knowledge of something unless they believe in this something, and if this something can be proved to be the case.* It is the word proved, in this context, that typically matters most to scientists and critical thinkers.
*This presupposition ignores the Gettier problem, in epistemology, which purports to disprove Plato's JTB concept of knowledge. However, interesting as it might be to go down that rabbit hole, I must insist that we temporarily accept this presupposition, for the sake of argument.
Proof requires evidence.
Evidence is - or, should be - the only thing that matters in science. The premise of empirical knowledge is that, once all the data is collected, analyzed and interpreted, beliefs will tend to shift in accordance with what the agreed upon result of this scientific synthesis seems to be, at least transiently.
The reality, however, is that, with particular regard to biological research, there is so much noise in the system, so much data to collect in different ways, so many hypotheses to refute as it were, that just about anything could have some credence. All one has to do is spin the data a certain way, give it a certain flare and a plausible underlying mechanism, and BAM!, we have a potential belief-winner.
If biology were more like analytical chemistry or experimental physics, it might be a different story. More solid evidence would be required to confirm mechanistic principles that underlie various conjectures. Experimental conditions set to confirm or disprove a cause and effect relationship would hopefully elucidate "the answer." And if, in 20, 50 or 800 years, someone has falsified the previous result with a more refined experiment and observation, the beliefs change accordingly.
A great example of such an event is the shift that took us from Newtonian (classical) mechanics to relativistic mechanics to describe so-called large scale, cosmological occurrences. It is understood to be the case in the physics community that Isaac Newton had it right with his laws of motion, but, when Albert Einstein came along and ruined all that perfect mathematical deliciousness with his theories of special and general relativity, an amazing shift occurred (over time) where people began to realize that he was, in fact, indisputably correct - with the implicit understanding, of course, that his theories were also subject to falsification, as are all other theories -- and their beliefs about Nature changed to reflect this paradigm shift.
The trouble is, biology -- although it rests on the laurels of physics and chemistry, from a purely reductionist perspective -- functions quite differently from its sister sciences, wherein, due to the innumerable and often immeasurable variability in the systems, it can be nearly impossible to discover "the answer." And, in fact, it may be the case that there is no such thing as the answer, at all; there may indeed be more than one answer, more than one mechanism that causes the exact same outcome or set of results.
Because of the aforementioned complexity in studying the life sciences, and the nature of biological phenomena to be convoluted and elusive, it is easy to suspect that we have an answer to a particular question, when, in fact, we might well be dead wrong. Or perhaps we're not so wrong, but just a little wrong. Or maybe we're on the right track, yet still no cigar. Or maybe we are right, but our ideas behind the mechanism are too simplistic....
Ultimately, my point is simple: At the end of the day, everyone's hypotheses are valid - much more so, of course, if they are predicated on previously "proven" theories. More importantly, it is that science is an ever-changing, constantly adapting discipline, which requires supple minds to morph along with it. You cannot be a rigid thinker and call yourself a scientist. It is inappropriate for the discipline, and, if you are a biological researcher, it will (at least in my opinion) turn out to be the bane of your existence. You ought not conduct your life as a scientist by trying to angrily refute every conjecture thrown your way, regardless of your purported expertise or your credentials, even if you assume to "know" that they are incorrect. It is a fruitless endeavor.
The truth will out, in the end. As it did with Newton and Einstein, and then again with Bohr, Heisenberg and the advent of quantum mechanics, the data will eventually shine a light on the nature of reality, as we're meant to understand it, when the time comes. In the meantime, please do not assume I am suggesting you take the superficial view that these last few paragraphs appear to be saying, "every conjecture is okay, because it could be right, or it could be wrong, and you may just note know yet," or something like that. Rather, I'm saying, "Don't fret over every little thing, or take yourself (or others) too seriously."
"It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle