The fallacy of this is that you've made an unfounded assumption that this is an either/or problem -- that intelligent intervention and natural processes are mutually exclusive possibilities. However, we already know for an absolute fact that they are NOT mutually exclusive possibilities.
If there's no data to show that interventions occurred, then, by Occam's Razor, it makes sense for scientists to assume that it didn't.
Given that we have practical experience in doing intelligent intervention, it makes an equal amount of sense to assume that it did occur. Indeed, given our human propensity for doing design, Occam's Razor might in fact suggest that design is the better assumption.
The fact that scientists nevertheless invariably assume "no intervention" is evidence of their underlying materialist assumptions.
If there were to be found observational data that showed that intelligent interventions were necessary, then honest scientists would have to accept this idea.
There's an underlying bias there, too, about what constitutes acceptable evidence for design. Based on the way that humans practice intelligent intervention (or design of almost any sort), the proper context for a discussion of design is not "necessary," but rather "desired results." Moreover, there are often a variety of ways to achieve desired results, so "necessity" is not determinative of how a design might turn out -- we would therefore not even expect to find a design to be full of "necessities."
I acknowledge the difficulties inherent in detecting "desired results," but it does not invalidate the underlying truth that they are the driving force behind the process of design. It's worth noting, though, that the "nature's ingenious adaptation" explanation, tacitly relies on "desired results," rather than any argument from necessity.
I am not arguing natural process vs. intelligent intervention as an either/or proposition. I am arguing natural processes without intelligent intervention vs. natural processes with intelligent intervention as an either/or proposition (which it must be via the law of excluded middle.) When I refer to intelligent intervention being necessary, I mean necessary to explain observation, not necessary for life to develop as it has. It is entirely possible that life could develop by natural processes alone, but in actuality it had help from intelligent intervention. For science to accept this, there must be evidence that intelligent intervention did indeed occur. Occam's razor certainly points to the assumption that intelligent intervention did not occur. There is no scientific evidence showing that any other intelligence other than human intelligence exists or has existed in the past. (Not saying it hasn't, absence of evidence is not evidence of absence. But in the absence of evidence, science will assume that there hasn't been) Since intelligent intervention in the development of pre-human life would require a non-human intelligence and there's no evidence that any such intelligence exists (or did exist in the past), Occam's razor points to the simplest explanation, namely that the development of life occurred via natural processes without the help of any intelligence. As I have stated before, if evidence is presented that shows the likely existence of such a non-human intelligence, science should (and I believe) will take it seriously. If the evidence points to the likelihood that such an intelligence interfered with the development of pre-human life on earth, then again, I think science should take this seriously. (I have my doubts about some scientists doing so, but that's a flaw in the nature of these scientists, not in the current theory of evolution.)