I am not claiming that scientific knowledge is fixed and immutable. There is nothing fixed and immutable about evolutionary theory and that is well worth celebrating. But trying to compare what I'm saying with phlogiston theory is plain daft. The scientists of the day were guessing. They had no body of evidence for the existence of a substance called phlogiston. Speculation is not evidence and their reasoning went way beyond what was justified by their observations. In the case of evolution there is an overwhelmingly-huge body of good, solid, reproducible evidence that it occurs. It is not going beyond the bounds to say that the fact of evolution is incontrovertible. Not the details or the mechanisms or even some of the evidence, but the notion, the idea, the concept in its general thrust. You are never going to see that overturned. That evolution happens is not "a consensus of opinion." Like my fig tree, it's true. It's there. Like my fig tree, there's still plenty to work on. But....evolution, in its general thrust, is true!