> I don't believe that just because you say so.
Good! Skepticism! Display similar skepticism in claims in ancient texts, and you'll be on your way.
> if someone doesn't fully understand the theory, how can he be so certain of its veracity?
Do you understand the tensor calculus required for a good understanding of the Theory of Relativity? No? Would you be willing to stand next to an H-Bomb, then? Do you understand the math behind quantum gravity? No? Then would you be comfortable standing under a suspended 16-ton weight?
Heck, I make rockets, and I don't have a deep understanding of the relevant combustion phenomena. I routinely cast urethane resin parts from silicone rubber molds built off of Bondo originals... all of which use chemical reactions I don't know squat about. Yet I am substantially certain that if you mix A and B together, you get a solid with reliable properties.
Similarly, one doesn't need to understand the complexities of mutations and continental drift and sediments turning into rocks to look at the fossil record and notice that critters change over time.
If I may use an analogy. Darwin is to Evolution what Newton was to gravity. Now Newton was pretty smart and his theory and equations work for most every day life. However, they fall apart at relativistic speeds. Now along comes the gravity equivalent of a creationist, who says that because Newtons work doesnt work at speeds approaching c that therefore the whole theory of gravity is wrong, and proves the existence of God. That is what ID and creationist proponents are putting out there. Taken out of the context of evolution, does the above sound logical at all? Gravity is still gravity. Now what evolution needs is its equivalent of Einstein to come along and revise and true up the theory so that it works in almost all cases. However, Newtons stuff being simpler, and easier to understand is still taught in the schools. Same thing here, Darwins theory may not work in all cases, but overall it does work for everyday use. Just because you dont understand relativity, doesnt mean you cant discuss laws of motion.