Now, gradually over the generations, dig up the pieces and assemble them by how they appear to fit. You get a comprehensible picture, but even though it seems to be the only way to put the pieces together, you can't be certain that you've got it right. Then, wonder of wonders, various techniques of radiometric dating are developed, and when applied to the pieces of the puzzle, the tests confirm that the pieces you've assigned to the early end of the mural do indeed belong there, and so on moving along to the present end. Very nice coincidence. It shows that you're doing it right.
Then, DNA gets discovered, and again you can test your assemply of the puzzle. The individual pieces you've placed next to each other do indeed turn out to be more closely related to one another than they would be to other pieces, thus confirming again, through another independent line of evidence, the manner in which you've assembled the pieces to construct the mural.
The result is the story of life on earth according to the theory of evolution. There is no other way to assemble the picture consistent with the age of the pieces and their genetic relationship with adjacent pieces. But there are gaps in the picture, because not all pieces have been found. Maybe some will never be found.
Notwithstanding the gaps, the picture is visible, and the theory predicts what pieces may exist, and it predicts that if they're found, they'll fit right into the gaps where they belong. Nothing "new" will be found that fits into the "old" end of the mural. Nothing will be found that doesn't genetically relate to the pieces before and after it. Every new piece that gets found is a test of the theory, because it may not fit. Yet each new piece actually does find its proper place in the mural, and the theory survives each new test. Nothing is ever found that contradicts the picture.