We knew that the same genes could be located in different places in different members of the same species. We knew that a lot of DNA was silent. None of these observations led to the prediction of introns. Introns were a complete surprise. The neo-Darwinian paradigm makes very few predictions, yet is constantly being surprised.
Introns are interruptions in the text of eukaryotic genes.
Every time the genome is replicated, they are replicated right along with it. But, for the survival of any creature whose genes carry them, introns are a problem to solve. Somehow, at some stage, introns have to be edited out before the ultimate product of the gene, the protein, can serve its purpose. By 1980 biologists had discovered that eukaryotic cells have an elaborate mechanism for doing the necessary editing. Then, within the cell nucleus, targeted arrays of enzymes and other proteins in complexes called spliceosomes locate the introns, snip them out, and splice the RNA back together.