Perhaps the introns found in higher eukaryotes facilitated gene duplication by housing transposable elements. A greater scattering of transposable elements would allow for more rapid shuffling of exons and thereby increasing genome complexity. If transposons pick up an enhancer, it can also affect gene expression if it transposes near a gene. Introns were probably lost during the evolution of rapidly dividing organisms. Much of the human genome contains satellite DNA Satallite DNA represents short repeated sequences with no known function.
Some transposable elements move via an RNA intermediate.
The L1 transposable element carries its own promoter and a gene for reverse transcriptase.