Read this: Interspersed repeats mainly come from transposable elements (TEs), but they also include some protein coding gene families and pseudogenes. Transposable elements are able to integrate into the genome at another site within the cell. It is believed that TEs are an important driving force on genome evolution of higher eukaryotes. TEs can be classified into two categories, Class 1 (retrotransposons) and Class 2 (DNA transposons).
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What do researchers think transposable elements are key factors in when considering higher eukaryotes?
genome evolution