In fact sometimes these shared errors cannot be shared after all. Like identical typos in essays from students who have never met, sometimes the identical junk DNA could not have originated from a common ancestor even if one believed in the mythical common descent to begin with. In these cases evolutionists agree that lightning did strike twice, such as in this study which found introns at common DNA insertion sites. As one evolutionist put it:
Remarkably, we have found many cases of parallel intron gains at essentially the same sites in independent genotypes. This strongly argues against the common assumption that when two species share introns at the same site, it is always due to inheritance from a common ancestor.
What if common descent had been the only explanation for such similarities in the genomes of different species? That would have been remarkable given the substantial scientific problems with the idea.