"Never say 'higher' or 'lower'."  --the notebooks of Charles Darwin

 

The evidence, limited as it is, is the other way: that prokaryotic organisms *lost* introns in an attempt to optimize their genomes.  The chloroplasts in plants, which are believed to be the descendants of cyanobacteria that were encapsulated long ago, have introns, which suggests that the common ancestor of all prokaryotes did too.

It's a mistake to think that evolution proceeds inexorably from simple to complex.  Evolution is adaptation to local concerns, and has only local directionality.