From wikipedia
Biological functions and evolution
As a first approximation, it is possible to view introns as unimportant sequences whose only function is to be removed from an unspliced precursor RNA in order to generate the functional mRNA, rRNA or tRNA product. However, it is now well-established that some introns themselves encode specific proteins or can be further processed after splicing to generate
noncoding RNA molecules.
[18] Alternative splicing is widely used to generate multiple proteins from a single gene. Furthermore, some introns represent
mobile genetic elements and may be regarded as examples of
selfish DNA.
[19]
The biological origins of introns are obscure. After the initial discovery of introns in protein-coding genes of the eukaryotic nucleus, there was significant debate as to whether introns in modern-day organisms were inherited from a common ancient ancestor (termed the introns-early hypothesis), or whether they appeared in genes rather recently in the evolutionary process (termed the introns-late hypothesis). Another theory is that the
spliceosome and the intron-exon structure of genes is a relic of the
RNA world (the introns-first hypothesis).
[20] There is still considerable debate about the extent to which of these hypotheses is most correct. The popular consensus at the moment is that introns arose within the eukaryote lineage as selfish elements[
citation needed].
Take home points:
Intron can code for other non coding protein. Help with splicing = more biodiversity. In term of evolution, maybe it was code for something in the past but now it's non function (theory).
