Were introns “early” or “late”?
If introns could be dispensed with in bacteria, then perhaps they had no function. Alternatively, whatever function introns had, either was not necessary in bacteria, or might be achieved in other ways by bacteria. Since members of many bacterial species appeared to be under intense pressure to streamline their genomes to facilitate rapid replication, if it were possible they would have dispensed with any preexisting introns and/or would have been reluctant to acquire them. On the other hand, if introns played a role and/or did not present too great a selective burden, eukaryotes would have tended to retain preexisting introns, or could have acquired them (Raible et al. 2005). Knowing the function of introns seemed critical for sorting out these issues. There were many ingenious suggestions. Some thought introns were just another example of the apparently non-utile “junk” DNA which littered the DNA of many eukaryotes. However, some principles to guide investigation of a possible error-
