When I was doing my PhD research, in the middle of the last century, the nature and complexity of the RNA transcripts of the genome was a topic of lively debate, into which my own work became drawn. The complexity of the mRNA population in a given tissue, cell‐type or developmental stage—considered as transcripts that were polyadenylated and associated with ribosomes—was estimated to represent some 40–50,000 distinct mRNAs of typical size, both in plants and vertebrates. The advent of high‐throughput sequencing has pretty much confirmed these numbers, although they are derived from fewer genes because of alternative splicing, and variable sites of transcription initiation or polyadenylation. It was already clear back then that the mRNA populations of different cell types were overlapping but not identical, providing a key plank in support of the idea that an invariant genome could specify different developmental fates via the synthesis of varying subsets of proteins encoded by that genome [1]. As soon as introns were discovered, we also had a clear—if retrospectively only partial—explanation …