The genomes of complex multicellular organisms on Earth are characterized by high intron-richness

The origin and evolution of complex multicellularity (CM) on Earth is of particular interest for Astrobiology to search for complex alien life elsewhere in the universe. However, CM is restricted in our planet to eukaryotes and has evolved independently a few times within red and brown algae, plants, animals, and fungi. Paradoxically, the complexity of eukaryotes does not correlate with genome size or the total number of genes, but it seems to correlate with the expansion of DNA that does not encode for proteins (ncDNA), such as spliceosomal introns and regulatory non-coding RNAs. Here, we present a formal definition for CM and summarize some findings showing that the genomes of CM organisms and their closest ancestral relatives are indeed characterized by high intron-richness, regardless their genome size. These findings support our hypothesize that CM on Earth is the outcome of major evolutionary transitions involving, among other factors, the presence of innovatory changes in genome structure and cell diffeentiation due to the convergent evolution of specific ncDNA classes.