text: This work also explains why genomes such as the human genome have billions of bases, and why only a small fraction (~2%) codes for proteins and other regulatory elements. If split genes originated from random primordial DNA sequences, they would contain a significant amount of DNA that represented by introns. Furthermore, a genome assembled from random DNA containing split genes would also include intergenic random DNA. Thus, genomes that originated from random DNA sequences had to be large, regardless of the complexity of the organism.
  The observation that several organisms such as the onion (~16 billion bases) and salamander (~32 billion bases) have much larger genomes than humans (~3 billion bases) while the organisms are no more complex than humans comports with the theory. Furthermore, the fact that  several organisms with smaller genomes have a similar number of genes as human, such as C. elegans (genome size ~100 million bases, ~19,000 genes) and Arabidopsis thaliana (genome size ~125 million bases, ~25,000 genes), supports the theory. The theory predicts that the introns in the split genes in these genomes could be the “reduced” (or deleted) form compared to larger genes with long introns, thus leading to reduced genomes. In fact, researchers have recently proposed that these smaller genomes are actually reduced genomes.