In this blog, I discuss the evolution of complex organisms from more primitive ancestors. When I do this, I go way, way, way back in time.. before mammals, dinosaurs, fish, simple sponges, one celled protozoa, and even before the first bacterium! I start with the first replicons. A simple replicon is a single piece of circular DNA like a virus, a plasmid, or a transposon (jumping gene). In today’s world, replicons cannot exist outside of a cell because they lack the machinery required for self replication, i.e. the proteins required for DNA synthesis. However, they may have been able to exist and evolve as parasites within primitive cellular hosts whose genome was composed of RNA that functioned both as hereditary material and as enzymes. The stability of these circular DNA structures may have provided an evolutionary advantage to these primitive hosts, paving the way for the first phase in a process I call hierarchical endosymbiosis. This phenomenon may have allowed life to rapidly evolve through a series of geometric integrations of DNA cassettes in roughly the following sequence of events: virus, bacterium, simple eukaryote, and complex eukaryote. All of these integration events may also be occurring simultaneously.
I present models to explain how these integration events may have occurred at the molecular level, beginning with simple replicons and ending with complex eukaryotic chromosomes. There are also models to explain how transcription is enabled via differentiation and how introns are spliced out of the final mRNA product. These models can be viewed directly at this blog by clicking here or going to the original website that describes them and other processes in considerably more detail.