Almost by definition, increases in biological complexity, whether at the molecular or cellular levels, or even at the level of species diversity, imply an increase in the effective information content of DNA in the system as a whole. An important question, which goes to the heart of the concept of biological complexity, is to ask to what extent any diversity-associated increases in information content are essentially discrete or are part of a continuum in which the evolution of complex biological systems is linked to incremental accretions of DNA information.