New non-coding RNA genes evolve from junk DNA

What if we told you that you have a brain not because of natural selection, but in spite of it?

In the latest issue of Cell, Professor Alex Palazzo and his collaborator, Eugene Koonin from the NIH, have advanced a new theory on how biological complexity evolves. Most scientists assume that novel genes evolve as a direct consequence of natural selection, but Palazzo and Koonin present evidence that a different process, called Constructive Neutral Evolution, or CNE for short, is likely responsible for the generation of novel non-coding RNA genes. Moreover this process requires an overabundance of junk DNA that is transcribed into junk RNA.

Two important key concepts that underpin this argument are 1) that organisms that are subjected to high levels of natural selection tend to eliminate all of the raw materials, in this case junk DNA, that are needed for the evolution of new non-coding RNA genes; and 2) when novel genes do arise, they typically contain some biochemical activity, or “excess capacity”, that is created by neutral mutations and serves no immediate purpose. Typically this excess activity would be eliminated by natural selection, however since multicellular organisms are subjected to weak selection pressures, this extra superfluous activity sticks around for enough time that it allows other functional units to decay by absorbing debilitating mutations. Eventually these functional units require the novel components and as a result the overall system becomes more complex. This process may underpin the complexification seen in multicellular organisms.