I don&#x27;t agree that people have long thought these were linear pathways.  My undergraduate education was more than 20 years ago and beyond having the &quot;Biochemical Reaction Pathways&quot; chart on my wall (<a href="http:&#x2F;&#x2F;web.expasy.org&#x2F;pathways&#x2F;" rel="nofollow">http:&#x2F;&#x2F;web.expasy.org&#x2F;pathways&#x2F;</a> has been around 40 years) which clearly shows things as a graph structure, it was commonly taught that there were complex networks, regulated at many points.