Question: How did new biochemical pathways, which involve multiple enzymes working together in sequence, originate?

Kevin Healy answered on 15 Nov 2014:

Complex biochemical pathways would have started off as a few molecules interacting in a simple manner. Mutations in genes usually mean the pathway breaks down and so the individual dies and cant pass on the new mutated gene. However mutations can cause things like dublications were the same gene is coded twice by accident. If this is a gene that codes for the molecules in a pathway and if a mutation now affects one of the genes the other gene can act as back up making sure the biochemical pathway doesnt break down and the individual can pass on the new dublicated gene. This is important as now you can have a functioning biochemical pathway but now while one of the genes carries out the pathway the other gene is free to become mutated.
If it so happens that a mutation causes that dublicated gene to produce a molecule that makes the pathway work better or faster (for example by mis coding a section of a gene an enzyme shape can be changed which can change how it interacts with other molecules) then you have a new more complex pathway with three parts to it instead of two. This can go on and on over evolutionary time (millions of years) until you have pathways that look unfeasably complex.