This is a good conversation starter on how neutral evolution alone can build complexity.
See this from Doolittle:
As we pointed out previously, machines of marvelous complexity such as lightharvesting antennae in photosynthesis, RNA and DNA polymerases and their attending initiation, elongation, and termination complexes, apparatuses for import, folding, and degradation of proteins, or the cytoskeleton and its motors, all might have grown to their current form through a process of CNE accretion. The same argument could apply to large and complex regulatory networks, which are often described as being ‘‘ﬁnely tuned’’ but might be better interpreted as ‘‘runaway bureaucracy’’ or biological Rube Goldberg machines where what could be a relatively simple task is performed though many steps by an unnecessarily complex machine.
See this @colewd (but don’t recycle any arguments please), from Moran:
For example, there is good reason to think that the evolution of the complex spliceosome that removes introns has evolved by mainly non-adaptive evolution.