Why should we expect there to be any mathematical foundation to this stuff? It's quite possible to imagine an alternate universe where GAs and neural nets don't work. Because they have different datasets that don't fit the structure of NNs well. Or problems that happen to not be solvable by the search strategies of GAs.
In fact we have many such problems in our own universe. I can give many examples of things NNs and GAs don't work well on right now. Those are just ignored by the research.
In fact we have many such problems in our own universe. I can give many examples of things NNs and GAs don't work well on right now. Those are just ignored by the research.