What if you lose the race for the Theory of Evolution? There's no need to quit, you can still win! Against the AI you'll just have to figure out which techs you're behind, and work doubly hard diplomatically to reach tech parity. This is nothing new, as it resembles the tech race in the Ancient Age. If you think you've got a good shot at Hoover Dam, definitely go for it (it's too perfect a Wonder for the AI), otherwise stick to the upper branch and start kicking some butt with Transports loaded with Infantry, Artillery and Workers, guarded by Destroyers and what-not.
If you lose the ToE in an MP game...well, I've never been in that situation, so no comment. I would probably form a coalition against the one who did get it...he or she still only has Infantry and Artillery to fight with until Tanks!
The Industrial Age is an exciting age, even though there's more or less a best way to tackle it. Against the AI, it truly feels like you're playing a different game: while you're optimizing your nation with Railroads and Factories and building up zounds of Infantry and Artillery, the AI is using Draft to get Riflemen and is entering Communism. Above all, the AI is not putting nearly as much emphasis on the Theory of Evolution as you are. Truly, if there's a time to cheese out the AI and pull ahead, it's in the Industrial Age. Against human opponents...beware!
Final recap: Here's my suggested tech queue for the Industrial age (optional techs obtained via trades):
All comments welcome; thanks for reading!