That seems rather implausible given that railroads came about at the same time.

How affordable was railroad travel? Even assuming there was a railroad in the right place, would people have been able to go back and forth often enough for courtship?

Railroads revolutionized cargo. Passenger transport was a cute party trick at first.

Well, there would be a lot more bicycles and they could go a lot more places a lot faster, no? I.E. They would enable a much faster rate of genetic mutation.

No. Bicycles were heavy, uncomfortable products for the first ~40 years of their existence. Rubber tires and pedals didn’t come to bicycles until the 1860s. By that point the US had >30k miles of extensively linking most of the northern states. The modern bicycle didn’t really come into being until the 1890s.

I’m having a hard time getting numbers for track in Europe, but the UK was the real pioneer and Germany followed quickly.

Well, clearly, wherever I heard that from was a terrible source of information! I stand corrected!

Also isn't it a lot more comfortable cross-breeding in a sleeper car than on a bicycle? (Asking for a friend.)