"Pigeons. It's amazing how adaptable they are - and are yet one species..."
Um no, there are many many species of pigeons. Try again.
Indeed you're right. The pigeon family encompasses many species, all over the world. So much for that argument, eh?
A guy can see photos of lots of different pigeon species at the link below:
http://www.camacdonald.com/birding/Sampler3-PigeonsDoves.htm