Speccer
An individual who likes or practices the art of speculative evolution or speculative biology, which can include future evolution, the future of humanity, alternate evolutionary timelines, speculative paleontology/paleobiology, the evolution of life on another world, or the evolution of life on a planet that has been seeded with terrestrial organisms.
"I know it looks too much like a rabbit but its supposed to be a dog!" - something only a speccer can say. Or a kindergartner in art class.