Here I have a Genjintchi Cave Man tamagotchi. Just for the record I have another that I am selling right now. He is $40 and is new, never used. He was taken out of the package to remove the batteries to preserver him.
This tamagotchi is very cute. He evolves according the the theory of evolution and can even regress if you do not take care of him correctly. Right now he is in his tadpole looking stage. He makes pottery and I reward him. If raised correctly he can grow into the caveman. Otherwise he will look like some kind of homo erectus or mammoth.
Others say that this tamagotchi is boring but I find it fascinating because it is the only one that ACTUALLY evolves! =)