The Pokemon Evolution Theories is a page dedicated to minor theories about the origin of certain Pokemon, the evolutionary chains of certain Pokemon, and miscellaneous guesses on connections between two Pokemon species. None of these theories should really be big enough to warrant a whole page. If a theory gets too big, it should be put into a new page and the link to it should be place in this section, underneath its own title.
Aerodactyl Evolved into Zubats
Aerodactyl have gone extinct in the Pokemon world. This theory states that they evolved in the Bat Pokemon, Zubat. Upon initial inspection, their body, wingspan, and the style of the wings are very similar. Aerodactyl's shiny version has a closer color scheme to Crobat, Zubat's next evolutionary stage, as well. Crobat only possesses teeth on its lower jaw and Aerodactyl's lower jaw is built heavily, with only a break and no teeth visible for the upper jaw. Aerodactyl knows Supersonic, Bite and Wing attacks for its starting moves, and Zubat quickly learns these as its initial level-up moves.
The "plant" on Bulbasaur's back is really an Oddish growing symbiotically with what would otherwise be a fleshy, defenseless baby frog. The Oddish gets more nutrients than it would get sulking around at night. Oddish feet are supposedly its roots, and it can learn ingrain, and then do so into the skeleton and nervous system of the Bulbasaur. Female Venusaur's are pictured to have a seedling in them, possibly suggesting they are always "fertile" and producing seeds. If a male Venusaur is around, a Bulbasaur will be born! If not, the seed will germinate into an Oddish.
Butterfree and Venomoth's Sprites Were Switched
When Butterfree and Venomoth's evolutionary chains are put next to each other, some people may say that Butterfree and Venomoth look like they should switch places. Both of these Pokemon's sprites are much better suited for the other one's chain.
Cubones Wear the Remains of Their Mother
When a mother Kangaskhan dies, it leaves its Kangaskhan cub on its own. The Kangaskhan cub uses the skull and a bone from its mother to use as protection and becomes a Cubone. Then through malnutrition or adapting to a different lifestyle, the Cubone evolves into a Marowak. Female Marowak's later evolve into Kangaskhans, and the cycle starts all over. This is self evident, as Cubone appears rather similar to the baby Kangaskhan that rides around in its mother's pouch. Also, 'Bonemerang' (Cubone's signature move) refers to boomerang just as 'Kangaskhan' refers to Kangaroo. Kangaroo and boomerangs are both natively Australian themes. Before Pokemon Red/Blue released, the developers decided that Kangaskhan needed to be separated from the previous two stages to become its own standalone Pokemon. The reason for this is that, being a kids game, it wouldn't do to allow small children to learn that a Cubone is actually an orphaned baby Kangaskhan wearing its dead mother's skull on its head and slinging its bones around like clubs and boomerangs. However, the team didn't have time to delete the code at the last minute. Instead of deleting the code, they simply wrote a new non-evolving Marowak and moved the old one to an empty slot... with no number. This catchable Pokemon is M', Missingno's sister. M' is actually a scrapped prototype of Marowak. This theory can be confirmed if you catch a M' and level it up, it evolves into a Kangaskhan.
Gengar is Clefable's Shadow
Through beta artwork, Clefable and Gengar have been confirmed to one of the earliest designed Pokemon. Clefairy, Clefable's preceding evolutionary stage, was originally going to be the mascot of the series, instead of Pikachu. It was going to be a pretty important Pokemon to say the least. Gengar is known as the "Shadow Pokemon", but the shadow of what?
Well, take a look at a picture of Clefable, then of Gengar. Their body shapes are almost exactly alike, with the only real difference being that Clefable has a swirly hair, while Gengar has spikey hair. Now, look at their typings -- Clefable is a "normal" type while Gengar is a "ghost" type. Due to both of their immunities, neither of them can hit each other with STAB attacks, since they'd be immune to each other. You ever tried to hit your shadow? Additionally, Gengar is named after a doppelganger, the ghostly double of a person.
Parasect is Controlled by Its Mushroom
Parasect's growth has been stunted by the mushroom that has resided on its back since birth. The mushrooms sink their spores into the host's brain, giving the parasitic mushroom total control over the Paras. Due to being possessed for so long, the eyes have whited out and the mushroom has drained almost all of the Parasect's life force, which gives the mushrooms the energy to grow into a gross exaggeration of its former size. Once they are that huge, they take total control of the Parasect's mind, creating a "hivemind" with other host Parasects. To ensure survival, the mushrooms force the Parasect to breed and once the eggs are laid, the mushrooms coat the eggs with their parasitic spores, ensuring their offspring will wind up in the same, dead-eyed and doomed fate they currently have.