The “Science” of Partners: Part 2 – Mutual Symbiosis

PART 2: Symbiotic relationships are defined as a relationship between two species where at least one party benefits from the other. Mutualism is a form of symbiosis where both parties benefit from interaction. Today I want to talk about Slowpoke and Shellder so we can understand how Pokémon work so well together.

Slowpoke and Shellder


Slowpoke is a dopey little pink thing that is known for its complete lack of intelligence. All in all, Slowpoke doesn’t do much, preferring to sit around making drawn out, unintelligible noises and occasionally fishing something out of the ocean with its tail (probably by accident).


Shellder is a clam-like Pokémon who hides away between two clam shells, with only its tongue poking out. It can swim in the water in a similar manner to a butterfly but has a bit of trouble with movement on land. However, occasionally a Shellder will clamp on to the end of a Slowpokes tail and, low and behold, a Slowbro evolves!

The great thing about Slowpoke and Shellder is that there is an entire episode of the anime dedicated to understanding the symbiotic relationship between these two Pokémon. In episode 66 “The evolution Solution”, Ash and Co. meet Professor Westwood, who is attempting to understand why Slowpoke evolves into a Slowbro when a Shellder clamps on to its tail. Due to the typical kerfuffle with team rocket, Jesse’s newly caught Shellder clamps onto Prof. Westwood’s Slowpokes tails and they collectively evolve into Slowbro, allowing Slowbro to use on Mega Punch Team Rocket and blast them off again. Prof. realises that the reason the two Pokemon collectively evolve into Slowbro is because both Pokemon benefit from the partnership; Slowpoke is balanced by the weight on its tail and can stand on its hind legs to free its arms, and Shellder gains land mobility. It is clear that these two benefit from each other and are an example of Mutualism.


The funny thing about these two Pokémon is that it is not a true form of evolution (neither in a Pokémon nor a biological sense) because both can revert back to their previous form if the Shellder lets go of Slowpoke/Slowbro’s tail. In a sense, it is a similar sort of evolution as mega-evolution, where the Pokemon temporarily changes form due to a held item. In this case, however, it is not a held item that causes the change, but another Pokémon. The cool thing about this partnership is that they can stay this way perpetually, if they would like.  Another funny thing is that the two are referred to as a single entity, despite having two separate brains and bodies. They also have different forms of evolution in the anime to the game, where in-game evolution occurs with a level 37 slowpoke WITHOUT the presence of a Shellder. Shellder cannot evolve into a Slowbro in-game, despite being necessary in the anime. This is somewhat different to an ordinary symbiotic relationship,  because they can exist quite well without each other, and they aren’t even neccisarily better off with each other. However, they can still enter into a symbiotic relationship none-the-less.

Slowpoke and Shellder evolve

Slowpoke and Shellder also have another side to their relationship. If a Slowpoke is holding or wearing a Kings rock and a Shellder bites onto its head, the two collectively evolve into Slowking. Aside from Shellder now having land mobility and Slowpoke being able to walk on only two legs, Slowking also adds another aspect of their symbiotic relationship. I had to read this a few times, because it seemed ridiculous to me, but it is true to the Pokedex! “When (Slowpokes) head was bitten, toxins entered Slowpoke’s head and unlocked an extraordinary power“(Firered) and “Every time (Slowking) yawns, Shellder injects more poison into it. The poison makes it more intelligent” (Crystal). So the toxin Shellder excretes actually makes Slowking ridiculously intelligent. This benefits the Slowpoke, because intelligence is often quite handy for survival, but it also benefits the Shellder, because being attached to a more intelligent Pokémon may provide extra safety. Now, technically, the secreted substance wouldn’t be toxic to Slowking unless it was harming it also, but it may be toxic to other Pokemon. This could be why Shellder doesn’t clamp on to other Pokemon and make them evolve. If Slowpoke is the only Pokemon that isn’t negatively affected by Shellder’s toxins, it may explain why these two are such good friends.


There are lots of examples of real life organisms that benefit from each other’s secretions (it sounds worse than it is). Many soil microorganisms benefit from nutritious protein and sugar secretions from roots. In one case, the Rhizobium bacterial species use these secretions and, in return, convert nitrogen into a form the plant can use. Like Slowking and Shellder, this is a Mutual symbiotic relationship.

So Slowpoke and Shellder are in a complicated symbiotic relationship, with many different facets and benefits. In the case of Slowbro, the two Pokemon benefit from balance and land mobility, and with Slowking, intelligence and land mobility. However, it is best the two Pokemon stay as one, because “Slowking undertakes research every day in an effort to solve the mysteries of the world. However, this Pokémon apparently forgets everything it has learned if the Shellder on its head comes off.” (ORAS). Yes, if Shellder leaves Slowking, the newly devolved Slowpoke forgets everything it learned. It makes me wonder whether a Shellder stops biting my head the day after exams, because I know that felling all too well.


Disclaimer: I do not own any of the images in this post, nor do


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