What if the particles you were made of were much smarter than yourself as a whole? You'd feel pretty annoyed, wouldn't you? Well, such is the case with Pokemon. A Pokemon's cells are much more complex than those of humans. Pokemon cells can turn themselves into much more complex cells than simply "Skin cells", or "brain cells". If a Pokemon was manipulated genetically in a certain way (of which will be explained later), you could very well turn those cells into cells composed of Steel elements. Or it could make itself out of Potassium (though it wouldn't be very practical). A Pokemon's cells can use the atoms around it, and "trade" it's own atoms with those.Humans have exploited the nature of said cells for their own use in Pokemon battling.
Steelix is a perfect example. By attaching a steel coat onto an Onix, it changes into a Steelix through trade. When a Pokemon is sent through a trading machine, it has its atoms and molecules seperated. When it arrives in the hands of another trainer, the Pokemon tries to grab any excess Atoms that flew off in the trade. By doing this, it may either grab the atoms from its trade item, or simply grab atoms from "nowhere". Why the latter occurs is still unknown to scientists around the world. However, for Pokemon cells to partake in such atom trades, it must meet certain standards. Standards vary from Pokemon to Pokemon. Some Pokemon have been known to be forced to change due to toxins. Few Pokemon only make use of their special cellular abilities when in a tolerable mental state. Most evolve through these two criteria: Radiation, and battle.
Battle is a tricky one. Pokemon battle each other in the wild for food - for example, Shuckle shells contain some particularly tasty juices, craved by many a Pokemon. Each time a Pokemon fights, Chemicals are secreted by the brain is pumped around it's body. By releasing these chemicals from the brain area, the mood of the creature alters dramatically, readying it for further battle. Once a Pokemon is done fighting, these juices flow back to the brain - but leave some remains in the other parts of the body. These chemicals are used by the cells as food, to make it stronger. Different amounts of said chemicals are released depending on its opponent, and it's growth is altered because of this. When a Pokemons cells are overloaded with energy from the chemicals, it will either experience what is known as a growth spurt, or take on an entirely new form.
Radiation is a recently discovered one, but is quite simple. When a Pokemon is exposed to Radio waves, the radio waves garble the cells ideas of when to evolve, creating "forced evolution". If a Pokemon is given one of the many elemental rocks, the rock will provide energy for said evolution, along with radiation. However, some Pokemon are truly forced through evolution through unnatural Radio Waves. The Pokemon lacks the Energy to evolve by such means, and is exausted and weak afterwards. A Pokemon may also not evolve properly without real means of energy. It may be discoloured, have disfigured limbs, or lack the strength that the evolution should inherit.
