TEAL DEER ALERT. The following is highly speculative and is largely based on my insights and ideas regarding Pokémon biology - as the subject is very near and dear to my heart and I am prone to go a little berserk with my bio-nerdage when I do.
Even in the real world, creatures vary in their regenerative capabilities. Some creatures, such as flatworms, retain blastema (masses of cells capable of growth and regeneration, usually found only in embryonic stages in many creatures) through their entire lives and can famously survive being cut to tiny bits, with each bit regrowing into a complete organism over time. Some invertebrates (such as starfish, octopi and certain arthropods such as arachnids) are capable of growing lost arms so long as their central disc/primary body remains undamaged (sometimes over several moults). Regeneration of limbs or tail segments has been observed in amphibians (most famously salamanders) and certain lizards (although in lizards, this is a different sort of regeneration - the regrown tail is built from cartilage rather than actual regrowth of bony tail vertebrae, and is actually 'designed' to do so structurally - other bits of the lizard don't regenerate like that). Plants may regrow bits of themselves so long as their actual centers of dividing tissue that can grow and regenerate new bits (called meristems) remain intact. As far as regeneration goes, Life is a fairly mixed bag.
Now, Pokémon biology is certainly more robust than anything on this planet. They have fairly impressive cellular regeneration capabilities, especially when exposed to certain triggers that boost it (for example, Pokémon center healing machines, which probably expose them to a certain form of radiation that triggers rapid cellular division and differentiation - or certain moves that trigger the same biological response, such as Recover) which is generally enough to heal wounds to a certain level. Some species would be able to regenerate lost organs, leaves, what have you on their own over time - but I'd imagine that true regeneration of complex structures such as eyes, limbs and the like will be fairly rare - and we'd probably see it in species whose real-world equivalents have similar abilities. That said, I wouldn't be surprised if, say, re-attaching the severed tissue in a medical sort of setting and then running the usual regeneration cycle would have a high success of reintegration of the lost organ, and things such as horns and nails and what have you - derived from a base of living cells that continue growing and dividing over time - can recover on their own even without reattachment. I'm pretty sure that we might have had instances of scars and other 'distinctive marks' formed by injury carried over upon evolution too, in a few forms of canon, but correct me if I'm wrong.
Deoxys, like our starfish here on Earth, can regenerate its body as long as its central core has not been damaged. Unlike our starfish here on Earth, it does it in seconds and looks utterly fabulous while doing it. While its arguable Deoxys' biology is QUITE like that of other Pokémon, it certainly looks more dramatic than an in-game screenshot of 'Recover'
Now, regarding evolution - Katie brought up holometabolous insects (that is, ones that undergo complete metamorphosis - such as butterflies), which actually illustrate the point of what I believe happens during Pokémon evolution.
Looking at a caterpillar you don't see the structures common to adult butterflies and moths - the wings, the antennae, the proboscis (in those species that actually have one) - hell, even the legs. But in all actuality, they are there. The body of the caterpillar contains progenitors for all of these, called "imaginal discs". Before you make any jokes about how it's because you have to imagine they're there - the name actually derives from 'imago', the scientific name for the adult form of holometabolous insects (and incidentally a truly
effing annoying boss in Metroid Zero Mission that is essentially a giant, angry alien bee.)
Which is a holometabolous insect - so annoying AND educational!
Within the pupa stage, many of the larval tissues and structures are 'digested' and dissolved from the inside out (including whatever reserves of food the larva has consumed to fuel its growth). Some structures remain undissolved however - including the imaginal discs I've mentioned and other clusters of undifferentiated cells that form the adult tissues and structures. In at least a number of species, the brain and at least part of the nervous system also remain intact within the "cell soup" that eventually forms the adult, and as a result they can maintain memories and the like from their caterpillar phase. The process is heavily controlled by hormones - and yes, if a caterpillar gets injured but still manages to pupate, these injuries may affect the development of the imago. if imaginal tissues are damaged, the corresponding adult parts may not develop correctly, and should the larva not die midway through the process, the result may be a dysfunctional adult. It's really not a magical process - In a sense, within every caterpillar, there are the building blocks of the adult butterfly, and the metamorphosis process just rearranges the thing to let said adult burst out and wreck everything's shit.
Forget nectar - butterflies sometimes feed on PURE LIQUID SORROW. Or at least, on the salt in reptile tears. Some species also scavenge flesh and there's at least one blood sucking moth. Lepidopterans are hardly the innocuous fluttery things you think they are. They are, in fact, little glorious bastards. Photo by Jeff Cremer.
Of course, insect metamorphosis is not restricted to holometaboly - there are more than a few insects which do not pupate, and rather grow gradually from a nymph form to a full-grown adult over the course of several instars, or stages of development (something called hemimetaboly). Nymphs are usually smaller and their wings are not fully developed - but some species actually have rather different niches as adults to their nymphs - and while you can still see the resemblance, you could probably easily mistake them for different insects. For example - Adult dragonflies and damselflies are aerial superiority hunters with huge damn wings that actually work fairly differently to those of many other insects, whereas their nymphs are wingless, aquatic ambush predators with terrifyingly awesome extendable xenomorph jaws the adults lack. Either way - in both holometabolous and hemimetabolous species - the adult structures are already there, they just need to unfold.
Pokémon, I believe, have something similar going for them. The genetic sequences that, when expressed, lead to an evolved form's phenotype already exist within the creature's genome in the form of structures similar to
operons - sequences of DNA that normally remain unexpressed until conditions necessary for evolution are met. Evolution does not necessarily happen with aging and growth (though it may!) and appears to often be induced through physical conditioning in combat, high emotional states, or exposure to certain forms of radiation and/or ambient particles, and in some places light sensitivities and circadian rhythms may also be involved.
I believe the substances that gradually unlock these regulatory structures in the Pokémon genomes are naturally produced by the Pokémon in response to these assorted stimuli (I personally nickname them
Evodrenalines, as the most common form of which seems to share several commonalities with our adrenaline, although they are not identical in function) - and when they build up enough and activate enough dormant DNA sequences in cells - a rapid cascade of reactions sweeps through the Pokémon, triggering some pretty hyper-accelerated expression, division and differentiation. Areas of cells that are already present but are 'dormant' suddenly stir to life. Body structures change - some grow, some atrophy (including, I'd imagine, glands producing Evodrenalines that are no longer relevant - for example, an Eevee would lose all the rest of its evodrenal glands once evolved into a Vaporeon following a Water-Evodrenal cascade). The process is probably catalyzed by a series of chemicals that coordinate the cascade and bring it to all to culmination (I think of them as also being radiant in nature, emitting the light associated with evolution, and call them
Luminzymes).
The process, apparently, can be stopped if a Pokémon is startled - which could probably be accounted for by an equally rapid reaction that leads to rapid death of new differentiated structures and regeneration of the original sequences, with possible other chemicals (
Antievodrenalines?) putting the process on hold until it is safe to undergo that transformation again. It is probable that the
Everstone stimulates the production of Antievodrenalines at a relatively constant phase - or, if Antievodrenalines are constantly produced at a low rate and the catalyst required for evolution is the equilibrium between Evodrenaline and Antievodrenaline production being broken (and thus, Luminzyme reactions could probably stop the production of Antievodrenalines altogether and the breakdown of ones existing in the system to catalyze the reaction in the rest of the systems?) - stimulates the glands producing them even further to produce more Antievodrenalines than would be feasibly produced by the body naturally.
This is where it gets a bit weird - because this sort of process is bound to be extremely energy intensive and require nutrients and whatever the hell and would take years in real life organisms - whereas in Pokémon it not only occurs in a matter of minutes, but also appears to
PRODUCE energy, rather than consume it! This has been referred to in Gen 4 (where both Professor Rowan and Team Galactic apparently had interest in the energy produced by Pokémon evolution), whereas in the Gen 6 universe this Pokemon bio-energy is alluded to have been once weaponized during the Kalos war via the ultimate weapon, and later collected and converted less explosively and in a more sustainable manner as Devon's patented "Infinity Energy". It is also said to be the energy behind Mega Stones. All of the above cannot be explained through any sort of conventional biology - but presumably correlate with the nature of Pokémon as 'magical creatures' as opposed to complete 100% biological organisms, attuned with and capable of tapping into some form of elemental energy planes and what have you. It's probable that energy is harnessed from whatever exodimensional physics-breaking source it has to catalyze the more physics-breaking aspects of evolution. As for Mega Evolution - probably involves sequences that are particularly expensive to express and may be crippling to carry around (y'know, like the big heavy structures some species put on during mating seasons, but more pointy) and therefore, are only used when a creature is supercharged with that form of energy (which clearly also boosts their combat capabilities), and once not needed, the end results of the evolution are simply shed and/or absorbed back in an evolution-cancellation sort of way into the regular more energetically favorable conformation, or something.
Either that or we call it what it is - Digivolving Goddamn Pokémon.
Anyhow. I've gone on this entire long-ass ramble for long enough so I'll get to the point. Yes, Evolution leads to a lot of change and growth and may cause strange and wonderful things, but basically, if your arm is supposed to elongate and grow fins when you evolve, but your arm isn't attached when you evolve, there will be nothing to elongate and grow fins OUT of. If you're missing an eye and you don't have the basic blueprint for an additional eye when you evolve, there'd be nothing to grow into it. Unless you're one of the few species that are simple or modular enough, or possess enough undifferentiated clusters, Evolution most likely won't de-cripple you. By the same account, if you evolve into something with multiple arms and whatever bit of you that grows the arm is seriously injured, you're most likely going to grow a stunted arm, if at all - assuming you even survive in the wild, because let's not forget that unlike in the sanitized, "kiddified" world of the games and the anime, in a real world type setting Pokémon don't just prey on each other in Pokédex entries and offscreen. Pokémon are very adaptable, robust and supplemented by a great deal of elemental fuckery - but quite a few individuals will be grievously injured in battle, or won't get enough nutrients, and thus have a much lower chance of survival in nature, where access to human-derived medical care for Pokémon isn't all over the place. The evolutionary arms race marches on.
So basically that I said here chalks down to this: It really depends on the Pokémon species, its overall health and the airspeed velocity of an unladen Hoenn-born Swellow.
Teal Deer, return!
