The Secret of Evolution is a key plot element in Dragon Quest IV. It is said to be integral to the development of all life everywhere, but extremely dangerous if it falls into the wrong hands.
The Secret of Evolution was originally discovered by Estark, Lord of the Underworld, a thousand years before the game begins. Estark used the Secret of Evolution to transform his body and become the ultimate life-form, and in doing so, became the most powerful being on the planet. However, despite his power, he was still able to be sealed away by the efforts of the Zenith Dragon within a tomb deep beneath Mamon.
After this, the secret was lost until it was rediscovered by the alchemist Mahabala, father of Maya and Meena. Unfortunately, his apprentice Balzack murdered him and stole his research, using the imperfect version to empower himself and Marquis de Léon. He passed the secret onto their master, Psaro, the Master of Monsters. Psaro had held off on using it himself for fear of losing his sanity. However, this changed when Aamon had his lover Rose murdered by humans, causing him to fly into a rage and utilize the Secret, taking on a form very similar to that of the transformed Estark.
Unbeknownst to either Psaro or the Chosen Hero, Aamon had expected them to kill each other in Nadiria while he perfected the Secret of Evolution and assumed dominion over all monsterkind. This plan was subverted when the Chosen was able to resurrect Rose using the Yggdrasil flower and save Psaro from his madness. Afterwards, the Hero, Psaro, and party confronted Aamon in his ultimate form and and destroyed him, eliminating the Secret of Evolution with him.
In the Nintendo DS remake of Dragon Quest V, it was said that Grandmaster Nimzo was an evil human who took the secret of evolution to become a god. However, he ended up being sealed up, just like Estark.
The secret of evolution is mentioned by a scholar in Coburg Castle who claims he is studying psarology, the name of the science being derived from the legend of Psaro.
Usage and Effects
The exact steps one must take to perform the Secret are unknown, but it can be assumed that it makes use of magic or is even a form thereof. The technique acts to physically alter a person's physical characteristics, generally making them larger and stronger, and often adding other bonuses as well. For instance, Estark and Psaro both acquire an armoured carapace. This culminated with the final forms of both Psaro and Aamon, who became a bizarre, towering entity with not only a face on the abdomen, but a second head with three eyes.
For some reason, the Secret of Evolution requires the Armlet of Transmutation in order to work as intended. If attempted without it, the results are imperfect and often unpredictable. Marquis de Léon, fittingly enough, became a monstrous lioner, while Balzack became a huge and bloated lizardman. Each of these forms has a weapon unique to it - Estark and Psaro use two swords, the Marquis uses bared claws, and Balzack used a club - but whether this is an effect of the transformation or simply a matter of personal preference and common sense is unknown. Since Grandmaster Nimzo took on a form powerful enough in its own right with no mention or indication of him having access to the Armlet of Transmutation, there may be alternate ways of using the Secret of Evolution other than the Armlet and still achieving equally successful results.
One major side effect of using the Secret of Evolution is loss of one's memory. Neither Estark nor Psaro have any recollection of their past after using the Secret other than their own names. This side effect only takes place if the Armlet of Transmutation is utilized to achieve the full potential of the Secret of Evolution, as neither Balzack nor Marquis de Léon experienced memory loss after performing the Secret imperfectly. Interestingly, Aamon still has his memory intact after using the Secret. This may indicate that he knew of a way to bypass the side effect of memory loss, a method that neither Psaro nor Estark were aware of.
In the remake, Rose's tears were able to reverse the effects of the Secret of Evolution on Psaro, perhaps due to her heritage, her own unique magical traits, or her love for him. There may be other circumstances necessary in order to make this reversal possible as well.
It seems some demons in the Dragon Quest series, such as Mortamor and Orgodemir, can naturally transform without need of the Secret of Evolution. In Dragon Quest X, the transformation of Nelgel was a result of him being exposed to the true darkness at the top of the Heart of Hell.