Digimon hatch from types of eggs which are called Digi-Eggs (デジタマ, Dejitama?). In the English iterations of the franchise there is another type of Digi-Egg that can be used to digivolve, or transform, Digimon. This second type of Digi-Egg is called a Digimental (デジメンタル, Dejimentaru?) in Japanese. (This type of Digi-Egg was also featured as a major object throughout season 2 as a way of Digivolution available only to certain characters at certain points throughout the season.) They age via a process called "Digivolution" which changes their appearance and increases their powers. The effect of Digivolution, however, is not permanent in the partner Digimon of the main characters in the anime, and Digimon who have digivolved will most of the time revert to their previous form after a battle or if they are too weak to continue. Some Digimon act feral. Most, however, are capable of intelligence and human speech. They are able to digivolve by the use of Digivices that their human partners have. In some cases, as in the first series, the DigiDestined (known as the 'Chosen Children' in the original Japanese) had to find some special items such as crests and tags so the Digimon could digivolve into further stages of evolution known as Ultimate and Mega in the dub.

Answer this question, if possible (if impossible, reply "unanswerable"): What effect does digivolution have on digimon?
changes their appearance and increases their powers