>>9719698Simply put, Tamagotchi doesn't really do the whole "linear character evolution" thing that Pokemon and some other "mon"-franchises do. Your quality of care influences its personality, which in turn effects its evolution. The design principle for the original cast of characters (on the P1 and P2) was that you could A) see a clear and definitive growth pattern from baby to adulthood, and B) you could easily tell if you did well or did poorly based on how cute or ugly the end result was. And they had to do it with 16x16 sprites on a 32x16 black and white LCD, which is why the designs are so simple compared to more modern characters.
