The Mascotian Effect is the name of the phenomenon that causes those living in Mascotia to adopt anthropomorphic traits, and appear somewhat neotenous. These effects are thought to be by-products of the life-prolonging effect the dimension containing Mascotia has on creatures.
If a Mascotian leaves the dimension surrounding Mascotia for too long, they will start to lose some of their neotenous and anthropomorphic traits. They will eventually revert apon returning to Mascotia, although it takes a lot of time for a complete revert to occur.
Another part of the Mascotian Effect is the previously mentioned life-prolonging effect. Creatures living in Mascotia do not age normally, and can have vastly improved lifespans. While disease or accidents may still mow down creatures in their prime, a healthy Mascotian can live up to several millenia of age before showing signs of aging. It is even speculated if Mascotians age at all in this peculiar dimension.
With that being said, creatures dying and being reborn through the Absorbed Realm may contribute to some of the longest lifespans. Some individuals can even recall Mascotia's earliest days, or so they claim.