Finally got the Beastkin lore sorted out for my Impling lore :'D
Sorry it's taken so long!
Writing is not one of my strong points, so it takes me a lot longer to put my ideas into words properly.

Beastkin

The Beastkin, originally Human, live in tribal societies reaching far across most of the known world.

While commonly referred to as Beastkin as a whole, they come in many varying shapes and forms depending on their tribe. Where some tribes have members resembling wolves, with canid faces, feet and tails, another will sprout colorful feathers and more resemble birds.

The number of variations in Beastkin have so far not been fully documented, since while some tribes and individuals settle in towns and cities, many still practice isolated and nomadic lifestyles while living off the land.

A majority of Beastkin still share their ancestors’ shamanistic and spiritual beliefs, giving thanks to their respective deities and paying their respects to the spirits of earth and sky.

As with so many other beliefs however, there’s been no concrete proof that any of these beings exist.

Exactly how the Beastkin became what they are is lost to time, but it’s commonly believed by researchers and historians alike that their shamanistic rituals and beliefs somehow lead them to become the first known example of transformation or metamorphosis via magical means.
Stories told from generation to generation speak of how the shamans of old would perform ritualistic offerings and sacrifices to their animal deities, and by doing so, gaining a part of their strength. Some old records even mention rituals of passage involving drinking the blood of an animal sacrifice.

Regardless of the exact means of this transformation, the permanent physical changes have lead most to consider Beastkin their own species. Not only are they unable to reproduce with their human cousins, but even different Beastkin are often biologically incapable of producing offspring. While many canid forms of Beastkin can interbreed freely, it would appear impossible for an avian to produce a child with a feline, or a cervine with a reptilian.

To go with their beastial apperance, Beastkin are often found to have a slightly higher resistance and affinity towards magical energies in their surroundings, making them a valued asset to research expeditions into more magically active or dangerous areas.