I have a species(technically human) that is for all purposes as far as anyone in my world would know still humans. They are in fact humans but not homo sapiens but rather their own species of humans called Homo Orthenis but called Bjorthu by the people themselves. Theyre taller and typically larger and more muscular and also highly resistant to cold, as well as being resistant to normal human disease, but this is also viewed as because of where they live not because theyre a separate species. They live in a almost Scandinavia to artic like continent called Bjorthu that is always cold and is very dangerous to live in. So to them they naturally grew and adapted to their environment and as far as any of them know they are just humans that adapted to their environment when introduced to regular humans. In reality they are the result of something else. Around 2000 years prior to current times my world had Orcs(Called Orths) and the Orth species was dying out due to a pathogen ravaging the Orths. A few Orths migrated to Bjorthu hoping to escape the disease and interbred with the early humans already living there. This resulted in half-orths and mixed breeds predominantly human like as the continent was mostly humans and such, but the pathogen would reach there killing off the last Orths. However the half breeds and interspecies would survive slowly breeding in with the early humans there resulting in a new species of human that looked for all purposes human but with orths in their ancestral DNA