The majority of Terra's civilization consists of the Ancients: a conglomeration of sapient races consisting of those resembling the Homo sapiens of Earth with the body parts of various animals, legendary creatures, and mythological beings in our world, notably ears and tail; and bipedal, sentient animals/legendary creatures/mythological beings. For the sake of practicality, the Arknights Fandom Wiki refers to the former as "humanoid Ancients" and the latter as "anthropomorphic Ancients".
Certain humanoid Ancients have two pairs of ears, one human and one animal, and both are functional. Furthermore, the Ancients' humanoidism and anthropomorphism are apparently not tied into their bloodline, which can be explained by the anthropomorphic Rat King having a humanoid daughter (Lin Yühsia).
The term human and its derivatives are typically used to refer to the Ancients as a whole; "Ancient" itself is only used in technical circumstances by the Terrans. Despite this nomenclature and the fact that humanoid Ancients share a superficially similar appearance with Homo sapiens, both are completely distinct races.
In Guiding Ahead, it has been stated that the child of a Sankta and an individual of another race will always inherit the other parent's race (e.g. if a Sankta and a Forte had a child, the child will always be a Forte). However, a half-blood child between a Sankta mother and a Sarkaz father was shown to have the traits of a Sankta (wings and a halo), which brings the validity of this claim into question.