From a biological standpoint, Faunus and humans are virtually identical. The two can breed and create fertile offspring, something you can only do if you are the same species. Faunus have every trait humans have, have the same intelligence, digestive systems, and any difference they have, is just something humans lack. Any trait a faunus has varies from faunus to faunus, while humans have nothing. In addition to this, all Faunus have night vision, and usually different enhancements due to their traits. Blake seems to have heightened hearing since she has four ears instead of the standard two, all of which likely connect to the same eardrums. Due to just how similar Faunus and humans are, I personally believe that the traits of the Faunus are the result of an isolated egentic mutation that has been passed down for generations of isolation and breeding with one another. It has been shown that specific faunus traits are not what you inherit, but just the faunus gene. In the WOR episode about Faunus, it has been shown that typically when Humans and Faunus breed, they usually have Faunus children, usually of a trait matching the Faunus parent. This means that the Faunus gene is domiant over the human gene. This also creates some irregularity as when two faunus of different types breed they get a random faunus type. However, I can chalk this up to CRWBY not fully understanding genetics as it makes sense that either regardless of the type of faunus your parents are you coild be any type, or you will match the faunus type with your parents. Overall, in the real world the Faunus gene itself is very similar to a mutation that people can unherit like a vestigial tail, or a sixth finger, albiet pushed to an extreme. I honestly could see an alternate universe where Faunus were a superpowered elite (They have everything that makes them human, plus some exdtra traits.)