वैश्विक स्तर पर अब तक पहचानी गई और प्रलेखित प्रजातियों की अनुमानित संख्या कितनी है?

Which level of biodiversity is specifically characterized by the variation and differences in genes within individuals of a single species?

Out of the estimated millions of species on Earth, approximately how many species have been scientifically identified and described to date?