Scientists categorize organisms into species based on their physical, genetic, and behavioral characteristics. The most common method for species differentiation is the biological species concept, which defines a species as a population of organisms that can interbreed to produce viable, fertile offspring. According to Jurmain et al., Species is “A group of organisms that can interbreed to produce fertile o spring. Members of one species are reproductively isolated from members of all other species”(28). The biological species concept is “A depiction of a species as a group of individuals capable of fertile interbreeding but reproductively isolated from other such groups”(128).separates one species from another because “Gene exchange between populations (gene flow) will be limited if a geographical barrier, such as an ocean or a large river, effectively separates these populations. This extremely important form of isolating mechanism is called geographical isolation” (128). The ability for some species to interbreed with one another should not be surprising due to the principles of the biological species concept, which categorizes species as groups of organisms capable of fertile interbreeding but reproductively isolated from other such groups. Therefore, due to the biological species concept, two seemingly different and isolated animals such as the domesticated dog and wolf are in fact capable of interbreeding and producing healthy offspring because dogs are known to be descended from the wolf. They share genetic similarities- in the case of dogs and wolves they both possess 78 chromosomes each and are part of the same genus. Although distant, a dog and wolf can interbreed because they are intraspecific, which refers to variation seen within the same species. However, just because the domesticated dog and wolf are capable of interbreed does not guarantee interbreeding due to factors such as geographical isolation. Whereas dogs are domesticated and normally live in civilization with humans, wolves have not been domesticated and live in the wilderness which creates the geographical isolation found today. Due to the geographical isolation dogs and wolves experience from one another; dogs have diverged enough behaviorally to also isolate them so that they no longer willing to interbreed readily. However, because both domesticated dogs and wolves are of the same genus, given favorable conditions such as nonexistent geographical and behavioral isolation, the wolf and domesticated dog can interbreed because the dog is the descendent of the wolf. Paleospecies identifies “Species defined from fossil evidence, often covering a long-time span”(130). For example, when studying extinct fossil primates, it’s necessary to compare them with well-known modern primates. In the case of dogs and wolves, if the dog and the wolf were extinct species and all we had were fossil remains, it will be difficult to identify them as two distinct species. First reason is that they both already fall in the same species. Second reason is that they both are extremely similar, normally it is believed that wolves are bigger than dogs, they have different tail structure, bigger paws, and legs. But the reality is that we have few breeds of dogs which are bigger in size than wolves. Even if we go deep into genetics, we find that they have same chromosome number. So, it could not be possible to separate them in two species on the basis of fossil remains.