Biologists classify organisms into different groups and the most basic of these groups is the species. A species is not defined by its location nor its appearance, although these can be helpful clues, but by whether or not the members of this group are capable of interbreeding and producing fertile young. (Jurmain, R., Kilgore, L., Trevathan, W., Bartelink 2017 p. 4). This view is called the biological species concept. These differing groups are formed through the evolutionary process of speciation. Speciation is a product of geographic isolation. Once members of a species are isolated from each other and unable to exchange genes, their differences will magnify. Even if they are not subject to the different environmental pressures necessary to natural selection, these different populations will still experience genetic drift, altering their allele frequencies, and, possibly, experience mutation. When the environmental pressures of natural selection are added to this process, these differences are greatly magnified (Jurmain et al 2017 p. 100 ). Because even small changes to genes can result in major changes to a phenotype (Jurmain et al 2017 p. 106), these species will start to differ. If they are denied gene flow, these different groups of organisms, will eventually become incapable of fertile interbreeding. They will become different species.But this biological classification of species has some gray areas. Some species can interbreed and produce fertile young. While wolves (Canis lupus) and dogs (Canis familiaris) are classified as different species, they are members of the same genus and closely enough related that they can engage in fertile interbreeding. This is not surprising because dogs are recently descended from wolves and therefore have much in common with them. They share a very similar genotype and are not prevented from breeding by behavioral isolation. As with most classifications, the biological species concept is a general rule. Speciation is the end result of a process but it is a process and this process can be reversed through genetic flow. As different groups undergo speciation, there will be periods of time when they can still mate with each other. There will also be genetic differences in the individuals of different groups that may allow for fertile interbreeding with individual members of a different species and, the closer these species are, the more likely these differences become. Some hybrid young can reproduce. Even in human history, it is, due to changes on the X chromosome, theorized that it might have taken ancestral humans and chimpanzees approximately four million years to achieve a full split into different species. During this long process, they were mating with each other and producing hybrids (Carey, B, 2006). The biological classification of species may seem solid but it can be a little fuzzy around the edges. But so can macroevolutionary processes and our applied understanding of them.We can detect some of this fuzziness in our categorization of different paleospecies. A paleospecies is “a species defined from fossil evidence, often covering a long time span.” (Jurmain et al 2017 p. 107) If all we had of Canis lupus and Canis familiaris were fossils, we might or might not define them as the same species. Much would depend on the condition of the fossils and their location in space and time. Our classificationwould also depend on what example of Canis familiaris we found. Even two different examples of Canis familiaris, the bulldog and the saluki, would likely be classified as different paleospecies because of their differences in snouts and cranial vaults. (West LA College, 2018). One could imagine this problem growing even more complicated. A small and wolf-like dog, such as a miniature husky, may appear to be a young, diseased or malnourished wolf. If its fossil was separated from the wolf fossil by a lot of time or space or both, and there were no other wold fossils to be found, this miniature huskycould even appear to be an evolution of the wolf. But if a regular husky fossil was found near a wolf fossil, these two animals could be reasonably be believed to be members of the same species due to their many similarities in skull shape and dentition. Homoplasy is a complicated matter. When applied to fossils, it becomes even more complicated.