Naming in Biology

Each species has a unique scien­tific name that positively identi­fies it. The system avoids the dif­ficulties with common names that can vary from place to place and language to language. The words in scientific names are either Latin or latinized.
Each species is given two names, one for the species itself and the other for the genus (plu­ral genera), the group of related species to which the organism be­longs. Both terms are italicized, and the genus name is capital­ized. For example, the wolf is Canis lupus, and the domestic dog is Canis familiaris. A close rela­tionship between these two spe­cies is shown by placing both in the genus Canis. Sometimes a ge­nus consists of only one species. Thus the only present-day mem­ber of the genus Homo is our spe­cies, Homo sapiens. Once a spe­cies has been fully identified in a discussion, the generic term may be abbreviated-for example, H. sapiens.
This system is part of a larger scheme for classifying organisms. The scheme traces to a Swedish botanist, Carolus Linnaeus, who based his classification on what he thought were levels of complexity in the order of nature. To Linnaeus, in 1756, these levels seemed part of the Creator's mas­ter plan. But most present-day bi­ologists believe that the similari­ties Linnaeus recognized reflect evolutionary relationships rather than preordained levels of com­plexity. In other words, similar organisms are closely related to each other, and they share a rela­tively recent common ancestor.
Although some of Linnaeus's basic assumptions are no longer accepted, his scheme of organiza­tion remains useful. The present­day classification system, based on the Linnaean scheme, is com­posed of large groups, each of which is subdivided again and again into smaller units of in­creasing similarities. Consider the classification of humans.
Kingdom: Animalia (all ani­mals, including jellyfish and oysters)
Phylum: Chordata (includes mammals, fish, birds, frogs, and many more)
Class: Mammalia (rats, ele­phants, cows, and primates, too)
Order: Primates (monkeys, bush babies, and others in addi­tion to humans)
Family: Hominidae Genus: Homo
Species: Homo sapiens
Except for species, biologists recognize that these categories are arbitrary. For example, there are no absolute criteria for lumping species into a genus. One author­ity can legitimately divide ten re­lated species into seven genera, whereas another authority on the same group places the ten species in only two genera. Both are making their decisions on degr_ees of similarities. But because each species is unique, there can be no rule to determine exactly how similar species must be to be placed in the same genus. Thus genera and higher categories are only convenient ways to catalog the tremendous number of spe­cies and to reflect what is be­lieved to be their evolutionary history.
In contrast, species have a biological reality. Members of a species will interbreed in nature only with members of the same species. Every spe­cies consists of members
with characteristics unique to that species.