分类学

Binomial nomenclature is a two-part naming system for organisms using genus and species names. The genus name is capitalized and italicized, while the species name is lowercase and italicized. For example, the Arctic hare is Lepus arcticus and the jackrabbit is Lepus californicus, allowing scientists to precisely identify and communicate about specific organisms.

Carolus Linnaeus formalized taxonomy in the 18th century by creating a hierarchy of increasingly inclusive categories still used today. He organized organisms from smallest to largest units: species, genus, family, order, class, phylum, kingdom, and domain. This hierarchical system allows scientists to classify all living organisms based on shared characteristics.

Mammalia is defined by the presence of mammary glands that produce milk to nourish offspring. This class includes diverse animals such as humans, polar bears, squirrels, platypuses, kangaroos, and goats. All mammals belong to the phylum Chordata and share this characteristic feature despite their varied appearances and habitats.

Similar species are grouped together into the same genus, representing the smallest meaningful taxonomic unit. The Arctic hare and jackrabbit both belong to genus Lepus but have different species names—arcticus and californicus. This relationship forms the basis of binomial nomenclature, where genus and species together create a unique scientific name.

The domain Eukarya includes animals, plants, fungi, and protists with membrane-bound nuclei and organelles. Bacteria and Archaea are prokaryotes—single-celled organisms lacking nuclei and other membrane-bound structures. These three domains represent the highest taxonomic ranks and reflect fundamental differences in cellular organization and complexity in living systems.

Phylum Chordata is defined by the presence of a notochord, a flexible, rod-like structure found in chordate embryos. All vertebrate animals, including mammals, birds, reptiles, amphibians, and fish, belong to this phylum. The notochord is a key structural feature that distinguishes chordates from other animal phyla.

Hares and rabbits belong to the family Leporidae, while pikas belong to the family Ochotonidae. Despite different families, all three groups share the same order, Lagomorpha, and class, Mammalia. Pikas resemble hares and rabbits but have smaller, rounder bodies and no visible tail, illustrating how taxonomy groups organisms by both similarities and differences.