18.1 Finding Order in Diversity Ch. 18 Classification 18.1 Finding Order in Diversity

THINK ABOUT IT Scientists have been trying to identify, name, and find order in the diversity of life for a long time. The first scientific system for naming and grouping organisms was set up long before Darwin. In recent decades, biologists have been completing a changeover from that older system of names and classification to a new strategy based on evolutionary theory.

Assigning Scientific Names The first step in understanding and studying diversity is to describe and name each species. By using a scientific name, biologists can be sure that they are discussing the same organism. Common names can be confusing because they vary among languages and from place to place. For example, the names cougar, puma, panther, and mountain lion can all be used to indicate the same animal— Felis Concolor.

Assigning Scientific Names In the eighteenth century, European scientists agreed to assign Latin or Greek names to each species. Early scientific names often used long phrases to describe species in great detail. For example, the English translation of the scientific name of a tree might be “Oak with deeply divided leaves that have no hairs on their undersides and no teeth around their edges.” It was also difficult to standardize names because different scientists focused on different characteristics

Binomial Nomenclature In the 1730s, Swedish botanist Carolus Linnaeus developed a two-word naming system called binomial nomenclature. The scientific name usually is Latin. It is written in italics. The first word begins with a capital letter, and the second word is lowercased.

Copyright Pearson Prentice Hall Ursus arctos (grizzly bear) Ursus americanus (black bear) The first part of the name is the genus to which the organism belongs. A genus is a group of closely related species. The genus name is capitalized. The second part of the name is unique to each species within the genus. This part of the name often describes an important trait or where the organism lives. The species name is lowercased. Copyright Pearson Prentice Hall

Classifying Species into Larger Groups In addition to naming organisms, biologists try to organize, or classify, living and fossil species into larger groups that have biological meaning. Biologists often refer to these groups as taxa (singular: taxon). The science of naming and grouping organisms is called systematics. Previously, it was referred to as taxonomy.

Linnaean Classification System Linnaeus also developed a classification system that organized species into a hierarchy, or ranking. In deciding how to place organisms into larger groups, Linnaeus grouped species according to anatomical similarities and differences.

Seven Levels Linnaeus identified just four levels in his original classification system. Over time, Linnaeus’s original classification system would expand to include seven taxa: species, genus, family, order, class, phylum, and kingdom.

Copyright Pearson Prentice Hall  Species and genus are the two smallest categories. Grizzly bear Black bear Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Genera that share many characteristics are grouped in a larger category, the family. Grizzly bear Black bear Giant panda Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall An order is a broad category composed of similar families. This order also contains the families Canidae (dogs) and Felidae (cats). Grizzly bear Black bear Giant panda Red fox Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The next larger category, the class, is composed of similar orders. All mammals are warm-blooded, have body hair, and produce milk for their young. Grizzly bear Black bear Giant panda Red fox Abert squirrel Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Class Mammalia Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Several different classes make up a phylum. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake PHYLUM Chordata Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The kingdom is the largest and most inclusive of Linnaeus's taxonomic categories. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake Sea star KINGDOM Animalia Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Problems With Traditional Classification In a way, members of a species determine which organisms belong to that species by deciding with whom they mate and produce fertile offspring. Ranks above the level of species, however, are determined by researchers who decide how to define and describe genera, families, orders, classes, phyla, and kingdoms. Linnaeus grouped organisms into larger taxa according to overall similarities and differences. But which similarities and differences are the most important?

Problems With Traditional Classification Modern classification schemes look beyond overall similarities and differences and group organisms based on evolutionary relationships.