17.1 The History of Classification
Early Systems of Classification (cont.)
Aristotle's System - Greek philosopher , Aristotle (394-322 B.C.) - Developed the first widely accepted system. - Classified organisms as either plants or animals.
Early Systems of Classification
Classification - is the grouping of objects or organisms based on a set of criteria. - Biologists find it easier to communicate and retain information about organisms when the organisms are organized into groups. - One of the principal tools for this is biological classification.
Taxonomic Levels
Domain Kingdom Phylum Class Order Family Genus Species Scientific name
Human Taxonomic Levels
Domain: Eukarya Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primata Family: Hominidae Genus: Homo Species: Sapien Scientific name: Homo sapien
Early Systems of Classification (cont.)
Limitations of Aristotle's System: - Viewed systems as being distinct, separate, and unchanging. - This was a common view until Darwin presented his theory of evolution which stated that organisms are always changing. Organisms share evolutionary relationships. - Nevertheless, many centuries passed before Aristotle's System was replaced by a new one that was better suited to the increased knowledge of the natural world.
Taxonomy
The discipline of... 1. Classifying organisms 2. Assigning each organism a scientific name
genus
taxonomic group of closely related species with a common ancestor
domain
taxonomic group of one or more kingdoms
phylum
taxonomic group of related classes
kingdom
taxonomic group of related phyla or division
family
taxonomic group of similar, related genera that is smaller than a genus and and larger than an order
class
taxonomic group that contains one or more related orders
order
taxonomic group that contains related families
division
taxonomic term used instead of phylum to group related classes of plants and bacteria
Taxonomic Categories (Created by Linnaeus)
Species and Genus Taxon - a named group of organisms (plural, taxa). - Range from having broad diagnostic characteristics to having specific characteristics. - Think of taxa as a set of nesting boxes - one fitting inside the other. - Domain - Kingdom - Phylum - Class - Order - Family - Genus - Species
taxon
named group of organisms, such as phylum, genus or species
Linnaeus's System
- (1707-1778) - Swedish naturalist - Broadened Aristotle's classification method and formalized it into a scientific system - He based his system on observational studies of the morphology and the behavior of organisms - His system was the first formal system of taxonomic organization - Linnaeus's method of naming organisms, called binomial nomenclature, set his system apart from Aristotle's system and remains today.
Aristotle's System
- (394-322 B.C.) - Greek philosopher - Developed the first widely accepted system of biological classification - Classified organisms as either animals or plants - Animals were classified according to their presence or absence of red-blood - Animals were further grouped according to their habits and morphology - Plants were classified by average size and structure as trees, shrubs, or herbs
What is a family?
- A family is a group of genera that have similar characteristics. - All bears, both living and extinct, belong to the family Ursidae. - All members of the Ursidae family have similar characteristics. - For example, they walk flat-footed and have forearms that can rotate to grasp prey closely.
What are the higher taxa?
- An order is a group of families that have similar characteristics. - A class is a group of one or more related orders. A phylum or a division is a group of related classes. - The term division is used for bacteria and plants. - A kingdom is a group of related phyla, or domains. - The least specific of all taxa is a domain. - A domain is a group of one or more kingdoms.
What were the limitations of Aristotle's system of classification?
- Aristotle's system of classification was useful for organizing, but it had many limitations. - One limitation was that Aristotle's system was based on his understanding that species are distinct, separate, and unchanging. - Because of this understanding, Aristotle's classification did not account for evolutionary history or relationships. - Also, many organisms have been discovered that do not fit Aristotle's classification system, such as birds that do not fly and frogs that live on land and in water. - Aristotle's system was used for many centuries before it was replaced by a new system. - The new system built on the knowledge humans had gained about the natural world.
Section 17.1 - The History of Classification
- Biologists use a system of classification to organize information about the diversity of living things. - Just as stores group CDs according to type of music and artist, biologists group living things by their characteristics and evolutionary relationships.
Why do scientists use scientific names?
- Biologists use scientific names because common names vary in their use. - For example, the bird Cardinalis cardinalis, is commonly called a redbird, a cardinal, and a Northern cardinal. - Binomial nomenclature is also used because common names can be misleading. - A starfish is neither a star nor a fish, a great horned owl does not have horns, and a sea cucumber is not a plant. - When writing scientific names, scientists follow certain rules. The most important rules are as follows: • The first letter of the genus name is always capitalized, but the rest of the genus name and all of the specific epithets are lowercase. • If a scientific name is printed in a book or magazine, it is italicized. • If a scientific name is written by hand, it is underlined. • After the complete scientific name has been written once, the genus name will often be abbreviated to the first letter when used again. For example, the scientific name Cardinalis cardinalis can be written C. cardinalis
How did Linnaeus classify organisms?
- In the eighteenth century, Swedish botanist Carolus Linnaeus developed a branch of biology called taxonomy. - Taxonomy is a discipline of biology concerned with identifying, naming, and classifying species based on the morphological and behavioral similarities and differences of organisms. - Linnaeus's system built on the foundation of Aristotle's system of classification. - Linnaeus used similarities and differences in morphology and behavior to classify birds. - The morphological differences can be related to differences in where the birds lived and their behavior
Early Systems of Classification
- It is easier for biologists to communicate and keep information about organisms when the organisms are organized into groups. - One tool biologists use to organize organisms is classification. - Classification is the grouping of objects or organisms based on a set of conditions. - A regular system of classification helps scientists organize and communicate information about biology.
How are scientific names written?
- Linnaeus named organisms using binomial nomenclature. - Binomial nomenclature gives each species a scientific name that has two parts. - The first part is the genus name, and the second part is the specific epithet, or specific name, that identifies the species. - Latin is often used for binomial nomenclature because Latin is a language that is unchanging. - Historically, Latin has also been the language of science. - The meaning of Latin words can be understood by scientists who speak different languages.
How has the classification system changed?
- Linnaeus's classification system made it possible to include evolutionary principles in classification in the 1800s. - In the nineteenth century, important scientists, including Jean-Baptiste Lamarck, Charles Darwin, and Ernest Haeckel, introduced classification systems based on evolutionary relationships to organize biological diversity. - Categories used in modern classification are based on Linnaeus's system but have been changed to show evolutionary relationships.
Early Systems of Classification (cont.)
- Linnaeus's method of naming organisms called binomial nomenclature - gives each species a two-part name: genus and species - Latin - Cardinalis cardinalis
3 ways to name organisms
- Location - Characteristics: like color, shape, size... - Discoverer
How did Aristotle classify organisms?
- More than two thousand years ago, Aristotle, a Greek philosopher, developed the first commonly accepted system of biological classification. - Aristotle classified organisms as either animals or plants. - Animals were classified by their habitat and their morphology. - Morphology relates to the physical characteristics and structures of organisms. - Animals were also classified by the presence of red blood. - Aristotle's classification of "bloodless" and "red blood" animals closely matches today's classification of invertebrates and vertebrates. - Plants were classified by average size and structure—as trees, shrubs, or herbs.
The Taxonomic Categories (cont.)
- Order - contains related families - Class - contains related orders - Phylum - (pl. phyla) or division (bacteria and plants) contains related classes - Kingdom - the taxon composed of related phyla or divisions - Domain - the broadest of taxa.
The Taxonomic Categories
- Species - a group of organisms that can interbreed and produce offspring. [Ursus americanus (American black bear), Ursus thibetanus (Asiatic black bear)] - Genus - (pl. genera) a group of species that are closely related and share a common ancestor. (Ursus = black bear) - Family - is the next higher taxon, consisting of similar, related genera. (Ursidae = all bears, both living and extinct; brown bears, polar bears, giant pandas) -All members of the bear family share certain characteristics. They walk flatfooted, have forearms that can rotate to clasp prey.
Aristotle's System Limitations
- System was baed on his view that species are distinct, separate, and unchanging - Because of his understanding of species, Aristotle's classification does not account for evolutionary relationships - Many organisms do not fit easily into Aristotle's system, such as birds that don't fly or frog that live both on land and in water
Systematics Applications
- Systematicists are scientists who study classification. - They provide detailed guides that enable other people to identify organisms. - Many times, field guides have dichotomous keys, which are keys based on a series of choices between characteristics. - You can tell if a plant or animal is poisonous by using a field guide to identify it. - Systematicists also work to identify new species and relationships among known species. - If a known species produces a certain chemical, a close relative might produce a similar chemical.
Taxonomic Categories
- Taxonomists classify organisms by dividing them into smaller groups based on more specific criteria. - Taxonomic categories used by scientists are like nesting boxes—each category fits into another. - The categories are arranged from broadest to most specific. - A named group of organisms is called a taxon (plural, taxa).
Dichotomous Keys
- Taxonomists have developed special guides known as dichotomous keys to aid in identifying unknown organisms. - A dichotomous key consists of several pairs of descriptive statements that have only two responses.
What is systematics?
- Taxonomy is part of a larger branch of biology called systematics. - Systematics is the study of biological diversity. - Scientists study diversity in the past, as well as present biological diversity.
What are a species and a genus?
- Two of the taxa Linnaeus used were genus and species. - Today, a genus (plural, genera) is defined as a group of species that are closely related and share a common ancestor. - A species is a group of organisms that have similar characteristics such as skull shape and size. For example, the species American black bear (Ursus americanus) and the species Asiatic black bear (Ursus thibetanus), shown below, belong to genus Ursus. - All species in the genus Ursus have massive skulls and similar tooth structure.
Rules for naming
1. First word is capitalized 2. Second word is lowercased 3. Both words are written in italics
Binomial nomenclature
2 word naming system - A scientific name describes organisms
Early Systems of Classification (cont.)
Linnaeus's System: - Linnaeus (Swedish Naturalist, 1707-1778) - Broadened Aristotle's classification method - Concentrated on morphology and behavior of organisms - Categorized birds into three major groups - Linnaeus's system of classification was the first formal system of taxonomic organization. Taxonomy - is a discipline of biology primarily concerned with identifying, naming, and classifying species based on natural relationships.
binomial nomenclature
Linnaeus's system of naming organisms, which gives a specific two-word Latin name to each species - the first part is the genus name and the second is the specific epithet
Dichotomous Key
a series of physical statements that describe physical characteristics of different organisms/objects - help to organize organisms
taxonomy
branch of biology that identifies, names, and classifies based on their natural relationships
classification
grouping of organisms or objects based on a set of criteria that helps organize, communicate, and retain information
Classification
grouping system based on a set of criteria