CLASSIFICATION (of LIVING THINGS) AND EVOLUTION IN PROCESS

HISTORY OF TAXONOMY

Every year, thousands of new species are discovered.  Biologist use characteristics of each newly discovered species to classify it with organisms having similar characteristics.  The way we group organisms continue to change, and today these methods reflect the evolutionary history of organisms.

OBJECTIVES: Describe Aristotle's classification system, and explain why it was replaced. Explain Linnaeus's system of classification, and identify the main criterion he used to classify organisms.  List Linnaeus's levels of classification from the most general to the most specific.  Name the primary criterion that modern taxonomist consider when they classify organisms. Explain why scientific names are more useful to scientist than common names.

1. SCIENTISTS HAVE IDENTIFIED MORE THAN 2 MILLION SPECIES OF ORGANISMS ON EARTH, BUT ESTIMATE 40 MILLION SPECIES INHABIT THE EARTH.

2. SOME ESTIMATE THAT THERE MAY BE MILLIONS OF SPECIES IN THE TROPICAL RAIN FOREST AND AN UNSPECIFIED NUMBER LIVING IN THE OCEANS YET UNDISCOVERED.

3. WE HAVE A CLASSIFICATION SYSTEM TO:

    A.  ASSIGNED A SINGLE UNIVERSAL NAME TO EACH ORGANISM.

    B.  TO PLACE ORGANISMS INTO GROUPS THAT HAVE REAL BIOLOGICAL MEANING.

4. The modern system of biological Classification Organizes information about Living Things by placing them in GROUPS.

5. The Field of Biology that deals with classifying organisms is called TAXONOMY or Systematic Biology.  Taxonomy Names and Groups Organisms According to their Characteristics and Evolutionary History.

6. A Universal System is necessary to have clear communication among scientists worldwide. A system that required an International System for Classifying and Naming all organisms.

7. This System was designed to Eliminate the use of Common Names and Confusion in the Scientific World.

8. Organisms were First Classified more than 2,000 years ago by Greek philosopher Aristotle.  He classified things as either Plant or Animal.

9. He grouped animals into Land Dwellers, Water Dwellers, and Air Dwellers.

10. He also grouped Plants into three categories, based on differences in their Stems.

11. As modern science developed in the fifteenth and sixteenth centuries, Aristotle's system was INADEQUATE.

12. They also found that Using COMMON NAMES, such as robin or fir tree, for an organism presented its own problems;  common names varied from on locale to the next and common Names May Not describe species accurately.

13. Carl VON Linne, (Carols Linnaeus) mid-1700s, Swedish Biologist established a simple system for classifying and naming organisms. He developed a Hierarchy (a ranking system) for classifying organisms that is the Basis for Modern Taxonomy.

14. Linnaeus used an organisms MORPHOLOGY, that is its Form and Structure, to categorize it.  His system is still being used today.

15.  Linnaeus established a system of groups called TAXA. (TAXON)

16. EACH TAXON IS A CATEGORY INTO WHICH RELATED ORGANISMS ARE PLACED.

17. Linnaeus used Latin for the Names of the Taxa, because this was the language of educated people and not an everyday language likely to change.

18. Linnaeus is the Father of Modern Taxonomy.

19. Linnaeus based his system upon STRUCTURAL SIMILARITIES BETWEEN ORGANISMS.

20. THE SYSTEM OF CLASSIFICATION LINNAEUS DEVELOPED IS A HIERARCHY, OR RANKING SYSTEM.

21. In his system of classification, he ranked the categories from the Broadest and Most General TAXA (THE TWO KINGDOMS - PLANTS AND ANIMALS) to the Smallest and Most Specific TAXA (INDIVIDUAL SPECIES).

22. He first divided all organisms into TWO GROUPS, PLANTS AND ANIMALS. THAT WERE CALLED KINGDOM PLANTAE AND ANIMALIA.

23. HE THEN BROKE DOWN EACH GROUP AS FOLLOWS:

    A.  EACH KINGDOM INTO SMALLER GROUPS CALLED CLASSES.

    B.  EACH CLASS WAS DIVIDED INTO ORDERS.

    C.  EACH ORDER WAS DIVIDED INTO GENERA (GENUS)

    D.  AND GENERA WERE DIVIDED INTO SPECIES.

24. EACH LEVEL GROUPS TOGETHER ORGANISMS THAT SHARE MORE CHARACTERISTICS WITH EACH OTHER.

BINOMIAL NOMENCLATURE

1. Linnaeus's classification hierarchy included five levels (KINGDOM, CLASS, ORDER, GENUS, AND SPECIES). Modern scientist have added TWO more classifications levels to the original five (PHYLUM AND FAMILY).

2. Today we have SEVEN LEVELS OF CLASSIFICATION: 

    A. KINGDOM
    B. PHYLUM (DIVISION - IN THE PLANT KINGDOM)
    C. CLASS
    D. ORDER
    E. FAMILY
    F. GENUS
    G. SPECIES

3. KING PHILIP CAME OVER FOR GRANDMA'S SOUP.

4. Linnaeus proposed a system of Scientific Naming using TWO NAMES FOR EVERY ORGANISM: THE GENUS AND THE SPECIES NAME.

5. To ensure accurate communication of information, biologist assigns a unique two-word scientific name to each organism. (BINOMIAL NOMENCLATURE)

6. IDENTIFYING ORGANISMS BY THEIR GENUS AND SPECIES NAMES IS CALLED THE BINOMIAL SYSTEM, OR BINOMIAL NOMENCLATURE. ("TWO-NAME NAMING)

7. They used names based on Latin or Ancient Greek words - scientist everywhere understood these languages.

8. The FIRST Word of the Scientific Name (Species Name) is the name of the GENUS to which the organism belongs.

9. The Genus name refers to the relatively small group of organisms to which a particular type of organism belongs.

10. The SECOND part of the name is the SPECIES. (SPECIES IDENTIFIER) The Species name is usually a Latin description of some important characteristic of the organism.

11. When we use the Latin name for an organism, we Always Capitalize the Genus but Not the Species Identifier. We also print the name in Italics or Underline them.

    SAMPLE:  Acer rubrum - RED MAPLE TREE

    Acer is the Latin name for Maple (genus)

    rubrum is the Latin word for Red (species)

    OR THE NAME CAN BE ABBREVIATED AS:
           A. rubrum.

    HUMANS ARE NAMED: Homo sapiens

    Homo because of our large brain and upright posture.
    sapiens because of our intelligence and ability to speak.

12. Botanist sometimes split species into Subsets known as VARIETIES.  Bacteria are also broken into subsets called STRAINS.

13. To classify organisms, modern Taxonomist consider the PHYLOGENY, OR EVOLUTIONAL HISTORY OF THE ORGANISM. DNA.
 

MODERN PHYLOGENETIC TAXONOMY

1. When placing an organism into a Taxonomic Category, Modern Taxonomists May consider its:

    • MORPHOLOGY
    • CHROMOSOMAL CHARACTERISTICS
    • NUCLEOTIDE (DNA AND RNA) AND AMINO ACID SEQUENCES – MOLECULAR   BIOLOGY*
    • EMBRYOLOGICAL DEVELOPMENT (SEE PICTURE BELOW).
    • FOSSIL RECORD

EARLY EMBRYOS OF MANY DIFFERENT VERTEBRATE SPECIES LOOK REMARKABLY SIMILAR. THESE SIMILARITIES IN EARLY EMBRYOLOGICAL DEVELOPEMNT OF VERTEBRATES CAN BE TAKEN AS ANOTHER INDICATION THAT VERTEBRATES MAY SHARE A COMMON ANCESTRY.

All of the above are used to yield reliable information about the PHYLOGENY or Evolutionary History of an organism.

2. TWO APPROCHES: BOTH BASED ON HYPOTHESIS

    A. SYSTEMATICS – PHYLOGENETIC TREE (FAMILY TREE) – WHICH SHOWS RELATIONSHIPS THOUGHT TO EXISTS AMONG GROUPS OF ORGANISMS.  

    B. CLADISTICS –  CLADOGRAMS - NEW SYSTEM OF PHYLOGENENTIC CLASSIFICATION. USES CERTAIN FEATURES OF ORGANISMS, CALLED SHARED DERIVED CHARCTERS, TO ESTABLISH EVOLUTIONARY RELATIONSHIPS.

A DERIVED CHARACTER IS A FEATURE THAT APPERENTELY EVOLVED ONLY WITHIN THE GROUP UNDER CONSIDERARATION.

EXAMPLE: IF THE GROUP CONSIDERED IS BIRDS, ONE EXAMPLE OF A DERIVED CHARACTER IS FEATHERS.

MOST ANIMALS DO NOT HAVE FEATHERS; BIRDS ARE THE ONLY ANIMALS THAT DO.

IT IS SAFE TO ASSUME THAT FEATHERS EVOLVED WITHIN THE BIRD GROUP AND WERE NOT INHERITED FROM SOME DISTANT ANCESTOR OF THE BIRDS.
 

TWO MODERN SYSTEMS OF CLASSIFICATION

 Aristotle classified organisms as either plant or animal, but today we recognize that many forms of life are neither.

OBJECTIVES:  Describe the six-kingdom system of classification.  List the characteristics that distinguish archaebacteria from eubacteria.  Explain why protists are group together in the six-kingdom system in spite of having differences that are greater than those between plants and animals.  Describe evidence that prompted the creation of the three-domain system of classification.  Explain the principal difference between the six-kingdom system and the three-domain system of classification.

THE SIX-KINGDOM SYSTEM

1. Linnaeus classified all organisms into TWO KINGDOMS, PLANTAE AND ANIMALIA.

2. Modern TAXONOMIST recognizes that many organisms are Neither Plant or Animal. Most Taxonomist use the SIX-KINGDOM SYSTEM.

3. THESE SIX KINGDOMS GROUP ORGANISMS TOGETHER THAT HAVE SIMILARITIES IN SUCH FUNDAMENTAL CHARACTERISTICS AS MAJOR CELLULAR STRUCTURE, METHODS OF OBTAINING NUTRIENTS, AND METABOLISM.

4. TODAY'S SIX KINGDOMS ARE: ARCHAEBACTERIA, EUBACTERIA, PROTISTA, FUNGI, PLANTAE, AND ANIMALIA. 

5. KINGDOM ARCHAEBACTERIA:  The prefix archae - comes from the Greek Word "ANCIENT".  Modern Archaebacteria MAY BE Directly descended from and very similar to the First Organisms on Earth.  They Are UNICELLULAR PROKARYOTES with distinctive Cell Membranes as well as Biochemical and Genetic Properties that Differ from ALL Other Kinds of Life.  Some are AUTOTROPHIC, producing food by CHEMOSYNTHESIS. Most are HETEROTROPHIC.  Many Archaebacteria LIVE in HARSH ENVIRONMENTS such as Sulfurous Hot Springs, Very Salty Lakes, and in ANAEROBIC Environments, such as the Intestines of Mammals. Includes Chemosynthetic Bacteria.

6. KINGDOM EUBACTERIA: The EU part of Eubacteria means "TRUE".  They are UNICELLULAR PROKARYOTES.  Most of the Bacteria (Germs) that affect your life are members of the Kingdom Eubacteria.  Eubacteria are both AUTOTROPHS and HETEROTROPHS. Includes the Diesease-Causing Bacteria such as tooth decay or food poisoning.

The Combined Kingdoms, Archaebacteria and Eubacteria include the Greatest Number of Living Things on Earth.  ALL OF THE PROKARYOTES ARE IN THESE TWO KINGDOMS. Both Reproduce By Binary Fission, but they do have some ways to Recombine Genes, allowing Evolution (CHANGE) to occur.

7. KINGDOM PROTISTA: "THE ASH AND TRASH KINGDOM". These organisms are placed here more because of What They Are Not than What They Are.  Kingdom Protista contains All Eukaryotes that are NOT Plants, Animal, or Fungi, more than 50,000 Species in all. Kingdom Protista includes UNICELLULAR and a few simple MULTICELLULAR EUKARYOTES. Eukaroyotic cells have nuclei and organelles that are surrounded by membranes. The cells of multicellular protists are not specialized to perform specific functions in the organisms. Includes Euglena and Amoebas.

8. KINGDOM FUNGI. Fungi are Eukaryotes, and most are MULTICELLULAR. The cells of fungi have cell walls that contain a material called CHITIN. These organisms are HETEROTROPHIC AND OBTAIN THEIR NUTRIENTS BY RELEASING DIGESTIVE ENZYMES INTO A FOOD SOURCE. They absorb their food after it has been Digested by the Enzymes. Fungi act either as DECOMPOSERS OR AS PARASITES IN NATURE. KINGDOM FUNGI INCLUDES MOLDS, MILDEWS, MUSHROOMS, AND YEAST.

9. KINGDOM PLANTAE. Plants are EUKARYOTE, MULTICELLULAR and carry out PHOTOSYNTHESIS (AUTOTROPHS). The cells of plants have CELL WALLS, that contain the POLYSACCHARIDE CELLULOSE. PLANT CELLS ARE SPECIALIZED FOR DIFFERENT FUNCTIONS, SUCH AS PHOTOSYNTHESIS, THE TRANSPORT OF MATERIALS, AND SUPPORT. KINGDOM PLANTAE INCLUDES MOSSES, FERNS, CONE-BEARING PLANTS (GYMNOSPERMS), AND FLOWERING PLANTS (ANGIOSPERMS).

10. KINGDOM ANIMALIA. Animals are MULTICELLULAR, EUKARYOTES, AND HETEROTROPHIC. Animal cells have NO CELL WALLS. Most members of the Animal Kingdom can move from place to place. Some are Permanently attached to surfaces such as Sponges and Barnacles. FISH, BIRDS, REPTILES, AMPHIBIANS, AND MAMMALS-INCLUDING HUMANS BELONG TO THE KINGDOM ANIMALIA. THIS KINGDOM ALSO INCLUDES SPONGES, JELLYFISH, WORMS, SEA STARS, AND INSECTS.

RELATIONSHIPS BETWEEN THE SIX KINGDOMS

THREE-DOMAIN SYSTEM

1. The young Science of Molecular Biology has led to an alternative to the Six-Kingdom System.

2. This system is based on comparing sequences of RIBOSOMAL RNA in different organisms, to determine organisms common ancestry.

3. The PHYLOGENTIC TREE (FAMILY TREE) drawn from this data show that Living Things SEEM to fall naturally into Three Broad Groups, or DOMAINS:

    A. DOMAIN ARCHAEA - is known in the Six-Kingdom System as Kingdom Archaebacteria. The Chemosynthetic Bacteria.

    B. DOMAIN BACTERIA - Equals Kingdom Eubacteria. The Disease-Causing Bacteria.

    C. DOMAIN EUKARYA - consists of the protists, the fungi, and the plants and animals.  All Eukaryotes have true nuclei with linear chromosomes and membrane-bound organelles.  Most of the variation in this domain is among the protists.

BELOW IS A PHYLOGENIC TREE OR FAMILY TREE USED TO SHOW THE EVOLUTIONARY RELATIONSHIP THOUGHT TO EXIST AMOUNG GROUPS OF ORGANISMS. A PHYLOGENIC TREE REPRESENTS A HYPOTHESIS, AND IS GENERALLY BASED ON SEVERAL LINES OF EVIDENCE SUCH AS THE FOSSIL RECORD, MORPHOLOGY, EMBRYOLOGICAL PATTERNS OF DEVELOPMENT, AND CHROMOSOME AND MACROMOLECULES.

SEE THE CLADOGRAM USED IN CLADISTIC TAXONOMY, WHICH SHOWS RELATIONSHIPS OF ORGANISMS BASED ON SHARED DERIVED CHARACTERISTICS TO ESTABLISH EVOLUTIONARY RELATIONSHIPS. TO INTERPRET A CLADOGRAM, BEGIN AT THE BOTTOM AND MOVE UP THE AXIS THAT SHOW THE BRANCH POINTS. GROUPS AND DERIVED CHARACTERS APPEAR IN THE ORDER SHOWN.

EVOLUTION IN PROCESS

SIMILAR FEATURES THAT ORIGINATE IN A SHARED ANCESTOR ARE DESCRIBED AS HOMOLOGOUS FEATURES. COMPARE THE FORLIMBS SHOWN BELOW, ALTHOUGH THE LIMBS LOOK DIFFERENT AND VARY GREATLY IN FUNCTION, THEY ARE VERY SIMILAR IN SKELETAL STRUCTURE, AND THEY DERIVED FROM THE SAME STRUCTURES IN THE EMBRYO.

HOMOLOGOUS FEATURES CAN RESULT FROM MODIFICATIONS THAT CHANGE AND ORIGINAL FEATURE TO TWO EXTREMELY DIFFERENT TYPES, SUCH AS A WING AND AN ARM. THE PRESENCE OF HOMOLOGOUS FEATURES IN DIFFERNT SPECIES INDICATES THAT THE SPECIES SHARED A FAIRLY RECENT COMMON ANCESTOR.

ANALOGOUS FEATURES SERVE IDENTICAL FUNCTIONS, AND THEY LOOK SOMEWHAT ALIKE, BUT THEY HAVE VERY DIFFERENT EMBRYOLOGICAL DEVELOPMENT, AND MAY BE VERY DIFFERENT IN INTERNAL ANATOMY.

THE WINGS OF BIRDS AND INSECTS ARE AN EXAMPLE OF ANALOGOUS FEATURES. ANOTHER EXAMPLE IS THE WINGS OF A HUMMINGBIRD AND HUMMING MOTH, BOTH ORGANISMS CAN HOVER TO FEED ON SUGAR RICH NECTAR FROM FLOWERS, BUT THERE IS NO ANATOMICAL OR EMBRYOLOGICAL SIMILARITY BETWEEN THE WINGS. WE CAN INFER THAT THEIR WINGS EVOLVED INDEPENDENTLY AND DIFFERENTLY IN MORE RECENT ANCESTORS OF EACH ANIMAL.

VESTIGIAL STRUCTURES: MANY ORGANISMS HAVE FEATURES THAT SEEM TO SERVE NO USEFUL FUNCTION. HUMANS HAVE A TAILBONE AT THE END OF THE SPINE THAT IS OF NO APPERENT USE. THE HUMAN APPENDIX ALSO HAS NO KNOWN FUNCTION. THESE APPARENTLY USELESS FEATURES ARE SAID TO BE VESTIGIAL.