Chapter 18
CLASSIFICATION
I. History of Taxonomy
J.
Definition: Taxonomy is the branch of Biology that names and groups organisms according to
their characteristics and evolutionary history.
K. Early systems of Classification
1. Aristotle a. Greek Philosopher
b. Classified animals into three groups (Air dwellers, land dwellers, and water dwellers)
c. Scientists realized that Aristotle's system was NOT adequate (Ducks live on land, in
water, fly in the air)
2. Problem with common names a. vary ftom one locale to another (Irish elk is our moose)
b. descriptions are not accurate (for instance, jellyfish)
c. Solution - use Latin as the universal language for Biologists (Greek is also used!)
1) Latin is not changing today (not used by any major people's, so isn't picking up
slang words, or being modified) examples: cool, groovy, tubular
2) Is descriptive (for example, flower color - aurum = gold color, from aura, or gold;
cerum = pink)
C. Carolus Linnaeus
1. Swedish Naturalist who devised our current taxonomic system
2.Used the morphology (Greek, meaning structure, or form) of the organism to classify it 3.
Seven hierarchical categories
D. Levels of Classification
1. KINGDOM - Largest of the seven levels; contains a LARGE NUMBER of organisms,
loosely related
2. PHYLUM - a subset of the Animal Kingdom, or DIVISION - a subset of the Plant
Kingdom (a group of closely related Classes)
3. CLASS - a subset of a PHYLUM (or DIVISION); a group of closely related Orders
4. ORDER - a subset of a Class (a group of closely related Families)
5. FAMIL Y - a subset of an Order ("
Genera)
6. GENUS - a subset of a Family ("
Species)
7. SPECIES - a subset of a Genus
8. SUBSPECIES (animal Kingdom) OR VARIETY (Plant Kingdom) - variations of a
species that occur in different geographic areas (example E. BINOMIAL NOMENCLATURE - means "two-word naming"
F. Modem Taxonomists rely on four criteria when classifying organisms
1. Morphological (structural) similarities
2. Cellular organization
3. Biochemical similarities
4. Phylogenic (genetic, or evolutionary) similarities
IT.
MODERN PHYLOGENETIC TAXONOMY
A. SYSTEMATIC TAXONOMY (Systematics, for short) - organizes living things in the
context of evolution.
1. Phylogenetic Tree - a family tree that shows the evolutionary relationships thought to
exist among groups of organisms.
a. represents a hypothesis
b. based on several lines of evidence, including
1) morphology
2) Patterns of embryological development (example - gills slits are characteristic of
chordates, including humans)
3) Biochemical similarities, such as chromosomal characteristics (DNA nucleotide
sequencing; amino acid sequencing in proteins)
c. is subject to change as new information arises
B. THE FOSSIL RECORD
L Provides clues to evolutionary relationships
2. Is incomplete, and therefore is confirmed with other lines of evidence
C. MORPHOLOGY
D. Homologous features - features which have the same (embryonic and evolutionary) origin;
they may have diverged in their function and phenotypic appearance, but their relationships
to adjacent structures and embryonic development are basically the same. examples
include: seal's front flipper; bat's wing; cat's paw; horse's front leg; human hand and arm;
indicates species share a fairly recent common ancestor
2. Analogous features - features which are similar in function (and often in superficial
appearance) but which are of different evolutionary origin; examples include wigs of a
robin, and the wings of a butterfly; legs of a crawdad and the legs of a human; both for the
same purpose, but evolved from different ancestral structures
D. VESTIGIAL STRUCTURES - structures which were useful to an ancestor, but not to the
modern organism that has them.
E. a vestigial structure is evidence that the structure was functional in some ancestor of the
modern organism
2. provides evolutionary clues, as in the whale (ancestor probably lived on land)
3. other examples include: human appendix, tailbone, and wisdom teeth; functionless eyes of
cave-dwelling animals;
E. EMBRYOLOGICAL PATTERNS OF DEVELOPMENT
1. All vertebrate embryos are similar in the early stages of their development (see pg. 291)
2. Indicates that vertebrates share a common ancestor
3. Zygote -> Blastula -> Blastopore
a. Blastopore becomes anterior end of digestive system in most animal phyla
b. Blastopore becomes posterior end of digestive system in chordates! (See diagram on
pg.343 )
F. MACROMOLECULES AND CHROMOSOMES
1. Taxonomists compare macromolecules for homologous protein molecules in different
species
a. Examples of macromolecules include RNA, DNA, and proteins
b. serve as "molecular clocks" (number of amino acid differences related to the point in
time when two species diverged from a common evolutionary ancestor)
c. example: human vs. gorilla hemoglobin differ by only one amino acid; human vs.
frog differs by 67 amino acids! Closer similarity implies closer ancestry or
relatedness
;~
2. compare karyotypes (patterns) of chromosomes of two related species
(see fig. 18-5, pg 345)
a. regions of chromosomes with same banding patterns are compared
b.Closer similarity implies closer ancestry or relatedness c.
example: humans and chimpanzees
3. both macromolecules and chromosomes are used to show "degree of relatedness"
between species
III.
IV.
CLADISTICS
A. definition: a system of phylogenetic classification which utilizes shared derived
characteristics to establish evolutionary relationships
- 1. Derived character - a feature that evolved only within the group under consideration _ a. example
- feathers; since birds are the only animals with feathers, it is logical to assume that feathers evolved
within the bird group and were NOT inherited from some distant ancestor of birds.
b. Organisms which share a derived character such as feathers logically inherited it trom
a common ancestor.
2. the more derived characters a group shares, the stronger the evidence of common
ancestry between organisms that share them.
_ B. Cladogram - An ancestry diagram made by means of cladistic analysis (see pg.346)
MODERN SYSTEMS OF CLASSIFICATION
A. Six Kingdom System - (See table 18-2,.p 347)
1. Kingdom Archaebacteria
a. Unicellular prokaryotes
b. Distinctive cell membranes
c. Unique biochemical and genetic properties (compared to other life on earth)
d. Many tolerate harsh environments, including hot temperatures, anaerobic
environments
e. Several are chemosynthetic
f. Evolved before oxygen released through photosynthesis g.
Archae - is Greek for "ancient"
2. Kingdom Eubacteria
a. Eu - means "true"
b. Unicellular prokaryotes
c. Most bacteria: you are familiar with today
d. Most are aerobic (use oxygen)
e.Have ability to undergo genetic recombination f.
Short generation time
f. These (e & t) allow for genetic diversity, and rapid evolutionary response; this is true
of Archaebacteria as well!
3. Kingdom Protista
a. primarily single celled eukaryotes, but some multicellular
b.contains all eukaryotes that are not plants, animals, or fungi (~50,000 species) c.
examples include Euglena and Amoeba
4. Kingdom Fungi
a. comprised of heterotrophic unicellular and multicellular eukaryotic organisms
b. demonstrate genetic recombination
c. > 100,000 species
d. examples include mushrooms, molds, smuts, rusts, and mildews
5. Kingdom Plantae
a. consists of multicellular plants
b. most are autotrophic and photosynthetic
c. have a sexual cycle based on meiosis
d. > 350,000 species
e. examples include mosses, ferns, conifers, and flowering plants
6. Kingdom Animalia
a. eukaryotic, multicellular heterotrophic organisms
b. most exhibit some type of symmetry
c. most have a sexual cycle that employs meiosis
d. examples include (instructor's choice! ©)
B. Three Domain System
.
1. Based on sequences of ribosomal RNA
2. Phylogenetic tree based on RNA studies shows three natural broad groups, called
Domains
a. Domain Archaea (the Archaebacteria)
b. Domain Bacteria (the Eubacteria)
c. Domain Eukarya (all the rest - protists, fungi, plants, and animals
d. Most variation is among the protists! Others are actually quite similar to each
other!