INTRODUCTION
Updated 9 Jan 09
THEORY OF EVOLUTION (pp. 8-25)
Evolutionary theory is the basis for today’s classification system
Charles Darwin was the first to formalize the ideals that we know as the Theory of Evolution
What is a theory?
1) start with observations
2) use that to develop a hypothesis (educated guess on what will happen
3) use scientific method (experimentation, gather data) to test your hypothesis
4) repeated experimentation can lead to generalizations  a theory
Darwin’s theory of evolution is thought by many as a set of five theories:
1. Perpetual Change – a species changes from generation to generation through genetic
modification (individuals don’t change, species do).
2. Common Descent – as we follow individual back through generation we find that many
have a common ancestor.
3. Multiplication of species – new species develop as a result of modification of older species
that become reproductively isolated.
4. Gradualism – large difference between organisms is the result of incremental changes over
long periods of time.
5. Natural Selection – each species adapts to the environment in which it lives.
CLASSIFICATION SYSTEM
All organisms classified by the extent of genetic similarities
Evidence based on:
1) morphology (overall shame and structure)
2) anatomy (internal structure)
3) biochemistry (molecular production)
4) cytology, including DNA & RNA structure (chromosomes, nucleotide sequence)
Introduction, pg. 2
CLASSIFICATION: THE DOMAINS
Domain Bacteria (typical bacteria)
prokaryotic: no membrane bound organelles
noncoding DNA segments absent (all used)
cell wall with sugar-amino acid combination
wide variety of habitats
Domain Archaea (methanogens & halophiles)
prokaryotic: no membrane bound organelles
some noncoding DNA segments present (introns)
cell wall of polysaccharide only
only in extreme habitats
Domain Eukarya (protistans, plants, fungi, animals)
eukaryotic: membrane bound organelles present
many noncoding DNA segments present
cell wall of polysaccharide or absent
in most habitats
CLASSIFICATION: KINGDOMS (pp. 84-85)
Historically Zoology has incorporated two historical Phyla within Domain Eukarya
Kingdom Animalia
multicellular with cell specialization
no cell wall
no chloroplasts (chemosynthetic)
Kingdom Protista
unicellular or multicellular with little cell specialization
cell wall present or absent
chloroplasts present (photosynthetic) or absent (chemosynthetic)
Only a part of this second group fits into Zoology – the "protozoa"
Protista have been subdivided into several different phyla (phylogeny is still under revision)
Introduction, pg. 3
LOWER LEVELS OF CLASSIFICATION
Phylum (Division for photosynthetic organisms)
Class  Order  Family  Genus  Species
Each may be defined by the levels above or below:
A Class is a group of related Orders
A Class is a portion of a Kingdom
Classification scheme recognized at several levels:
lowest level is least inclusive = SPECIES
DEFINITIONS OF SPECIES: (pp. 75-76)
1) Biological definition: a reproductive group of populations that occupies a specific niche in
nature
[all organisms which have potential to reproduce together]
Advantage: views a species based on reproductive process, a basic definition of live
Problem: had to determine reproductive ability and ignores asexual forms
2) Evolutionary definition: a single lineage of ancestor-descendant populations that maintains its
identity from other lineages and has its own historical fate
[all individuals that have a common ancestor that tend to group similar populations
together]
Advantage: puts similar groups together and does not require a reproductive knowledge
Problem: some individual and isolated populations may actually be distinct species
3) Phylogenetic definition: an irreducible grouping of organisms diagnosably distinct from other
such groupings and within which there is a parental pattern of ancestry and descent
[all individuals that can be grouped by descendance and emphasizes smaller groupings]
Advantage: liked by conservation biologists in conserving all unique life forms
Problem: tends to overly split groups into distinct species
The traditional naming of a species includes use of two words:
generic epithet (in CAPS) and specific epithet (lc)
Homo sapiens (humans)
Anolis carolinensis (green anole)
Introduction, pg. 4
PHYLOGENY (pp. 76-84)
The evolutionary history of origin and diversification of a group of organisms
In studying phylogeny we look for:
1) which species had common ancestors
2) what features did they have common - homology
These ideas are implied with terms like insects, mammals
The results of the thought process typically can be represented in a branched system of a cladogram
(a "tree")
Cladograms have been based on many features:
morphology & anatomy
biochemistry
chromosome number and size
Chromosome structure, including nucleotide sequence
Compared to actual evolutionary relationships, a cladogram maybe (fig 4.5, p. 79):
1) monophyletic = correct
2) paraphyletic = include all of a group + some others too
2) polyphyletic = include some from several groups
A big problem with classification of Kingdom Protista:
the group is clearly polyphyletic
ORGANISMAL LIFE CYCLES
Typically organisms alternate between haploid and diploid forms
we are most familiar with the diploid form
these terms refer to the number of sets of chromosomes
haploid = 1 set (1n)
diploid = 2 sets (2n)
most body cells of humans are diploid
the reproductive cells (egg & sperm) are haploid
Continuation of life from one generation to another is based on reproductive processes
Mitosis = production of identical cells of same chromosome #
Meiosis = production of homologous cells, half chromosome #
Introduction, pg. 5
MITOSIS
maintain chromosome #
2n  2n or
1n  1n
for organism growth & asexual
reproduction
produces more of same cell type
Life cycle:
MEIOSIS
reduction in chromosome #
2n  1n
for sexual reproduction
produces reproductive cells
Introduction, pg. 6
LEVELS OF COMPLEXITY
Cell Theory = ideal that the cell is central to life
1) cell is the smallest living unit
2) all organisms are made of one or more cells
3) all cells come from preexisting cells
Various levels of organization above the cell:
tissue  organ  organ system  organism
As we look at the diversity of animals in this course, there is much variation in complexity:
* some unicellular organisms (paramecium)
* some organisms only of tissues (sponges)
* some organisms with cells, tissues & organs (flatworms)