Chapter 3 Outline
HEIRARCHY
- ATTRIBUTES OF LIVING ORGANISMS CAN BE ORGANIZED INTO A HEIRARCHY
- HIERARCHICAL DISTRIBUTION OF FEATURES IS THE MOST FUNDAMENTAL PROPERTY
OF THE BIOTA, I.E. ALL LIVING ORGANISMS THAT HAVE POPULATED THE EARTH
- e. g., all organisms possessing fur (mammals) are a subset
of all organisms with backbones (vertebrates) which are a subset
of all living organisms
- CHARACTERS
- ISOLATED OR ABSTRACTED CHARACTERISTIC OF AN ORGANISM
- CHARACTER ACQUIRES MEANING WHEN ITS DISTRIBUTION AMONG A SELECTED GROUP
OF ORGANISMS IS CONSIDERED
- e. g., possessiom of retractile claws is a characteristic of the
group Felidae (cats), including domesticated cats, bobcats,
lions, jaguars and extinct saber-toothed tigers
- POSITION IN THE HIERARCHIY IS OF GREAT SIGNIFICANCE
- e. g., possession of feathers is characteristic of all birds
and distinguishes birds from nonbirds; however, different birds
must be distiguished based on characters other than feathers
- GENERAL VS SPECIFIC CHARACTERS
- Specific characters characterize all members of a group
- General characters characterize a larger group
- e. g., possession of two eyes is a general character among humans
(and among all vertebrates) and cannot be used to distinguish different
humans, or for that matter a human from a frog; however, possession
of two eyes is a specific character for distinguishing vertebrates from
nonvertebrates
- CLADOGRAMS
- BRANCHING DIAGRAMS USED TO DEPICT THE HIERARCHICAL DISTRIBUTION OF
SHARED CHARACTERS
- USES OBSERVABLE FEATURES, NOT FUNCTIONS
- ARRANGEMENT OF CHARACTERS ON CLADOGRAM IS CONTROLLED BY CHOICE OF CHARACTERS
- CLADISTIC ANALYSIS HAS PROVEN TO BE A POWERFUL TOOL FOR STUDYING EVOLUTIONARY
RELATIONSHIPS AMONG ORGANISMS
ORGANIC EVOLUTION
- PHYLOGENY - HISTORY OF DESCENT OF ORGANISMS
- CLADES = MONOPHYLETIC GROUPS = NATURAL GROUPS
- GROUPS OF ORGANISMS IN WHICH MEMBERS OF EACH GROUP ARE MORE CLOSELY
RELATED TO EACH OTHER THAN TO ANY OTHER CREATURE
- MEMBERS SHARE A MORE RECENT COMMON ANCESTOR WITH EACH OTHER THAN WITH
ANY OTHER ORGANISM
- DESCENT WITH MODIFICATION
- MODERN ORGANISMS ARE EXTREMELY VARIED
- ANCIENT ORGANISMS HAVE VARIED THROUGH TIME
- LATER ORGANISMS HAVE DESCENDED & MODIFIED FROM EARLIER FORMS
- JEAN BAPTISTE DE LAMARCK
- 1ST ACCEPTED THEORY OF ORGANIC EVOLUTION INHERITANCE OF ACQUIRED
CHARACTERISTICS
- organism acquires traits during lifetime & passes them
on to descendants
- CHARLES DARWIN & ALFRED R. WALLACE
- PROVIDED THE KEY CONCEPT: EVOLUTION PROCEEDS THROUGH NATURAL SELECTION
("THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION"; 1859)
- 1. there is natural variation among the individuals of a given species
- 2. some variations are more favorable than other variations
- 3. organisms produce many offspring that die before maturity
- 4. individuals surviving to reproduce must be those with the most
successful combinations of variable characteristics
- EVIDENCE FOR ORGANIC EVOLUTION
- EMBRYOLOGY
- similarities early in development (tails in humans); divergence
in later stages
- COMPARATIVE ANATOMY
- homologous structures, e. g., tetrapod limbs modified to
wings or fins, as opposed to analogous structrures, e. g., bird/bat
wings vs. fly wings
- vestigial organs [non or partially funtional organs], e. g.,
horse toes & mammalian dewclaws, whale &
snake pelvises, human appendix & wisdom teeth
- BIOCHEMISTRY
- DNA, activator genes, ADP, blood proteins
- SMALL SCALE EVOLUTION
- industrial melanization
- insecticide/antibiotic resistance
- FOSSILS
- fossils are observed to change through time
- SIMPLEST & LEAST SIMILAR TO MODERN IN OLDEST ROCKS
- COMPLEX & MOST SIMILAR TO MODERN IN YOUNGER ROCKS
- HIERARCHICAL DISTRIBUTION OF CHARACTERS AMONG ORGANISMS
- CLADOGRAMS AND THE RECONSTRUCTION OF PHYLOGENY
- TREE OF LIFE = THE SINGLE PHYLOGENY THAT DOCUMENTS THE INTERRELATEDNESS
OF ALL LIFE
- CLADOGRAMS ARE USED TO DELINEATE BRANCHES ON THE TREE OF LIFE
- ORGANISMS THAT ARE CLOSELY RELATED SHARE SPECIFIC FEATURES
- Specific Characters = Derived (aka advanced)
- General characters = Ancestral (aka primitive)
- Only derived characters provide evidence of monophyletic groups
- PARSIMONY
- CLADOGRAMS ARE HYPOTHESES OF RELATIONSHIP
- WITH A GIVEN SET OF CHARACTERS, IT MAY BE POSSIBLE TO CONSTRUCT SEVERAL
POSSIBLE CLADOGRAMS
- DIFFERENT HYPOTHESES OF RELATEDNESS CAN BE DISTINGUISHED BY THE PRINCIPLE
OF PARSIMONY
- THE SIMPLEST CLADOGRAM, THE ONE WITH THE FEWEST EVOLUTIONARY EVENTS,
IS THE PREFERRED CLADOGRAM ACCORDING TO PARSIMONY
- SCIENCE & TESTING HYPOTHESES
- SCIENCE IS AN APPROACH TO CERTAIN KINDS OF ISSUES ROOTED IN A PARTICULAR
TYPE OF LOGIC
- AN HYPOTHESIS IS PROPOSED AND TESTED
- The hypothesis is rejected if it is falsified
- The hypothesis is never really proved - just not falsified
- CLADOGRAMS CAN BE TESTED BY ADDING CHARACTERS
- The cladogram is rejected if it is not the most parsimonious
- Robust cladograms have survived many falsification attempts