Question
• What is wrong with the following statement?:
• It is only a theory, so when evolution is taught, students should be
presented with other scientific alternatives
• What is Science?
Evolution of Evolution
• Was Darwin the author of the concepts of Evolution?
• Greek and Roman philosophers
• The French - late 1700’s
• Lamarck - inheritance of acquired characters
Evolution of Darwin
• Natural scientist - the third career choice
• H.M.S. Beagle
• The conservative approach
• Wallace
• 1859 - publishes On the Origin of Species by Means of Natural Selection
Paleontology's Role to the Study of Evolution
• Only paleontology can consider questions concerning the tempo and mode
of evolution
• exception: genetic clocks => controversial?
Darwinian Evolution
• Charles Darwin revolutionized biology with his theory of natural selection
• Darwinian evolution
• natural selection: (the mechanism) the individuals that are the most
fit (fitness) survive to reproduce to pass their genes along to the next generation.
• The great tautology of evolution: we measure fitness by looking at how
successful an individual is at reproduction. Some say this makes testing the
hypothesis of natural selection impossible.
Natural Selection
• Natural Selection; recognized by CD as the primary mechanism of evolution
• Over production of offspring by parents
• Variation within the offspring that is heritable (heritable variation);
Darwin couldn't explain this; was an empirical observation (no knowledge of
genetics yet)
Natural Selection
• Struggle for existence or survival for these offspring
• Those best adapted (the most fit) survive (survival of the fittest)
• The most fit pass on their traits to their offspring; etc.
• Darwin could recognize all this but didn't understand the mechanism;
how did heritability work?
• Mendel's work: particulate inheritance
Modern Synthesis - NeoDarwinism
• Natural Selection = one of the modes of evolution
• The reason natural selection works = genetics
• the particles = genes - which make up the molecule DNA (deoxyribonucleic
acid):
• sugar, phosphate, and nucleotide bases (the bases: adenine, thymine,
guanine, and cytosine)
• double helix structure of DNA: provides the replication mechanism --
the double helix unzips
• each 3 bases along the DNA form a gene; triplet code: codes for a particular
amino acid
Question
• What is the difference between Synapomorphies and Synpleisomorphies?
Hierarchy in Evolution
• Evolutionary changes can occur at a number of different levels: the
concept of evolutionary hierarchies
– differences between an individual, a population, and a species
• Goldschmidt's hierarchy: micro- and macroevolution
• 1. molecular evolution
• 2. individual level
• 3. evolution at the population level
• 4. species level (speciation)
• 5. changes between species (transpecific evolution): how higher level
clades are produced; how patterns through time are produced
• Where is the break between micro and macroevolution?
Hierarchy in Evolution
• Goldschmidt break: between 3. & 4.
• Wright break: between 4. & 5.
• microevolution covers the first 3 levels
• macroevolution covers the 5th level
• and species level kind of falls in between
• paleontologists refer to phyletic trends vs. phylogenetic
• trends (micro- vs. macroevolution respectively)
Evolution at the Microevolution Level
– the source of variation at each level
• Molecular evolution: at the Gene or DNA level
• source of variation:
o point mutations - chemical changes within the DNA; one nucleotide base substitutes
for another
• the ultimate source of variability; variability is the key to evolution
Evolution at the Individual Level
• during the production of gametes (process of meiosis) recombination
occurs: two alleles for each chromosome; prior to gametogenesis genes will swap
between alleles; another source of variability
• recombination to lead to chromosomal mutations
• during fertilization half the chromosomes come from each parent; sexual
recombination
Evolution at the Population level
• population: individuals of a species that interbreed; usually confined
to a geographic area
• gene flow between the individuals; adds variability
• genes can become fixed or lost within a population due to natural selection
• if population number is small, chance effects can become important:
genetic drift
• immigration and emigration changing gene pool: "founder effect”
• every thing in the first 3 levels is considered microevolution
Evolution at the Species Level
• Species level = most imprtant to paleontologists
• microevolutionary changes and processes not preserved in the fossil
record
• Types of processes:
• 1. phyletic shift or anagenesis -- slow, gradual genetic change within
a species through time
• one species gradually changes into the other
• no increase in diversity; number of species remains constant
• may be due to the fixation of genetic variability created at the microevolutionary
levels
• concept of a chronospecies: if lived at the same time wouldn't have
been able to interbreed
Evolution at the Species Level
ß 2. speciation or cladogenesis -- a splitting event see an increase in
diversity; diversification
ß Speciation Models
ß A) allopatric speciation: peripheral isolate; reproductively isolated
(usually geographically);independent genetic change; populations reunited
Evolution at the Species Level
B) quantum speciation: see rapid changes in morphology during a speciation event
- what might cause this? "bottlenecking"; small isolates;
- may happen sympatrically with regulatory gene mutations
- also includes heterochrony
Rates of Speciation
phyletic gradualism vs. punctuated equilibrium:
phyletic grad.: after speciation most evolutionary change occurs via anagenesis
punct. equil.: most evolutionary change occurs through speciation; very little
change very little change between speciation events (stasis); speciation occurs
in peripheral populations
-there's fossil evidence to suggest both can occurMacroevolution: Transpecific
Evolution
• how do we get patterns of diversification through time? how are clades
formed (higher taxa)?
• new groups of species (artificially grouped by into higher taxonomic
levels) that have different body plans (and therefore have different life modes)
that radiate; how and why does this happen?
• these are processes that occur at transpecific levels; after species
are already created
Question
• What is the difference between micro- and macroevolution?Macroevolution:
Transpecific
Evolution
• Controversy
• Micro- versus macroevolutionists
• Modern Synthesis school:
• transpecific level changes = accumulation of changes from lower levels
• Processes = identical
• Population changes - species originate
• Species accumulate - transpecific trends occurMacroevolution: Transpecific
Evolution
• Hierarchical Model school:
• different processes operate - micro- vs. macroevolutionary levels
• discontinuity - between species level and the transpecific level
• discontinuity in process - micro - vs. macroevolution
– Wright Break
Hierarchical Model
• transpecific level processes
• Species Selection
• analogous to natural selection
• Species - individuals; speciation - variation; extinctions - death
• species selection - survival - species -> speciation
Hierarchical Model
• Clades or trends - created one of two ways:
• Rapid speciation (species or group) = more descendent species
• Prone to extinction - if morphologically skewed - trend may develop
• The existence of species selection = highly controversial
Where has Diversification Taken Place?
• Onshore-Offshore Expansion Model - Sepkoski and Sheehan, 1983
• consider the Ordovician radiation (where Paleozoic fauna took over)
• new species originate onshore and with time migrate offshore while displacing
existing species
• The evidence
• Problems with the analysis?
• Their reasoning:
- nearshore environments frequently disturbed
- might expect to get small peripheral isolates in nearshore
- environments where allopatric speciation might occur more frequently
provocative