Evolution Evidence and Speciation Fossils Preserved remains of living things Paleontology is the...
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Transcript of Evolution Evidence and Speciation Fossils Preserved remains of living things Paleontology is the...
Fossils
Preserved remains of living things Paleontology is the study of the fossil
record Most organisms do not leave a fossil after
death Explains the “missing links”
Sedimentation Fossils As the organism decomposes the spaces will be
filled with the minerals from the silt
Evidence for Evolution
How old is that fossil?
Relative Dating Age of fossils based according to their location
in strata
Absolute Dating Age of fossils determined by analyzing the
content of radioactive isotopes found in the fossil.Half-life: The length of time required for half of the
radioactive elements to change into another stable element.
Unaffected by temperature, light, pressure, etc.All radioactive isotopes have a dependable half life.
Ex: C14 decays into N14
How radioactive “naturally occurring”
elements get inside an organism:
A.K.A – Radiometric
dating
Absolute Dating
Evidence for Evolution HOMOLOGY is a characteristic shared by
two species (or other taxa) that is similar because of common ancestry.
Types of homology
morphological homology – species placed in the same taxonomic category show anatomical similarities.
ontogenetic homology - species placed in the same taxonomic category show developmental (embryological) similarities.
molecular homology - species placed in the same taxonomic category show similarities in DNA and RNA.
MORPHOLOGICAL HOMOLOGY
Structures derived from a common ancestral structure are called:
HOMOLOGOUS STRUCTURES
Ontogenetic Homology The human embryo has gills, a post-anal tail,
webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water
Evidence for Evolution
MORPHOLOGICAL HOMOLOGY A structure that serves the same function in
two taxa, but is NOT derived from a common ancestral structure is said to be an
ANALOGOUS STRUCTURE
Sugarglider
AUSTRALIA
NORTHAMERICA
Flyingsquirrel
•Some similar mammals that have adapted to similar environments
–Have evolved independently from different ancestors
Vestigial Structures
Have marginal, if any use to the organisms in which they occur.
EXAMPLES: femurs in pythonid snakes and pelvis in
cetaceans (whales) appendix in humans coccyx in great apes
Evidence for Evolution
Vestigial organs
Why would whaleshave pelvis & leg bones
if they were alwayssea creatures?
These areremnants of
structures that were
functional inancestral species
Evolution evidence at the cellular level Domains: Archaea, Bacteria and Eukarya
Elements conserved through all: DNA, RNA and many metabolic pathways.
Eukaryotes – core features: Cytoskeleton Nucleus Membrane-bound organelles Linear chromosomes Endomembrane system
So…what is a species?
• Population whose members can interbreed & produce viable, fertile offspring
• Reproductively compatible
Western Meadowlark
Eastern Meadowlark
Distinct species:songs & behaviors are different enough to prevent interbreeding
Correlation of speciation to food sources
Adaptive radiation
Seedeaters
Flowereaters
Insecteaters
Rapid speciation:new species filling niches,
because they inheritedsuccessful adaptations.
How do new species originate?
When two populations become reproductively isolated from each other.
Speciation Modes: allopatric
geographic separation “other country”
sympatric still live in same area “same country”
Allopatric Speciation
Physical/geographical separation of two populations
Allele frequencies diverge After a length of time the
two population are so different that they are considered different species
If the barrier is removed interbreeding will still not occur due to pre/post zygotic isolation
Sympatric Speciation
Formation of a new species without geographic isolation. Causes:
Pre-zygotic barriers exist to mating Polyploidy (only organism with an even number of
chromosomes are fertile…speciation occurs quickly) Hybridization: two different forms of a species
mate in common ground (hybrid zone) and produce offspring with greater genetic diversity than the parents….eventually the hybrid diverges from both sets of parents
Gene flow has been reduced between flies that feed on different food varieties, even though they both
live in the same geographic area.
Sympatric Speciation
Pre-zygotic IsolationSperm never gets a chance to meet eggGeographic isolation: barriers prevent matingEcological isolation: different habitats in same regionTemporal isolation: different populations are fertile at different timesBehavior Isolation: they don’t recognize each other or the mating ritualsMechanical isolation: morphological differencesGamete Isolation: Sperm and egg do not recognize each other
PRE-Zygotic barriers
Obstacle to mating or to fertilization if mating occurs
behavioral isolation
geographic isolation ecological isolation temporal isolation
mechanical isolation gametic isolation
Post Zygotic Isolation
Hybrid Inviability – the embryo cannot develop inside the mothers womb
Hybrid Sterility – Adult individuals can be produced BUT they are not fertile
Hybrid Breakdown – each successive generation has less fertility than the parental generation
Patterns of Evolution• Divergent Evolution (adaptive radiation)• Convergent Evolution
– Two or more species that share a common environment but not a common ancestor evolve to be similar
Is it a shark or a dolphin??
Coevolution
Two or more species reciprocally affect each other’s evolution predator-prey
disease & host competitive species mutualism
pollinators & flowers
Evolutionary Time Scale
Microevolution – changing of allele frequencies in a population over time.
Macroevolution – patterns of change over geologic time. Determines phylogeny Gradualism – species
are always slowly evolving
Punctuated equilibrium – periods of massive evolution followed by periods with little to no evolution
Mass Extinctions
• At least 5 mass extinctions have occurred throughout history.
• Possible causes: dramatic climate changes occurring after meteorite collisions and/or continents drift into new and different configurations.
The Primitive Earth
Atmosphere: All chemicals/compounds necessary are thought
to have originated on earth Inorganic precursors:
Water vapor Nitrogen Carbon dioxide Small amounts of hydrogen and carbon monoxide
These were the monomers for forming more complex molecules.
Experiments have shown that it is possible to form organic from inorganic.
Water vapor
Condensed liquid with complex, organicmolecules
CondenserMixture of gases("primitiveatmosphere")
Heated water("ocean")
Electrodes discharge
sparks(lightning
simulation)
Water
Origin of Organic Molecules Abiotic synthesis
1920 - Oparin first molecules
formed by strong energy sources
1953 - Miller & Urey test hypothesis formed organic compounds
amino acids adenine
CH4
NH3
H2
Key Events in Origin of Life
Origin of Cells (Protobionts) lipid bubbles separate inside from outside
metabolism & reproduction Origin of Genetics
RNA is likely first genetic material multiple functions: encodes information (self-
replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA) makes inheritance possible makes natural selection & evolution possible
Origin of Eukaryotes endosymbiosis
Timeline
Key events in evolutionary history of life on Earth 3.5–4.0 bya:
life originated 2.7 bya:
free O2 = photosynthetic bacteria
2 bya:first eukaryotes
First Eukaryotes
Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency
natural selection!
infolding of theplasma membrane
DNA
cell wall
plasmamembrane
Prokaryoticcell
Prokaryotic ancestor
of eukaryotic
cells
Eukaryoticcell
endoplasmicreticulum (ER)
nuclear envelope
nucleus
plasma membrane
~2 bya
1st Endosymbiosis
Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but
did not digest them mutually beneficial relationship
natural selection!
Ancestral eukaryotic cell
Eukaryotic cellwith mitochondrion
internal membrane system
aerobic bacterium mitochondrion
Endosymbiosis
mitochondrion
chloroplast
Eukaryotic cell withchloroplast & mitochondrion
Endosymbiosis
photosyntheticbacterium
2nd Endosymbiosis
Evolution of eukaryotes origin of chloroplasts engulfed photosynthetic bacteria,
but did not digest them mutually beneficial relationship
natural selection!
Eukaryoticcell with
mitochondrion
Theory of Endosymbiosis
Evidence structural
mitochondria & chloroplasts resemble bacterial structure
genetic mitochondria & chloroplasts
have their own circular DNA, like bacteria functional
mitochondria & chloroplasts move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell
Lynn Margulis