1. Evolution Evidence and Speciation

2. Evidence for Evolution 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

3. How old is that fossil? Relative Dating Absolute 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

4. Relative Dating

5. How radioactive “naturally occurring” elements get inside an organism:
Absolute Dating
How radioactive “naturally occurring” elements get inside an organism:
A.K.A – Radiometric dating

6. Evidence for Evolution
HOMOLOGY is a characteristic shared by two species (or other taxa) that is similar because of common ancestry.

7. 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.

8. MORPHOLOGICAL HOMOLOGY
Structures derived from a common ancestral structure are called:
HOMOLOGOUS STRUCTURES

11. Evidence for Evolution
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

13. Figure 22.15
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo

14. 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

16. Some similar mammals that have adapted to similar environments
Have evolved independently from different ancestors
Sugar
glider
AUSTRALIA
NORTH
AMERICA
Flying
squirrel

17. Evidence for Evolution
Molecular Homology

18. Evidence for Evolution
                                                                                                                                                                           

19. Evidence for Evolution

20. Evidence for Evolution
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

21. Vestigial organs
These are remnants of structures that were functional in ancestral species
Why would whales have pelvis & leg bones if they were always sea creatures?
Remains of ancestral structures = mutations can occur without affecting survival & reproduction
Evolutionary relationship
snakes & whales — remains of pelvis & leg bones of walking ancestors
eyes on blind cave fish
human tail bone

22. 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

23. There’s something you need to know…
The Origin of Species
Mom, Dad…
There’s something you need to know…
I’m a MAMMAL!

24. Reproductively compatible
So…what is a species?
Population whose members can interbreed & produce viable, fertile offspring
Reproductively compatible
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark 24

25. Correlation of speciation to food sources
Seed eaters
Flower eaters
Insect eaters
Rapid speciation: new species filling niches, because they inherited successful adaptations.
Adaptive radiation

26. 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”

27. 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

28. 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

29. Sympatric Speciation
Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

30. Pre-zygotic Isolation
Sperm never gets a chance to meet egg
Geographic isolation: barriers prevent mating
Ecological isolation: different habitats in same region
Temporal isolation: different populations are fertile at different times
Behavior Isolation: they don’t recognize each other or the mating rituals
Mechanical isolation: morphological differences
Gamete Isolation: Sperm and egg do not recognize each other
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

31. PRE-Zygotic barriers
Obstacle to mating or to fertilization if mating occurs
geographic isolation
ecological isolation
temporal isolation
behavioral isolation
mechanical isolation
gametic isolation

32. 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
Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.
Even if hybrids are vigorous they may be sterile; chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Horse(64) x donkey(62) = mule (63 chromosomes)
In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.
On path to separate species.

33. 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??

34. Coevolution
Two or more species reciprocally affect each other’s evolution
predator-prey
disease & host
competitive species
mutualism
pollinators & flowers

35. 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

36. Rate of Evolution
Gradual evolution Punctuated evolution

38. 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.

40. What must Earth have been like before living things took over?
Origin of the Earth
What must Earth have been like before living things took over?

41. 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.

42. Origin of Organic Molecules
Water vapor
Condensed liquid with complex, organic
molecules
Condenser
Mixture of gases
("primitive
atmosphere")
Heated water
("ocean")
Electrodes discharge sparks
(lightning simulation)
Water
Abiotic synthesis
Oparin
first molecules formed by strong energy sources
Miller & Urey test hypothesis
formed organic compounds
amino acids
adenine
CH4 H2
NH3
Attempted to prove that chemical evolution could occur
The experiment
Used water, methane, ammonia, hydrogen sealed inside a glass container
Water was heated to produce steam and sparks were generated from electrodes
Water was then cooled and allowed to condense\
Experiment went on in this cycle for 1 week
Results
15% of carbon was now present in the form of organic materials
13 out of 20 amino acids were present
High concentrations of the base Adenine were also detected

43. 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
Life is defined partly by two properties: accurate replication and metabolism. Neither property can exist without the other. Self–replicating molecules and a metabolism–like source of the building blocks must have appeared together. How did that happen?
The necessary conditions for life may have been met by protobionts, aggregates of abiotically produced molecules surrounded by a membrane or membrane–like structure. Protobionts exhibit some of the properties associated with life, including simple reproduction and metabolism, as well as the maintenance of an internal chemical environment different from that of their surroundings.
Laboratory experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds. For example, small membrane–bounded droplets called liposomes can form when lipids or other organic molecules are added to water.

44. 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

45. Prokaryotic ancestor of eukaryotic cells
First Eukaryotes
~2 bya
Development of internal membranes
create internal micro-environments
advantage: specialization = increase efficiency
natural selection!
nuclear envelope
endoplasmic reticulum (ER)
plasma
membrane
infolding of the plasma membrane
nucleus
DNA
cell wall
plasma
membrane
Prokaryotic
cell
Prokaryotic ancestor of eukaryotic cells
Eukaryotic
cell

46. internal membrane system
1st Endosymbiosis
Evolution of eukaryotes
origin of mitochondria
engulfed aerobic bacteria, but did not digest them
mutually beneficial relationship
natural selection!
internal membrane system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion

47. photosynthetic bacterium chloroplast & mitochondrion
2nd Endosymbiosis
Eukaryotic
cell with
mitochondrion
Evolution of eukaryotes
origin of chloroplasts
engulfed photosynthetic bacteria, but did not digest them
mutually beneficial relationship
natural selection!
photosynthetic bacterium
chloroplast
mitochondrion
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion

48. Theory of Endosymbiosis
Lynn Margulis
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

49. Cambrian explosion Diversification of Animals
within 10–20 million years most of the major phyla of animals appear in fossil record
543 mya