1. Evidence for Evolution
Part 1

2. Selective breeding of domesticated animals
Dog breeds bred from ancestors of the modern wolf
Selected for physical traits (size, color, fur type, etc.)
Also behavioral traits (loyalty, intelligence, hunting…)
Selective breeding – only those individuals with desired combinations of alleles are allowed to reproduce. AKA: Artificial Selection

3. Examples of selective breeding: Seen in pets, crops, etc.
Animals
Plants

5. Homologous anatomical features
Have same origin, so work with the same building blocks
Building blocks are modified to different purposes in different species, but ancestry is evident

6. Pentadactyl Limb

7. Homology in Vertebrate Embryology
In vertebrates, gill slits and post-anal tail modified as embryonic development proceeds.

8. Homology in Vestigial features
Features that had a function in an ancestor, but no longer serve a function
Ex. Tiny leg bones in some whales
Ex. Embryonic teeth in chickens

9. Homologous versus Analagous features
From different origins, so different building blocks
Similar function selects for similar traits
Hydrodynamic: dorso-ventral flexion v. side-to-side

10. Placentals and Marsupials
Marsupials evolved first
Continents were one large land mass
After Australia split away, placental mammals evolved on the major land mass
In most cases, placentals outcompeted marsupials
A few generalized species exist in the Americas (ie. Possums), but the vast diversity is in Australia

11. Mammals
Placentals and marsupials are fundamentally different in structure
However, in a large ecosystem with similar niches, similar traits are helpful
Similar features are seen in animals with similar niches

12. Homologous or Analogous?
As front limb: homologous
As flying limb: analogous

13. Why homology and analogy?
Convergent evolution
In similar situations, organisms with similar roles have similar needs
Cactus Euphorbia
Divergent evolution
In similar species with different roles different variations will be helpful
Alpaca Camel (bactrain)
Leaves

14. Observed Evolution
Finches have diversified on the isolated Galapagos Islands to form different species

15. Finch beaks Selective pressure seen in years of drought
Beak size changes in a single species (deeper)
Beak size is heritable
Finch beaks

16. Antibiotic resistance
The first mass-produced antibiotics were used in 1944
Staphylococcus aureus (a bacteria that can be harmless or cause deadly infections) first showed resistance (weak) in 1947

17. MRSA
Methicillin-resistant Staph. a. infections (MRSA) were originally found only in hospitals
Now they are found in communities and attack otherwise healthy athletes, children, etc.

18. How does resistance evolve?
Mutations (most useless or worse)
Natural Selection
Speeded up by swapping of DNA between bacteria

19. What are fossils? Traces of living things
Pertified, casts / mould, ice, amber, tar, etc.

20. Fossil evidence for evolution
Paleontological findings:
Fossils exist in ancient strata, dated into the billions of years.
Many fossils are different than anything living currently
Fossils are different in different strata, and follow in a reliable sequence of orderly change
There are “transitional” fossils that have intermediate characteristics between major groups (such as reptile to mammal)

21. Fossil evidence for evolution
Whale evolution (as seen in PBS: Great Transformations!)
1. Primitive Whales (e.g.: Dorudon, Prozeuglodon) ~ 36 mya
2. (1990) Basilosaurus isis (hind leg found) ~ 37 mya
3. (1994) Rodhocetus kasrani ~ 46 mya
4. (1994) Ambulocetus natans ~ 48 mya
5. (1983) Pakicetus inachus (skull and teeth only) ~ 50 mya
6. Mesonychids (extinct land mammals, with whale-like teeth, e.g. Pachyaena, Sinonyx,) ~ 55 mya (or Arteriodactyls??) 4 1 5 2 6 3

22. Further fossils
Archaeopteryx
Teeth, claws, feathers

23. Further fossils Acanthostega
4 legs, gills, fish-like tail, 8 fingers / 7 toes

24. Finding the age of fossils
Relative dating – determining ages in comparison to other samples (older / younger)
Absolute dating – determining ages in years
Radiometric dating – measures the amount of radioactive isotope in a sample
14C: half-life 5,730 years, used for fossils 1,000 – 100,000 years old
40K: half-life 1,250 million years, used for fossils >100,000 years old*

25. Finding the age of fossils
Radioactive isotopes are unstable; they decay into other isotopes.
The pattern of decay is always the same, but the amount of time it takes varies
The amount of time for half the atoms to decay is the half-life

26. Radiometric dating
Given the length of the half-life, and the amount of radioisotope remaining, the age of the fossil can be determined

27. Details for Carbon / Potassium
40K is locked in new rocks
Decay product is 40Ar (argon gas – would leave rock if not trapped)
Grinding sample frees 40Ar, age can be estimated
14C continually produced in atmosphere, oxidized to (14)CO2, also breaking down
14CO2 taken up by plants
Organisms keep a constant level of 14C while alive by interactions with ecosystem (photosynthesis / eating / respiration)
Once dead, 14C begins to decrease since no more exchange with environment

28. Radiometric dating
If the age is between half-lives, use the formula t = X (ln(1 + D/P) /.69)
where X = half-life and D/P is the ratio of decayed atoms to parental (radioactive) atoms
What is the age of the sample if:
25% of 14C remains?
25% of 40K remains?
87.5% of 14C has decayed?
67% of 40K remains?
11,460 years old
2.5 billion years old
17,190 years old
730 million years old

29. Next Unit: DNA / protein sequences
Show relatedness of all species
More distant relations show increasing differences in DNA / protein
Can be used to make “family tree” of life