2. Natural Selection It is a two step process:
The unequal survival and reproduction of organisms due to environmental forces, resulting in the preservation of favorable adaptations.
It is a two step process:
1. The production of variation in a population
2. Non-random aspects of survival and reproduction

3. Natural Selection is a two step process:
Step One: The Production of Variation. (Chance)
Mutations
Meiosis:
recombination due to crossing-over in 1st division
random movement of chromosomes in 2nd division
Random mate selection & fertilization
Step Two: Non-random aspects of survival and reproduction
Superior success of certain phenotypes
Nonrandom mate choice

4. Lemurs of Madagascar

5. Amazonian Frogs

6. Humans select traits for dogs, pigeons and other animals when they breed them.
Bred Pigeons came from a single original species
Who selects the traits for wild plans & animals?

7. Natural Selection is Survival of the fittest
NOBODY!!
There is no agent involved in natural selection.
Natural selection is a process of elimination
INDIVIDUALS THAT HAVE TRAITS THAT ARE BEST ADAPTED FOR THE CURRENT ENVIRONMENT ARE THE ONES THAT SURVIVE TO BREED AND PASS ON THEIR GENES TO THE NEXT GENERATION.
Organisms not possessing the beneficial traits either die or don’t have as many offspring.
Natural Selection is Survival of the fittest

8. Natural Selection is a mixture of both Chance and necessity
Natural Selection is not goal directed. It does not have a long term goal.

9. What acts as a selection pressure on a population?
Competition for food
Competition for a mate
Changes in the environment
Predators
Parasites
Example of Natural Selection in Action: Monarch / milkweed
Card game
Video of Darwin’s Finches

10. Main Types of Selection Pressures
Directional Selection
Natural selection favors one extreme of the population for that trait
often happens when environment changes in a consistent way- e.g.climate gets colder.
Disruptive Selection
Natural selection favors both extremes selected
Causes species to diverge
Stabilizing Selection
Natural selection favors the average for population selected
Sexual Selection

11. Directional Selection
Neck of Giraffe
Antibiotic resistance of bacteria
Moth color (melanin)
Camouflage/Mimics
Many sexually selected traits

12. Directional Selection: Mimicry (mimic environment)

13. Stabilizing Selection
When the extremes of the trait aren’t as well suited
Examples
bird clutch size
Elk Antlers size
Giraffe neck length
Tail length in birds

14. Disruptive Selection Causes divergence within the species
Occurs when two different types of resources in one area
Results in specialization for each branched group
May lead to formation of new species
E.g. Darwin’s Finches

16. Examples of selection pressures...
Predators - variants with adaptations allowing them to escape predators have more offspring
- e.g. speed, defensive weapons, camouflage, mimicry
Prey/Food - variants with adaptations allowing them to obtain food have more offspring
- e.g. Speed, senses for finding prey/food, weapons for killing prey or obtaining food, camouflage for stealth
Climate - those who can survive new climate best have more kids
- e.g. ice age, change in climate due to migration.
Mates - variants with adaptations allowing them to attract a mate to have offspring
- e.g. strong, attractive, good provider

17. Example #1: Escaping Predation Peppered Moth (see video clip)
Early trees had light-colored bark
Only the light-colored moths survived. Selection was for less melanin.
After industrialization, the tree bark was darker.
Only the darker colored moths now survived. Selection was for more melanin.
New info on the Pepper Moth experiment

19. Example #2: Obtaining Food
The neck of the Giraffe
Co-evolution with Acacia Trees
Selection pressure is source of food
The Red Queen Hypothesis...

20. Example #3 The leaf bug The selection pressure is predators
It’s strategy is to mimic a leaf
Pray Mantis Camouflage

21. Natural Selection
Or, how did we get here….

22. Natural Selection
The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous)
Charles Darwin ( ) saw three problems in need of a solution.
Darwin was not the only one to see these problems BTW
Other ‘Naturalists’ were struggling with the same issues

23. Problem the First
There is change over time in the flora and fauna of the Earth
What we would commonly call ‘evolution’ today
The fossil record showed this to be pretty clear, even to people in the mid 1800s
This was not controversial in Darwin’s time, and is not now.

24. The Second Problem
There is a taxonomic relationship among living things
People were big into classifying stuff
It was pretty obvious that there was a relationship between different species
Different birds, different grasses, different cats etc

25. The Third Problem Adaptation
Different kinds of teeth for different animals, say carnivore ripping teeth and herbivore grinding teeth
Different tissues within species
Heart vs. eye etc.

26. The Solution!
Natural Selection provides a mechanistic account of how these things occurred and shows how they are intimately related.
It is one of those ‘oh man is that ever easy, why didn’t I think of that?’ type things.

27. How’s it work? There is competition among living things
More are born or hatched or whatever, than survive and reproduce
Reproduction occurs with variation
This variation is heritable
Remember, there was NO genetics back then, Chuck knew, he just knew….
Realized that is wasn’t ‘blending’

28. How’s it Work?
Selection Determines which individuals enter the adult breeding population
This selection is done by the environment
Those which are best suited reproduce
They pass these well suited characteristics on to their young

29. How’s it Work?
REPRODUCTION is the key, not merely survival

30. This lecture keeps evolving…..
Survival of the Fittest (which Chucky D NEVER said) means those who have the most offspring that reproduce
So, the answer to the trilogy of problems is:
‘Descent with modification from a common ancestor, NOT random modification, but, modification shaped by natural selection’

31. Other Evolutionary Theories
Lamarckism
Inheritance of acquired characteristics
E.g., giraffes really wanted leaves, so they stretched their necks and…..
Sounds crazy, but a lot of people think this way
‘We will all have giant heads and tiny bodies someday’
‘Cave swelling fish don’t use their eyes so they disappear’
‘We don’t use our appendix so it is disappearing’

32. Silly incorrect evolutionary theories and ideas
Orthogenesis
There is some plan to evolution.
NO WRONG INCORRECT, THANKS FOR PLAYING
The idea of an ‘evolutionary ladder’ fits in here
It is wrong too……

34. Problem 3
If you observe a population and find that 16% show the recessive trait, you know the frequency of the aa genotype. This means you know q2. What is q for this population?

35. Evolution of populations
Evolution = change in allele frequencies in a population
hypothetical: what conditions would cause allele frequencies to not change?
non-evolving population
REMOVE all agents of evolutionary change
very large population size (no genetic drift)
no migration (no gene flow in or out)
no mutation (no genetic change)
random mating (no sexual selection)
no natural selection (everyone is equally fit)

36. 5 Agents of evolutionary change
Gene Flow
Non-random mating
Genetic Drift
Selection
Mutation 36

37. Application of H-W principle
Sickle cell anemia
inherit a mutation in gene coding for hemoglobin
oxygen-carrying blood protein
recessive allele = HsHs
normal allele = Hb
low oxygen levels causes RBC to sickle
breakdown of RBC
clogging small blood vessels
damage to organs
often lethal

38. Sickle cell frequency High frequency of heterozygotes
1 in 5 in Central Africans = HbHs
unusual for allele with severe detrimental effects in homozygotes
1 in 100 = HsHs
usually die before reproductive age
Sickle Cell:
In tropical Africa, where malaria is common, the sickle-cell allele is both an advantage & disadvantage. Reduces infection by malaria parasite.
Cystic fibrosis:
Cystic fibrosis carriers are thought to be more resistant to cholera:
1:25, or 4% of Caucasians are carriers Cc
Why is the Hs allele maintained at such high levels in African populations?
Suggests some selective advantage of being heterozygous…

39. Malaria
Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells 1 2 3

40. Heterozygote Advantage
In tropical Africa, where malaria is common:
homozygous dominant (normal)
die or reduced reproduction from malaria: HbHb
homozygous recessive
die or reduced reproduction from sickle cell anemia: HsHs
heterozygote carriers are relatively free of both: HbHs
survive & reproduce more, more common in population
Hypothesis:
In malaria-infected cells, the O2 level is lowered enough to cause sickling which kills the cell & destroys the parasite.
Frequency of sickle cell allele & distribution of malaria

41. Hardy-Weinberg lab pod cast

42. Lab—Part A Non-Tasters=Homo recessive (aa)
PTC
Control
Non-Tasters=Homo recessive (aa)
Tasters=Homo Dominant (AA) or Heter (Aa)
Figure out the p2 and 2pq for our class

43. Results and Discussion
5 Hardy Weinberg calculations
Show work—organzied part A-E
Discussion: In part A evolution did/did not happen because…. In part B…. In part C
Explain WHY, use terms

44. Part B—Testing an ideal Population
Initial Class Frequencies GG____ Gg____ gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
GG____ Gg____ gg ___

45. Part C—Selection (homo recessive selected against)
Initial Class Frequencies GG____ Gg____ gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
GG____ Gg____ gg___

46. Part D—Heterozygous Advantage (Homo dom—may die of maleria (flip coin; homo recessive—die of sickle cell)
Initial Class Frequencies GG____ Gg 24/48 gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
GG 16/48 Gg 32/48 gg 0/48

47. Part E—Genetic Drift (break into 3 smaller populations—make hypothesis)
Initial Class Frequencies GG____ Gg____ gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
Frequencies GG____ Gg____ gg___