1. The Theory of Evolution

2. Darwin’s Ideas Natural Selection
Background: Darwin
Darwin’s Ideas
Natural Selection
A process in which some individuals have genetically-based traits that improve survival or reproduction
Thus, they have more offspring surviving to reproductive age than other individuals.

3. Darwin’s Ideas Common Ancestry All life forms share a common ancestor
Background: Darwin
Darwin’s Ideas
Common Ancestry
All life forms share a common ancestor
We are all in the same “tree of life”

4. The Definition of Evolution
Background: Definition
The Definition of Evolution
Descent with Modification
Small-scale evolution: Changes in gene frequency in a population from one generation to the next
Large-scale evolution: The descent of different species from a common ancestor over many generations.
What exactly is being modified?

5. Which of these represents descent with modification?
Background: Definition
Which of these represents descent with modification?
Big Beetles go through a drought and have limited food
Next generation is physically smaller due to lack of food
90% of the beetles have the gene for green color
30% of the beetles have the gene for green color

6. How does this “descent with modification” happen?
Mechanism: 1. Mutation
How does this “descent with modification” happen?
Mutation
A change in a DNA sequence
usually occurring because of errors in replication or repair.
Mutation is the ultimate source of genetic variation.
A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.

7. How does this “descent with modification” happen?
Mechanism: 2. Migration
How does this “descent with modification” happen?
Migration
Individuals from one group move into another group.
Making the gene more frequent in the population.
Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.
gene flow

8. How does this “descent with modification” happen?
Mechanism: 3. Genetic Drift
How does this “descent with modification” happen?
3. Genetic Drift
In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals.
                                                                                     
Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.

9. Genetic Drift: A game of chance
Mechanism: 3. Genetic Drift
Genetic Drift: A game of chance
Imagine a game in which you have a bag holding 100 marbles
50 of which are brown and 50 green.
You are allowed to draw 10 marbles out of the bag.
Now imagine that the bag is restocked with 100 marbles
with the same proportion of brown and green marbles as you have just drawn out.
The game might play out like this:

10. What effect does Genetic Drift have on Evolution?
Mechanism: 3. Genetic Drift
What effect does Genetic Drift have on Evolution?
Drift reduces genetic variation in populations, potentially reducing a population’s ability to evolve in response to new selective pressures.
Genetic drift acts faster and has more drastic results in smaller populations. This effect is particularly important in rare and endangered species.
Genetic drift can contribute to speciation. For example, a small isolated population may diverge from the larger population through genetic drift.
                                                                                              
Population Bottle Neck

11. Examples of Genetic Drift
Mechanism: 3. Genetic Drift
Examples of Genetic Drift
Population Bottleneck
An event in which a population’s size is greatly reduced
Northern Elephant Seal
Event that causes the population to be reduced in size
Initial Diverse Population
Final population
Cheetah

12. Examples of Genetic Drift
Mechanism: 3. Genetic Drift
Examples of Genetic Drift
Founder Effect
Changes in gene frequencies that usually accompany starting a new population from a small number of individuals.

13. Driftworm Activity Put your IntNB to the side, and get out:
Mechanism: 3. Genetic Drift
Driftworm Activity
Put your IntNB to the side, and get out:
Your colored pencils and
The worksheet you picked up when you came in
Color in Generation 0 of your driftworms

14. Driftworm Activity Each of these worms reproduces asexually
Mechanism: 3. Genetic Drift
Driftworm Activity
Each of these worms reproduces asexually
The population size is constant
The generations do not overlap
These are haploid organisms

15. Mechanism: 3. Genetic Drift
Driftworm Activity
Roll the die and put a dot next to the corresponding worm.
Put a dot next to the corresponding number (the one you land on)
Do this five times (for each individual in the population)

16. Mechanism: 3. Genetic Drift
Driftworm Activity
Repeat this until one allele is “fixed” in the population.
That is, until there is only one phenotype in the population.

17. What factors prevent an allele from becoming “fixed” in a population?
Mechanism: 3. Genetic Drift
What factors prevent an allele from becoming “fixed” in a population?
Mutation
Migration (Immigration and Emigration)  this is sometimes called “gene flow”
Mating (Sexual Reproduction)
A large population (to avoid the effects of genetic drift)
and…
Use Bean example

18. How does this “descent with modification” happen?
Mechanism: 4. Natural Selection
How does this “descent with modification” happen?
Natural Selection
A process in which some individuals have genetically-based traits that improve survival or reproduction
They have more offspring surviving to reproductive age than other individuals.
                            
Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

19. Basic requirements of Natural Selection
Mechanism: 4. Natural Selection
Basic requirements of Natural Selection
There is variation in traits.
There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential.
There is heredity.
                            
There is variation in traits. For example, some beetles are green and some are brown.
There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.
There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

20. Types of Selection Selection
Mechanism: 4. Natural Selection
Types of Selection
On the left side of your IntNB, start a flow chart for selection:
As you record the examples of these types of selection in your notes, note the examples on your flowchart.
Selection
Natural
Selection
Artificial
Selection
Draw the bell curve below each term if there is one in the presentation.
Directional
Selection
Stabilizing
Selection
Disruptive
Selection

21. Types of Selection Artificial Selection:
Mechanism: 4. Natural Selection
Types of Selection
Artificial Selection:
Farmers and breeders have been only allowing plants and animals with desirable traits to reproduce.

22. Types of Selection Stabilizing Selection:
Mechanism: 4. Natural Selection
Types of Selection
Stabilizing Selection:
Genetic Diversity decreases as a population stabilizes on a particular genetic trait.
Extreme traits are selected against.

23. Types of Selection Disruptive Selection:
Mechanism: 4. Natural Selection
Types of Selection
Disruptive Selection:
Selection that favors the extremes of the distribution

24. Types of Selection Directional Selection:
Mechanism: 4. Natural Selection
Types of Selection
Directional Selection:
One allele is favored over another, and the population shifts in one direction

25. Which of type of selection is/can be caused by the following…
Mechanism: 4. Natural Selection
Which of type of selection is/can be caused by the following…
Human birth weight
Answer: Stabilizing Selection
The finches Darwin observed on the Galapagos Islands
Answer: Disruptive Selection
Lighter moths being selected by predators after the trees became covered with soot (post Industrial Revolution)
Answer: Directional Selection

26. Directional Selection
Mechanism: 4. Natural Selection
Directional Selection
Industrial Melanism Activity:

27. Directional Selection
Mechanism: 4. Natural Selection
Directional Selection
We will collect individual and class data and see if selection took place.
Draw the following data table in your IntNB.
When on White Paper
When on Newspaper
Number of White Moths Remaining
Number of Newspaper Moths Remaining

28. Natural Selection: A Case Study
Mechanism: 4. Natural Selection
Natural Selection: A Case Study
Could Natural Selection explain this?
On rocky shores, animals have ranges that form clear spatial patterns.
Tegula funebralis, a snail common on California shores
It is found in the Pacific in both Northern and Southern California
Some species live only in deep water, while some live much higher up the shore.
In Southern California, Tegula live high up on the shore
In Northern California, they live in deeper water.

29. Natural Selection: A Case Study
Mechanism: 4. Natural Selection
Natural Selection: A Case Study
Michael Fawcett thought so and formulated a hypothesis to test.
He found that predators, such as octopi, starfish, and crabs, were more abundant in southern California than in northern California.
How would you design an experiment to test Natural Selection at work?
Fawcett tested this hypothesis by transplanting snails.
He took northern and southern snails, released them in deep water and watched what happened.

30. Natural Selection: A Case Study
Mechanism: 4. Natural Selection
Natural Selection: A Case Study
If predators were around, all the snails high-tailed it towards higher ground (snails can probably sense the chemicals exuded by predators).
But southern snails moved further up the shore faster than northern snails.
Because the northern snails were slower and didn't move high enough, they were more likely to be eaten by predators.
What did this experiment show?

31. Natural Selection: A Case Study
Mechanism: 4. Natural Selection
Natural Selection: A Case Study
There is an innate difference between southern and northern snails. This difference is probably genetic.
This difference can lead to differential survival. If predation is intense, snails that move higher faster are more likely to survive.

32. What is the general way we refer to those who survive?
Mechanism: 4. Natural Selection
What is the general way we refer to those who survive?
Fitness:
a genotype’s success at reproducing
(the more offspring the genotype leaves, the higher its fitness).
Fitness describes how good a particular genotype is at leaving offspring in the next generation relative to other genotypes.
Is this always the biggest, fastest and strongest?

33. Let’s explore this Cartoon to find out…
Mechanism: 4. Natural Selection
Let’s explore this Cartoon to find out…
Take a minute to read the cartoon that was just handed out.
When you are through reading the cartoon, turn it over to indicate that you have read it.
Based upon your reading, does fitness always mean “the biggest, fastest and strongest”?
No. The “fit” cricket has adapted a strategy for reproducing without the “cost.”

34. Natural Selection: Adaptations
Mechanism: 4. Natural Selection
Natural Selection: Adaptations
Adaptations: Come in many forms and help the organism survive. It could be:
Behavioral: Behaviors that an organism does to survive
Functional: An adaptation in which one aspect of the organism has increased function in an environment
Structural: Physical features on an organism that enable it to survive.
Private Life of Plants video clip

35. Q: The following are examples of what type of adaptation?
Mechanism: 4. Natural Selection
Q: The following are examples of what type of adaptation?
Katydids blending in with their substrate.
Structural
A bird’s mating call
Behavioral
A protein working at human body temperature and denaturing at higher temperatures.
Functional

36. Q: The following are examples of what type of adaptation?
Mechanism: 4. Natural Selection
Q: The following are examples of what type of adaptation?
Echolocation in bats searching for food
Behavioral
A bird’s beak
Structural
The non-poisonous milk snake has a banding pattern similar, but not the same as a poisonous coral snake.
Structural: This is mimicry!

37. Mechanism: 4. Natural Selection
What about odd features that don’t seem to serve any selective function?
Vestigial Structures
A feature that an organism inherited from its ancestor but that is now functionless and usually less elaborate than in the ancestor.
Formed when a lineage experiences a different set of selective pressures than its ancestors, and selection to maintain the elaboration and function of the feature ends.

38. Misconceptions about Natural Selection
Mechanism: 4. Natural Selection
Misconceptions about Natural Selection
It is not “Survival of the Fittest;” really it is “Survival of the ‘fit enough’”
Recessive alleles for disease can stay unnoticed in a population
Organism does not choose
Perfection is not obtained
Deleterious Genes:
Sickle Cell Trait
   
                              

39. Coevolution is the evolutionary “arms race”
Evolution in Action: Coevolution
Coevolution
A process in which two or more different species reciprocally effect each other’s evolution.
For example, species A evolves, which causes species B to evolve, which causes species A to evolve, which causes species B to evolve, etc A B
Coevolution is the evolutionary “arms race”

40. Types of Coevolution Predator/prey and parasite/host
Evolution in Action: Coevolution
Types of Coevolution
Predator/prey and parasite/host
Competitive species
Mutualistic species
Like plants and pollinators