1. The Theory of Evolution

2. 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
We are all in the same “tree of life”

4. The Definition of Evolution
Evolution is….
Descent with Modification
Small-scale evolution: Changes in gene frequency in a population from one generation to the next. (microevolution)
Large-scale evolution: The descent of different species from a common ancestor over many generations. (macroevolution)

5. Which of these represents descent with modification?
In this example, what exactly is being modified?
Phenotypic traits of a population are modified over time.
This is measurable as changes in
“allele frequencies”
Big Beetles go through a drought and have limited food
Next generation is physically smaller due to lack of food or
90% of the beetles have the gene for green color
30% of the beetles have the gene for green color

6. A change in allele frequencies in a population is evidence of microevolution
Let’s further study how allele frequencies can change in an activity called “Breeding Bunnies”

7. Basic requirements of Micro-evolution
There is variation in traits. (diversity)
There is differential reproduction.
Due to selective forces in the environment, 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.

8. How do populations introduce variation or diversity?
Mutation
A change in a DNA sequence
usually 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.

9. How do populations introduce variation or diversity?
Migration (Gene Flow)
Individuals from one group move into another group.
Brings in new genes or changes frequency of genes 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

10. How do populations introduce variation or diversity?
Let’s consider the following game of chance to find out
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.
But does genetic drift always increase diversity?
                                                                                     
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.

11. 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:
How does the diversity of the 4th generation compare to that of the starting population?
The variation has __________ in response to selective pressures
decreased

12. What effect does genetic drift have on smaller populations?
Genetic drift acts faster and has more drastic results in smaller populations. This effect is particularly important in rare and endangered species.
Population Bottle Neck

13. 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

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

15. Driftworm Activity
Turn your intNB to the driftworm activity, and get out:
Five colored pencils
Color in Generation 0 of your driftworms

16. Driftworm Activity Each of these worms reproduces asexually
The population size is constant
The generations do not overlap
These are haploid organisms

17. Driftworm Activity Roll the die.
This number represents which worm survives (by chance)and can be colored in for the next generation.
Do this four more times.

18. Driftworm Activity Repeat this in as many generations as possible
That is, until there is only one phenotype “fixed” in the population.

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

20. Genetic variation (diversity) is required for what micro-evolutionary process?

21. 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.

22. Natural Selection fittest
It is often called “survival of the _________.” “Fit” often refers to a phenotype’s success in reproducing. But… is this term accurate? Is it always the biggest, fastest, strongest? Let’s read a cartoon about natural selection to find out…

23. Types of Selection Artificial Selection:
People choose plants and animals with desirable traits to reproduce.
Nature does NOT select.

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

25. Types of Selection Stabilizing Selection:
Genetic Diversity decreases as a population stabilizes on a particular genetic trait.
Extreme traits are selected against.
The desert population of spiny cacti are under attack. Peccaries are eating those plants with low-spine-number causing their alleles to vanish from the gene pool and enriching the remaining gene pool in those alleles that create cacti with high-spine-numbers.Just as the community of cacti and peccaries are adjusting to one another, a second predator, a parasitic insect, arrives in the study area.
This insect lays its eggs at the base of the cacti's spines. When the grubs hatch, they bore into the cacti to eat the soft inner pulp, to grow, to pupate, and to emerge as new adults later in the year.
Preferring densely spined cacti, these egg-laying parasites more often destroy varieties of plants with larger numbers of spines. An infested cactus rarely survives.
In this new situation, with the cactus population under attack from a predator and a parasite, both extremes of spine value are being removed.
Peccaries are consuming the low-spine-number plants, and the insects are killing the high-spine-number plants. As these gene combinations are removed from the cactus gene pool, there is less and less variety possible in subsequent generations.
The distribution curve plotted year after year becomes sharper and narrower, "tightening up" around a limited spine number that just survives both types of killers.
This is called stabilizing selection even though diversity is decreased and such populations are actually very fragile. These plants can be easily eliminated, and sent into extinction, if the environment changes once more. Further evolution away from the most common variety is unlikely.

26. Types of Selection Disruptive Selection:
Selection that favors the extremes of the distribution
A population of spiny cacti is in genetic equilibrium, with no forces of selection acting on it, the distribution curve of number of cacti showing a particular number of spines is broad and symmetrical.A road is built quite close to the study site, which keeps away the peccaries and the parasitic insects, but with the road comes the tourists.
In many desert areas of the United States, passing cactus aficionados like to pick up a souvenir cactus to take home with them after a day-trip out into the desert. This is a serious problem in some areas because the tourists always take the better looking cacti, and these happen to be the ones with the middle-spine-numbers.
Years of collecting have left their toll on the roadside cacti. In this environment, it is maladaptive to be good looking and have a reasonable number of spines. Low-spine-number plants are not picked because they don't "look right", and high-spine-number varieties are left alone because they are too hard to pick.
Gradually, the gene pool changes in favor of the two extreme spine number types. Disruptive selection works against those phenotypes that fall into the midrange of values.

27. Overview of the types of selection

28. 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

29. 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

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

31. 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!

32. What about odd features that don’t seem to serve any selective function?
Vestigial Structures
An inherited feature that is now functionless and usually less elaborate than in the ancestor.
Formed when a species experiences a different set of selective pressures than its ancestors, and selection to maintain the elaboration and function of the feature ends.

33. 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
   
                              

35. Coevolution
A process in which two or more different species reciprocally effect each other’s evolution.
species A evolves, which causes species B to evolve, which causes species A to evolve, which causes species B to evolve, etc.
For ex. Co-Evolution of Computer – virus A B

36. Types of Coevolution Predator/prey and parasite/host
Competitive species
Mutualistic species
Like plants and pollinators

37. Macroevolution (Speciation)
Form of large-scale evolution
Descent of different species from a common ancestor
What evidence is there for macroevolution?

38. 1. Fossil Record

39. 2. Geographic Distribution of Living Species

40. 3. Homologous Body Structures

41. 4. Vestigial Organs

42. 5. Similarities in Early Development

43. Mechanism of Macroevolution
For macroevolution to occur, two populations must be reproductively isolated (or separated) from one another
Green blends in with grass
Brown blends in with tree trunks
The separated population experience different selective pressures
Over time, they evolve in separate directions, into different species that cannot interbreed

44. What is a species?
Two populations that can mate and produce fertile offspring.
Ex. donkeys and horses are considered different species because they produce mules, that are not fertile.
But… all breeds of dogs are the same species
“mutts” are still fertile

45. Does speciation occur gradually or suddenly?
Punctuated Equilibrium:
Species stay relatively unchanged over time
Speciation is driven by major events that drastically change the environment, forcing rapid evolution
Evolution occurs in rapid bursts, as supported by gaps in the fossil record.
Gradualism:
Phenotypic changes due to evolution accumulate slowly over time
Speciation occurs gradually

46. Does speciation occur gradually or suddenly?
Speciation occurs both gradually and punctually
There is evidence to support both ideologies