Darwin’s Dangerous IdeasDarwin’s Dangerous Ideas

Unit 6: Evolution & Natural Selection

Basic DefinitionsBasic Definitions

• Evolution: Evolution: the process of change over timethe process of change over time• evolution is a change in the genetic makeup of a evolution is a change in the genetic makeup of a

population of interbreeding individuals within a population of interbreeding individuals within a species.species.

• Natural Selection: Natural Selection: survival of the fittestsurvival of the fittest• the process whereby some organisms in a the process whereby some organisms in a

species have certain inherited variations that species have certain inherited variations that give them an advantage over others.give them an advantage over others.

• Species have changed through time Species have changed through time and are related by descent from a and are related by descent from a common ancestorcommon ancestor

• The primary mechanism of The primary mechanism of Evolutionary Change is Natural Evolutionary Change is Natural SelectionSelection

Darwin’s Theory of Evolution Darwin’s Theory of Evolution by Natural Selectionby Natural Selection

1.1. Individuals within Individuals within a population or a population or species show species show variation in some variation in some featuresfeatures

2. There is hereditary 2. There is hereditary similarity between similarity between parents and their parents and their offspringoffspring

Darwin provided a mechanism for Darwin provided a mechanism for evolutionary change evolutionary change Natural Selection Natural Selection

3. In every generation, 3. In every generation, more offspring will more offspring will be produced than be produced than can survivecan survive

4. Each variant has a 4. Each variant has a characteristic characteristic survival and/or survival and/or reproductive reproductive successsuccess

An individual’s ability to survive and reproduce is called “fitness”

1 starfish --> 1079 offspring in 16 years

Darwin provided a mechanism for Darwin provided a mechanism for evolutionary change --> Natural Selectionevolutionary change --> Natural Selection

If the above things are met and the If the above things are met and the environment remains constant, the environment remains constant, the composition of the species will tend composition of the species will tend

towards an increase of the variant with towards an increase of the variant with the highest reproductive success.the highest reproductive success.

Can selection produce Can selection produce evolutionary change?evolutionary change?

• Hypothesis: Natural selection is the primary mechanism through which organisms have evolved over long periods of time

• Prediction: selection can lead to small evolutionary changes in short periods of time

-example - artificial selection-direct observations: Darwin’s finches, Biston moths, antibiotic resistance in bacteria, herbicide resistance in weeds

Artificial SelectionArtificial Selection

Biston Biston Moths: a Classic exampleMoths: a Classic exampleSelection in peppered moths in England by H.B.D. Kettlewell

2 genetically determined phenotypes: black, mottled white

Prior to 1600 (industrial revolution)black form approximately 1%white form approximately 99%

After 1600 (widespread pollution, smoke and soot)black form approximately 90%white form approximately 10%

Now (local pollution from smokestacks)Near Pollution Away

black form 50% 10%white form 50% 90%

An example of Natural Selection in Action: An example of Natural Selection in Action: Galápagos FinchesGalápagos Finches

Implications of Natural SelectionImplications of Natural Selection• Natural selection acts on individuals, but its Natural selection acts on individuals, but its

consequences occur in populationsconsequences occur in populations

• Natural Selection Acts on Phenotypes, but Natural Selection Acts on Phenotypes, but Evolution consists of changes in gene Evolution consists of changes in gene frequenciesfrequencies

• Natural Selection is backward-looking, Natural Selection is backward-looking, not forward lookingnot forward looking

Implications of Natural SelectionImplications of Natural Selection

• Natural Selection acts on existing traits Natural Selection acts on existing traits

• Natural Selection does not have a goal Natural Selection does not have a goal nor is it "progressive” nor is it "progressive”

• Natural Selection acts on individuals, Natural Selection acts on individuals, not groupsnot groups

Apple Maggot Flies: The Apple Maggot Flies: The evolution of a new speciesevolution of a new species

Rhagoletis pomonella

Recently, the species R. pomonella shifted from its native host to introduced, domestic apples (Malus pumila)

Rhagoletis lays its eggs in fruit to develop -->Original host = hawthorn trees

Now: two genetically distinct groups that do not interbreed

The idea of evolution was developed from many observations of life. It has been tested and challenged many times and in many ways, and has survived in great shape.

There are also many independent lines of evidence which are consistent with evolution as a real process.

There is NO observed evidence against evolution.

Evolution therefore holds the high status of near certainty.

Conclusion: Evolution is as Conclusion: Evolution is as good as great science gets!good as great science gets!

OK, Any Questions So Far?OK, Any Questions So Far?

Maybe now would be a good time Maybe now would be a good time for a break…for a break…

Discussion Question:Discussion Question:Are humans still evolving?Are humans still evolving?

Common Common Misperception:Misperception:

“And now there go the Wilsons!... SeemsLike everyone’s evolving except us!”

Individualsevolve

Acquired characteristics Acquired characteristics are not inherited!are not inherited!

Common Misperception:Common Misperception:

Timmy & GobblesTimmy & Gobbles

Classroom Assignment:Classroom Assignment:Building the Perfect BeastBuilding the Perfect Beast- I want you to think about how life forms - I want you to think about how life forms

have evolved over time, and how they have evolved over time, and how they might have evolved better.might have evolved better.

- Today you are in charge of the world, - Today you are in charge of the world, and you have to think about ways to and you have to think about ways to make species better adapted to the make species better adapted to the environment.environment.

Building the Perfect BeastBuilding the Perfect Beast

• Pick Six Characteristics of Humans that Pick Six Characteristics of Humans that you think should be improved (you think should be improved (height, height,

speed, vision, etc.speed, vision, etc.))

• Design a new human, describing your Design a new human, describing your six improvements in detail, writing a six improvements in detail, writing a short paragraph for each improvementshort paragraph for each improvement