Darwin’s Dangerous IdeasAnother Review…

Evolution & Natural Selection

Basic 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 Species have changed through time and are related by time and are related by descent from a common descent from a common ancestorancestor

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

Darwin’s Theory of Evolution by Natural Selection

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

2. There is 2. There is hereditary hereditary similarity similarity between between parents and parents and their offspringtheir offspring

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

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

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

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

1 starfish has 1079 offspring in 16 years

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

If the above four things are met, and If the above four things are met, and the environment remains constant, the 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 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: Biston moths,

antibiotic resistance in bacteria, herbicide resistance in weeds

Artificial Selection – an example

Biston Moths: a Classic ExampleSelection in peppered moths in England by Kettlewell

2 genetically determined types: black & mottled white

Prior to 1700 (industrial revolution)black form approximately 1%white form approximately 99%

After 1700 (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%

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 Individuals, but Natural Selection Acts on Individuals, 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

The idea of evolution was developed from many observations of life over the centuries.

It has been tested and challenged many times and in many ways, and has survived in great shape.

There is NO observed evidence against evolution.

Evolution therefore holds the high status of near certainty.

Discussion Question:Are humans still evolving?

Common Misperception:

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

Individualsevolve

Acquired characteristics are not inherited!

Common Misperception:

Timmy & GobblesTimmy & Gobbles

Classroom Assignment:Building a More Perfect Human

I want you to think about how the human I want you to think about how the human body has evolved over time, and how it body has evolved over time, and how it 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 the human species better.make the human species better.

Building a More Perfect Human• Address Six Characteristics of Humans Address Six Characteristics of Humans

that you think should be improvedthat you think should be improved

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

• Draw me a picture of your perfect beastDraw me a picture of your perfect beast

OK, Any Questions So Far?

If not, get to work on your perfect human…If not, get to work on your perfect human…