Darwin’s Dangerous Idea

1. Earth Is 10,000 Old (Ussher)

2. Species are fixed

Pre-Darwinian beliefs

1. Earth Is MUCH older (Buffon)

1. Sudden changes; catastrophism

2. Geologic Change; Earth Changes (Lyell)

2. Lamarckian Evolution

A. You don’t use it, you lose it!

*What are the problems with this theory?

Changing thought…

Before: Species Fixed and Unchanged

During: Questions the concept

After: Change as they adapt

The “Evolution” of Darwin’s Thinking

1. Fossils:

1. Old organisms no longer exist

2. Organisms descended from common ancestor

2. Evidence of earthquakes, mudslides

1. Land moving upward

2. Marine fossils on mountaintops

3. Distribution of Organisms- same habitat : different organisms

1. The Galopagos Finches

Darwin’s Observations on the Beagle

1. Thomas Malthus

A. Human populations grow faster than can be supported

B. Leads to a struggle for survival

C. Darwin transferred this idea to all populations

1) Population- group of same species that interact together

Other Influences

Darwin’s Conclusions

1. Descent with modificationA. Mutations may cause adaptations

1) Adaptations- an inherited trait that increases chance of survival.

2) Variation- differences in traits among members of same species

• Only very few mutations cause adaptations…

• most cause death or disease.

2. Natural SelectionA. Well adapted organisms have more

offspring than less adapted organisms.

B. Increases the frequency of the adaptation

1) Frequency- how often the adaptation appears

Natural Selection4 key components

• 1. Overproduction• 2. Variation• 3. Struggle for survival

– Selective pressures- the parts of the environment that make an organism better adapted

• 4. Differential reproduction

1. In the early 1800’s, 98% of peppered moths were white with dark spots.

A. This allowed them to blend in better on the light covered trees

B. This also allowed them to hide from their main predators, birds

The Case of the Peppered Moth

1. In the early 1800’s, about 2% of peppered moths were dark.

A. They stuck out…

B. And they were eaten more (hence only 2% !)

The Case of the Peppered Moth (continued)

1. In the Mid 1800’s the industrial revolution occurred in England.

2. The burning of coal created an abundance of black soot, which deposited on tree in the nearby forest.

3. Selective Pressure- factor that causes a particular trait to allow an organism to survive better

The Case of the Peppered Moth (continued)

1. Now the trees were darker, and the moths looked like this:

A. Which moths would be more likely to be eaten now?

The Case of the Peppered Moth (continued)

1. The dark moths survived better

They blended in…

A. And they were eaten less, therefore reproducing more

The Case of the Peppered Moth (continued)

1. The white moths stuck out more

They where eaten more frequently..

A. And therefore they reproduced less, causing them to decrease in number.

The Case of the Peppered Moth (continued)

1. What do you think happened after tough anti-pollution laws were passed and the forests began to clear up (turn white again)?

Think about it!!