Transcript Darwin`s Dangerous Idea

Darwin’s Dangerous
Idea
Pre-Darwinian beliefs
1. Earth Is 10,000 Old (Ussher)
2. Species are fixed
Changing thought…
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?
The “Evolution” of Darwin’s Thinking
Before: Species Fixed and Unchanged
During: Questions the concept
After: Change as they adapt
Darwin’s Observations on the Beagle
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
Other Influences
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
Darwin’s Conclusions
1. Descent with modification
A. 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 Selection
A. 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 Selection
4 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
The Case of the Peppered Moth
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 (continued)
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.
Think about it!!
1. What do you think happened after tough
anti-pollution laws were passed and the
forests began to clear up (turn white
again)?