Darwin's Theory

2. What is a Theory?
• Everyday Language
– Hunch; Guess
• Scientific Language
– Created after years
of experiments and
observation
– Based on testable
evidence
– Stood the test of
time Based on gravitational theory, what
do you think would happen if I
dropped a pen?

3. Evolution Video Part I:
Just a Theory

4. • Acquired Inheritance: Early
theory where changes
acquired over a lifetime
could be passed to
offspring
• Ex: Evolution of the giraffe
neck
– Short neck ancestors
stretched their necks to
reach leaves
– Stretched neck was passed to
offspring
• Problem: Only traits linked
to DNA can be passed to
offspring

5. Silly Example of Acquired Inheritance
Meet
Jacob
Jacob is
in a car
crash
Jacob lost
his left
arm
If Jacob
has
children
in the
future,
how
many
arms will
they
have?

6. Debate Over Geologic Change
• Early belief:
– Earth ~6,000 years old
– Life remained unchanged
• “New” Observations
– Rock layers (strata) contained
differing fossils
– Deeper fossils (older) less
complex
– Environmental changes
thought to affect life
characteristics

7. Charles Darwin
• Observations:
– Organisms have variations
based on their
environment
– Variations provide
advantages
– Similarities between extinct
fossils & modern life
– Marine fossils atop
mountains
• Natural Selection: Process
where organisms with
favorable traits survive and
reproduce
• 1859: Published The Origin of
Species
Notch in shell
Survive in areas with higher vegetation
No notch in shell
Survive in areas with ground vegetation
So how did giraffes get a long neck?
Those with short necks died. Those with longer
necks survived and reproduced

8. Evolution Video Part II:
Who was Charles Darwin

9. Adaptation vs. Variation
• Variation: Inherited traits that make an individual different
from others
– Ex: Galapagos finches vary in their beaks
• Adaptation: Variation that increases the chance of survival
– Ex: Which finch would be better adapted to an island with large seeds for food?
Variation
1
Variation
2

13. Natural Selection in Action:
The Peppered Moth Analysis
Before the industrial revolution, the trees in the forest around Manchester,
England were a light grey/green due to the color of lichens (fungus) on their
trunks.

14. Natural Selection in Action:
The Peppered Moth Analysis
Peppered moths, or Biston betularia, which lived in the area were found in two
varieties: 1) Light with dark spots (most common) and 2) Dark with light spots
(less common).

15. Natural Selection in Action:
The Peppered Moth Analysis
Because there were not enough resources to support the entire population, the two varieties of
this species had to compete for survival. Their coloring, when against a similar background,
served as camouflage against predators such as birds and lizards, thus increasing chances of
survival.

16. Natural Selection in Action:
The Peppered Moth Analysis
As the Industrial Revolution progressed, the trees became covered with sulfur
dioxide, which killed the light colored lichen and thus turning the tree trunks
dark.

17. Year 1 Background Year 10 Background
Light peppered moth
Dark peppered moth

18. Year 1: Peppered Moths
Light
556
Dark
64

19. Year 10: Peppered Moths
Light
56
Dark
638

20. 1) What is a theory?
2) What did acquired inheritance state and how was it thought to
work?
3) What does natural selection state and how is it thought to work?
4) How can the general age of rocks (and fossils) be determined?
5) How does a variation and adaptation differ?
Review