- Mockingbirds
Darwin began to think… could the variation WITHIN species eventually lead to variation BETWEEN species?
Could organisms in a species become so different that they become different species?

C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration from Americas

C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration
- But if ancestors migrated from Americas,

C. Observations
4. Biogeography – Island Faunas
- How did these animals get here?
Everything points to migration
- But if ancestors migrated from Americas, then the species must have changed over time into the species we observe there today….
Because they are not the same.

C. Observations
5. Argument:
P1: Species that are alive today are different from those that have lived previously. (Fossil Record)

C. Observations
5. Argument:
P1: Species that are alive today are different from those that have lived previously.
P2: Spontaneous Generation is refuted, so organisms only come from other organisms. (Experimentation)

C. Observations
5. Argument:
P1: Species that are alive today are different from those that have lived previously.
P2: Spontaneous Generation is refuted, so organisms only come from other organisms.
C1: Thus, the organisms alive today must have come from those pre-existing, yet different, species.

C. Observations
5. Argument:
P1: Species that are alive today are different from those that have lived previously.
P2: Spontaneous Generation is refuted, so organisms only come from other organisms.
C1: Thus, the organisms alive today must have come from those pre-existing, yet different, species.
C2: There must have been change through time (evolution).

C. Observations
5. Argument:
P1: Species that are alive today are different from those that have lived previously.
P2: Spontaneous Generation is refuted, so organisms only come from other organisms.
C1: Thus, the organisms alive today must have come from those pre-existing, yet different, species.
C2: There must have been change through time (evolution).
Corollary: The fossil record, vestigial organs, and homologies are all explicable and logical in this context, and inexplicable
(even heretical) in some theological contexts (imperfection).

I. Darwin’s Contributions
A. His Life
B. Origin of Species
C. Observations
D. Hypothesis – How Change Occurs

D. Hypothesis – How Change Occurs
1. Transitional Observations a. Domesticated Animals

D. Hypothesis – How Change Occurs
1. Transitional Observations a. Domesticated Animals

D. Hypothesis – How Change Occurs
1. Transitional Observations a. Domesticated Animals
Humans can change the characteristics of a species by
‘selecting’ for particular traits. This can lead to the expression of extreme variation, well beyond the original range of variation in the initial group.
Selection can create …. There are no wolves that are as small as Chihuahuas…

D. Hypothesis – How Change Occurs
1. Transitional Observations b. 1844: Darwin Reads Malthus Essay On the Principle of Population (1798)
Thomas Malthus (1766-1834)

D. Hypothesis – How Change Occurs
1. Transitional Observations b. 1844: Darwin Reads Malthus Essay On Population
P1: All populations have the capacity to ‘over-reproduce’

D. Hypothesis – How Change Occurs
1. Transitional Observations b. 1844: Darwin Reads Malthus Essay On Population
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite

D. Hypothesis – How Change Occurs
1. Transitional Observations b. 1844: Darwin Reads Malthus Essay On Population
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”… most offspring born will die before reaching reproductive age.

D. Hypothesis – How Change Occurs
2. Natural Selection
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”
P3: Organisms in a population vary, and some of this variation is heritable

D. Hypothesis – How Change Occurs
2. Natural Selection
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”
P3: Organisms in a population vary, and some of this variation is heritable
C2: Some organisms, as a consequence of their inherited traits, will be more likely to survive and reproduce than others.
There will be “differential reproductive success.”

D. Hypothesis – How Change Occurs
2. Natural Selection
C2: Some organisms, as a consequence of their inherited traits, will be more likely to survive and reproduce than others.
There will be “differential reproductive success.”
C3: So, adaptive traits will be passed on in a population at higher frequency than less adaptive traits. These adaptive traits will accumulate in a population. The population will change over time. LINEAGE EVOLUTION.

D. Hypothesis – How Change Occurs
2. Natural Selection
C2: Some organisms, as a consequence of their inherited traits, will be more likely to survive and reproduce than others.
There will be “differential reproductive success.”
C3: Over time, adaptive traits will be passed on in a population at higher frequency than less adaptive traits. These adaptive traits will accumulate in a population. The population will change over time. LINEAGE EVOLUTION.
Corollary: Two populations, adapting to different environments, will become different from one another; perhaps so different that they are unable to mate, and are different species
RADIATIONAL EVOLUTION.