Arguments & evidence
How incredibly stupid not to have thought of that
Thomas Huxley
Arguments
Blending inheritance
Variability
Isolation
Age of the earth
Arguments
Blending inheritance
-new adaptations diluted with each generation
Darwin’s reply:
Favorable traits maintained if popln isolated
Some traits ‘preponent’
Adaptive traits arise often
Enhanced reproduction of favorable traits
Arguments
Variability
-Darwin confined natural selection to small,
continuous variation
How could new spp arise from small variations?
-successive change through time
How could small variations confer an advantage?
-Darwin could not answer, later demonstrated
How could selection act on a nonexistent trait?
-preadaptation - new organ modified from another
1% per generation change in anatomy
<500000 yrs
Arguments
Isolation
-how could a new spp evolve in close
proximity to its parents
Darwin did not emphasize isolation as a
primary cause for evolution
Arguments
Age of the earth
-earth was not old enough to allow time
for evolution
Biblical
5,000
Newton
50,000
Buffon
75,000
Kelvin
100,000,000
present
4,500,000,000
Arguments
Blending inheritance
Variability
Isolation
Age of the earth
Evidence
Systematics
Geographic distribution
Comparative anatomy
Embryology
Fossils
Artificial selection
Direct observation
Evidence
Systematics
-gradation of species easily understood by
evolutionary relationships
Evidence
Geographic distribution
-evolutionarily related organisms geographically
connected
Evidence
Geographic distribution
-evolutionarily related organisms geographically
connected
marsupial radiation
Evidence
Comparative anatomy
homologous/analogous organs
Evidence
Comparative anatomy
homologous/analogous organs
Darwin’s interpretation of homology has become the
definition: similarity due to common ancestry
Evidence
Comparative anatomy
homologous/analogous organs
Organisms show curious similarities in structure and
development unrelated to function
Evidence
Comparative anatomy
convergent evolution
Evidence
Comparative anatomy
vestigial organs
Evidence
Comparative anatomy
vestigial organs
whale ancestor
modern whale
femur
Organisms have vestigial structural, developmental and
molecular traits
Vestigial structures are a manifestation of change
through time
Evidence
Embryology
-remarkable similarity among diverse vertebrates
Evidence
Fossils
-vast majority of fossil forms differ from extant spp
extinction
succession
transitional forms
environmental changes
Evidence
Fossils
-vast majority of fossil forms differ from extant spp
extinction
The fact that many species have gone extinct
suggests that Earth’s flora and fauna have
changed over time
Evidence
Fossils
-vast majority of fossil forms differ from extant spp
transitional forms
Evidence
Fossils
-vast majority of fossil forms differ from extant spp
“living fossils”
Evidence
Fossils
-vast majority of fossil forms differ from extant spp
extinction
succession
transitional forms
environmental changes
Evidence
Artificial selection
-accelerated evolution based on human-favored
traits
Evidence
Artificial selection
-accelerated evolution based on human-favored
traits
Evidence
Direct observation
-natural selection can be observed in real time
Observations on living organisms show that populations
and species change over time