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

5,000

50,000

75,000

100,000,000

Biblical

Newton

Buffon

Kelvin

4,500,000,000present

Arguments

Blending inheritance

Variability

Isolation

Age of the earth

Evidence

Systematics

Geographic distribution

Comparative anatomy

Embryology

Fossils

Artificial selection

Direct observation

EvidenceSystematics

-gradation of species easily understood by evolutionary relationships

EvidenceGeographic distribution

-evolutionarily related organisms geographically connected

EvidenceGeographic distribution

-evolutionarily related organisms geographically connected

marsupial radiation

EvidenceComparative anatomy

homologous/analogous organs

EvidenceComparative anatomy

homologous/analogous organs

Darwin’s interpretation of homology has become the definition: similarity due to common ancestry

EvidenceComparative anatomy

homologous/analogous organs

Organisms show curious similarities in structure and development unrelated to function

EvidenceComparative anatomy

convergent evolution

EvidenceComparative anatomy

vestigial organs

EvidenceComparative anatomy

vestigial organs

femur

whale ancestor

modern whale

Organisms have vestigial structural, developmental and molecular traits

Vestigial structures are a manifestation of change through time

EvidenceEmbryology

-remarkable similarity among diverse vertebrates

EvidenceFossils

-vast majority of fossil forms differ from extant spp

extinction

succession

transitional forms

environmental changes

EvidenceFossils

-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

EvidenceFossils

-vast majority of fossil forms differ from extant spp

transitional forms

EvidenceFossils

-vast majority of fossil forms differ from extant spp

“living fossils”

EvidenceFossils

-vast majority of fossil forms differ from extant spp

extinction

succession

transitional forms

environmental changes

EvidenceArtificial selection

-accelerated evolution based on human-favored traits

EvidenceArtificial selection

-accelerated evolution based on human-favored traits

EvidenceDirect observation

-natural selection can be observed in real time

Observations on living organisms show that populations and species change over time