The Evidence for Evolution
Consider a sample problem
Problem: How did the great diversity of life originate?
Alternative Solutions:
A. All living things were created at the same time in
their current form. Basis: traditional biblical interpretation
B. Different types of living things were created at different
times. Basis: modified biblical interpretation
C. Different types of living things evolved from earlier
types. Basis: Darwin inferred from difficulties in the classification
of living things: some organisms do not fit into discrete categories
Fair Test #1
A fair test:
does not have the same basis as any of the alternative solutions
could support any of the alternative solutions
The fossil record as a fair test:
1. If alternative A) is correct, we should see fossils of all
organisms mixed together at all levels (for all time), in particular sequence
2. If alternative B) is correct, we should see staggered appearance
of different types, with novel traits suddenly appearing, and showing
little or no change to the present
3. If alternative C) is correct, we should see staggered appearance
of different types, showing gradually accumulating modifications of traits
from earlier forms to the present
Results of Fair Test #1
Observations and dating of
fossils clearly and consistently
provide data consistent with
alternative (C) and not with
(A) or (B).
Other fair tests to consider:
1. Chromosome banding patterns, comparing living groups
2. Amino acid sequences in proteins, comparing living groups
3. Base pair sequences in DNA, comparing living groups
4. Comparative anatomy studies of different groups
5. Comparative studies of development of different groups
Most Scientific Theories have 2
components
• A statement that summarizes a series of
observations
• A process that produces the pattern or set of
observations
Darwin’s Theory of Evolution by
Natural Selection
• Species have changed through time and
are related by descent from a common
ancestor
• The primary mechanism of Evolutionary
Change is Natural Selection
Why do Scientists accept
evolution over other
alternatives for the
explanation of the diversity of
living organisms seen today?
Evidence that Species have
Changed Through Time?
• Hypothesis: Species have changed through
time
• Prediction: we should be able to find signs
of evolutionary history
- direct observation
- fossil record
- vestigial structures
Direct observation of Evolution
Fossil Record
The fossil record is the history of life recorded by remains from
the past. Most fossils are at least 10,000 years old.
1. Body Fossils
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
2. Trace Fossils
What is found?
- Fossils exist and fossil forms are unlike species living today
1. Fossil Sequence?
When fossils are arranged according to
their age, they show successive
evolutionary change
2. Fossil Intermediates?
Transitional fossils have been found between:
Amphibians & reptiles, reptiles & birds,
reptiles & mammals, apes and humans
The Evolution of Horses
A particularly well-documented case of evolution within a group
The fossil Record is Incomplete
At the time of Darwin, the fossil record was VERY scanty. A
great deal of progress has been made since, but it is far from
finished.
The fossil record is relatively incomplete for several reasons:
1. Soft tissues are rarely preserved
2. Movement of the earth's crust has obliterated and/or
covered many fossils
3. Fossilization takes place only in certain types of
habitats and favorable environments
4. Paleontologists have not dug up every place on earth
Even if there were no fossil
record, the evidence from living
organisms would be more than
sufficient to demonstrate the
historical reality of evolution
Vestigial Structures
• Features that have no apparent function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
• Typically have an important function in related spp.
Vestigial structures
Ex: Hindlimb
joints in whales
and snakes
Vestigial Structures in Humans
Tailbone
Wisdom Teeth
Appendix
Evidence for the Relatedness of
Life Forms?
• Hypothesis: all living organisms have
descended from a common ancestor
• Prediction: we should also be able to see
evidence of relatedness of species
-Homology
-Geographic distribution
Homology
• Homology: a similarity between species that
is the result from the inheritance of traits from a
common ancestor
•The features of every creature reflect history
as well as adaptation
• 3 types of homologies
- structural
- developmental
- genetic
Homology vs. Analogy
Natural selection appears to have favored similar adaptations
in unrelated organisms in similar environments-->
these structures are analogous
Whereas homologous structures
share structural similarity, but not
function, analogous structures
share function but not structural
similarity since they evolved
independently
Convergent Evolution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Homologous structures: bones of the forelimb
The underlying design of each structure is similar despite
their functional differences
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Embryos show evolutionary history
Homologous structures in adults develop from homologous groups
of cells in embryos --> they share developmental pathways
Genetic Homologies
All living organisms share the same
genetic code
Chromosome and gene similarities between
species match evolutionary similarities
This is true for both coding regions and
“junk DNA”
Molecules reflect evolutionary divergence
Geographic Distributions
Species that are extremely similar to one another tend to be
clustered geographically (Ex.: Darwin’s finches)
Living species are more similar to fossil species in the same area
than they are to living species in other areas
•The law of succession
–general correspondence between fossil and
living forms in same geographical area
Darwin used this observation to predict that fossils
of ancient humans should be found in Africa
That Evolution Has Occurred
Is A Fact