Chapter 22
Descent with
Modification:
A Darwinian View of Life
Question?
How
did the diversity of life
originate?
Through the process of
Evolution.
Evolution
The
processes that have
transformed life on earth
from its beginnings to today's
diversity.
Evolution is the most
pervasive principle in
biology.
Teaching
Philosophy on
Evolution
Evolution
Has
itself "evolved" or
changed over time.
Illustrates “Science as a
Process”.
Pre-Darwinian Views
1. Greeks
2. Fixed Species
3. Catastophism
4. Hutton and Lyell
5. Lamarck
Greek Philosophers
1. Plato - Organisms are
already perfectly adapted to
their environments.
2. Aristotle - Organisms
arranged on a “scale of life”
from simple to complex.
Result
No
evolution.
Life is already perfect and
doesn’t need to change.
All the rungs on life's "ladder"
are already occupied.
Fixed Species Concept
The
creator had designed
each and every species for a
particular purpose.
Result
No
evolution.
Created the viewpoint that all
species could be identified
and named (Taxonomy).
A major factor in the
Linnaeus classification
system.
Catastrophism
Georges
Cuvier
(1769-1832).
Attempted to
relate fossils to
current life.
Theory
Fossils
were the remains of
species lost due to
catastrophe.
No new species originated;
species could only be lost
over time.
Result - No evolution.
James Hutton
1795
- Gradualism
Profound change is the
cumulative product of slow,
but continuous processes.
Result
Changes
on the earth were
gradual, not catastrophic.
Charles Lyell
1797
- 1875.
Incorporated
Hutton’s
gradualism into a
theory called
Uniformitarianism.
Uniformitarianism
Geological
processes have
operated at the same rate
over the Earth’s history.
Result
The
Earth must be VERY old.
(much older than 6000 years
of the fixed species concept).
Idea that slow and subtle
processes can cause
substantial change.
Jean Baptiste Lamarck
Published
theory in 1809.
Theory - Life
changed from
simple to
complex over
time.
Lamark
Fossils
were the remains of
past life forms.
Evolution did occur.
Mechanisms
1. Use and Disuse Body
parts used to survive
become larger and stronger.
Body parts not used to survive
deteriorate.
Mechanisms
2. Acquired Characteristics
Modifications
acquired by
use/disuse were passed on to
offspring.
Problem
No
knowledge of genetics.
Acquired traits are not
transmitted offspring.
Lamarck’s Credits
Did
suggest correctly the role
of fossils in evolution.
Did suggest that adaptation
to the environment is a
primary product of evolution.
Charles Darwin
Father
of the
modern theory
of evolution.
Theory Descent with
Modification.
Darwin's Background
Trained
as a Naturalist (after
trying religion and medicine).
Voyage of the Beagle
Result
Darwin's
training and travel
opportunities allowed him to
formulate and support his
ideas on Natural Selection.
Galapagos Finches
Alfred Wallace - 1858
Paper
on Natural
Selection
identical to
Darwin's ideas.
Result - July 1, 1858
Dual
presentation of the
Wallace-Darwin ideas to the
Linnaean Society of London.
Darwin - 1859
Publication
of
"The Origin of
Species”
Comment
Darwin
best remembered for
the theory because of his
overwhelming evidence and
because he published.
Darwinian View
History
of life is like a tree
with branches over time from
a common source.
Current diversity of life is
caused by the forks from
common ancestors.
Example
“The Origin of Species”
Documented
the occurrence
of evolution.
Suggested that the
mechanism for evolution was
Natural Selection.
The Facts:
Fact 1 All species
reproduce
themselves
exponentially.
Fact 2 - Most populations are
normally stable in size.
Fact 3 - Natural Resources are
limited (finite).
Inference 1
The
large number of
offspring must compete for
the finite resources.
Result - Most offspring die.
More Facts
Fact 4 - No two individuals in a
population are exactly alike.
Fact 5 - Variation is inheritable.
Inference 2
Those
individuals whose
inherited characteristics fit
them best to their environment
survive and reproduce.
Inference 3
Offspring
inherit the
favorable characteristics.
Populations shift over time as
the favorable characteristics
accumulate.
Nature
Determines
which
characteristics are favorable.
Determines who survives.
Result - “Natural Selection”
Natural Selection
in action
Artificial Selection
When
man determines the
characteristics that survive
and reproduce.
Result - the various breeds of
animals and plants we’ve
developed.
Ex - Mustard Plant
Original
Cultivars
Evolution Success
Measured By
Survival
Reproduction
Whoever
lives long enough
and has kids is the “winner”
in evolution.
Requirements
In
order for Natural Selection
to work, you must have:
Long
periods of time.
Variations within a population.
Subtleties of
Natural Selection
1. Populations are the units of
Evolution.
2. Only inherited characteristics
can evolve.
Comment
Acquired
characteristics may
allow a species to evolve
"outside" of Natural Selection.
Ex: culture, learning
Additional Signs
1. Biogeography
2. Fossils
3. Taxonomy
4. Comparative Anatomy
5. Comparative Embryology
6. Molecular Biology
Biogeography
The
geographical distribution
of species.
Problem:
Species
mixtures on islands
Marsupials in Australia
Evolution Viewpoint
Biogeographical
patterns
reflect descent from the
ancestors that colonized that
area.
Fossils
Relics
or impressions of
organisms from the past.
Problem:
Show
changes over time from
simple to complex.
Many fossils don't have
descendants.
Evolution
Viewpoint
Life
has
changed over
time.
Many species
failed to
survive and
became
extinct.
Comments
1. Fossilization is a rare event.
2. Only hard parts fossilize well.
3. Problem in finding fossils.
4. Interpretation.
5. Missing Links.
Taxonomy
Science
of Classification.
Main Categories
Kingdom
Phylum
Class
Order
Family
Genus
Species
or Division
Problem
- Why can life be
grouped this way?
Evolution Viewpoint Hierarchy reflects the
branching genealogy of the
tree of life.
Comparative Anatomy
Problems
1. Homologous Structures Common "building plan” with
divergent functions.
Comparative Anatomy
Problems
2. Vestigial
Organs Rudimentary
structures of
marginal, if
any, use.
Whale Legs
Human Example
Evolution Viewpoint
Remodeling
of ancestral
structures as their functions
or adaptations changed.
Comparative
Embryology
Problem
- closely related
organisms go through similar
stages in their embryonic
development.
Ex: Gill pouches in
vertebrates
Molecular Biology
Study
of Evolution at the
DNA or protein levels.
Problem - related species
have similar DNA sequences.
Evolution Viewpoint
Related
species share a
common ancestrial DNA.
The closer the relationship,
the more similar the DNA
sequences should be.
Summary
Darwin's
ideas now a "Theory”.
Predictions of a Theory are
tested by experiments and
observations.
Be familiar with the pre-Darwin
views of evolution.
Summary
Know
Darwin’s “facts” and
“inferences”.
Be able to discuss the
various evidences of
Darwinian evolution.