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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.
Theory vs theory
Theory
Hypothesis
supported
repeatedly by
data
Makes testable
predictions
theory
Layman’s and
TV use of the
word
Confused with
hypothesis in
Science
Examples of Theory
Cell
Theory
Big Bang Theory
Atomic Theory
Theory of Gravity
Theory of Evolution
Evolution
Has
itself "evolved" or changed
over time.
Illustrates “Science as a
Process”.
Students should be able to give
the main points of several views.
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.
Thomas Malthus
Essay
on human population
growth in 1798.
Disease, famine, homelessness,
and war are inescapable because
human populations grow faster
than food supplies.
Darwin read Malthus.
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.
Homework
Chapter 22 (Hillis – 15)
Chapter 20 – today
Exam 2 – March 19
AP Exam enrollment???
Chapter 22 – Wed. 3/20
Read
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.
Observations:
Observation 1 – Members of a
population often vary greatly in
their traits.
.
Observation 2
Traits
are inherited from
parents to offspring.
Observation 3
All species are
capable of
producing
more offspring
than their
environment
can support.
Observation 4
Owing
to lack of food or
other resources, many of
these offspring do not
survive.
Inference 1
Individuals
whose inherited
traits give them a higher
probability of surviving and
reproducing in a given
environment tend to leave
more offspring than other
individuals.
Inference 2
This
unequal ability of
individuals to survive and
reproduce will lead to the
accumulation of favorable
traits in the population over
generations.
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:
Variations
within a population.
Long periods of time (according
to Darwin).
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
Evidences for Evolution
Direct
observation of
evolutionary changes.
Fossils
Homology
Convergent Evolution
Biogeography
Molecular
Direct Observations
Color
patterns in guppies
Drug resistant HIV
Beak size in Birds
PitX1 gene
Others
Color Pattern in Guppies
Field
Experiment (see text for full
details)
Changed the selection pressure
on male guppies
Result – color pattern change in
15 generations (22 months).
HIV Drug Resistance
Drug
resistance strains
selected for by treatments
Result – resistant strains
became 100% dominant in 4-5
weeks.
Beak Size
Study – measured the
beak size of all birds in a
population over several
years.
Result – drought and food
competition changed beak
size.
Field
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.
Homology
Homologous
Structures Common
"building
plan” with
divergent
functions.
Mammal forelimbs
Problems
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.
Homology in Embryos
Problem
- closely related
organisms go through similar
stages in their embryonic
development.
Ex: Gill pouches in
vertebrates
Evolution Viewpoint
Ontogeny
is a replay of
Phylogeny.
(Development reflects descent)
Development reflects inheritance
of common control genes.
Convergent Evolution
Unrelated
organisms show
similar adaptations.
Cause – lived in a similar
environment with similar
selection pressures.
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.
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 “observations”
and “inferences”.
Be able to discuss the various
evidences of Darwinian
evolution.