Chapter 22 Descent with Modification: A Darwinian View of Life
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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
Read Chapter 22 (Hillis – 15)
Chapter 20 – today
Exam 2 – March 19
AP Exam enrollment???
Chapter 22 – Wed. 3/20
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
Field Study – measured the beak size of all birds in a population over several years.
Result – drought and food competition changed beak size.
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.
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