Transcript Chapter 22 Notes

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.
 “Nothing
in Biology Makes Sense
Except in the Light of Evolution”Theodosius Dobzhansky
Note:
Evolution does NOT
say anything about how life
originated
It DOES describe how life
changes through time.
Early Ideas on Life’s
Diversity
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.
Carolus Linnaeus
(1707-1778)
 Classified life according to genus and
species.
 Thought the diversity in life was fixed from
life’s origins
 Each lifeform was perfectly designed from
the beginning for its role
 Still use his classification system today

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.
The lower the stratum, the more dissimilar life is to today’s life
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.
First to propose a
mechanism for evolution
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.
On
twitter: @cdarwin
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.
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.
https://www.youtube.com/watch
?v=0jFGNQScRNY
Evolution Success
Measured By
Survival
Reproduction
Whoever
lives long enough
and has kids is the “winner”
in evolution.
Subtleties of Evolution
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
Drug
resistant HIV
Beak size in Birds
Many Others
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
Homologysimilarities
resulting from
common
ancestors
Mammal forelimbs
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.
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.
Convergent Evolution
Unrelated
organisms show
similar adaptations.
Cause – lived in a similar
environment with similar
selection pressures.
Analogous Structures-similar function, but the structures are NOT from a
common ancestor
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.
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.