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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
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.
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.
Result
No evolution.
Created the viewpoint that all
species could be identified
and named (Taxonomy).
A major factor in the
Linnaeus classification
system.
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
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.
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.
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.
Result
Darwin's training and travel
opportunities allowed him to
formulate and support his
ideas on Natural Selection.
Result - July 1, 1858
Dual presentation of the
Wallace-Darwin ideas to the
Linnaean Society of London.
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.
“The Origin of Species”
Documented the occurrence
of evolution.
Suggested that the
mechanism for evolution was
Natural Selection.
Observation 3
All species are
capable of
producing
more offspring
than their
environment
can support.
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”
Artificial Selection
When man determines the
characteristics that survive
and reproduce.
Result - the various breeds of
animals and plants we’ve
developed.
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.
Comments
1. Fossilization is a rare event.
2. Only hard parts fossilize well.
3. Problem in finding fossils.
4. Interpretation.
5. Missing Links.
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.
Recommended