Chapter 22:
Descent with
Modification - A
Darwinian View of
Life
Essential Knowledge
1.a.1 – Natural selection is a major
mechanism of evolution (22.2).
1.a.4 – Biological evolution is
supported by scientific evidence
from many disciplines, including
mathematics (22.3).
Evolution
The processes that have transformed
life on earth from its beginnings
Change in genetic make-up over time
Gradual appearance of biological diversity
Illustrates science as a PROCESS
Evolutionary
Adaptation
An accumulation of inherited
characteristics that enhance an
organisms ability to survive and
reproduce
Involves populations – group of
animals of same species that live
in same geographic area
Pre-Darwinian Views
1. Greeks
2. Fixed
3. Catastrophism
4. Hutton and Lyell
5. Lamarck
Greek Philosophers
1. Plato - Organisms are already
perfectly adapted to their
environment
2. Aristotle - Organisms arranged on
a “scale of life” from simple to
complex
Fixed,
unchanging
Ladder of Life
Result: Greek
No evolution
Life is already perfect and doesn’t
need to change
All the rungs on life's "ladder" are
already occupied.
Fixed Species
The creator had designed each and
every species for a particular
purpose.
Coincides with Old Testament
Says Earth is only5-6,000
yrs old (according
to the Bible)
Result: Fixed
Species
 No Evolution!
 Created the viewpoint that all species
could be identified and named
(Taxonomy).
 A major factor in the Linnaeus
classification system
 Similarities showed pattern of
creationism (not an evolutionary
pattern)
Catastrophism
 Georges Cuvier
(1769-1832).
 Attempted to relate
fossils to current life
 Paleontology started
 Noticed: Deeper
fossils were less
similar
Catastrophism Idea
 Fossils were the remains of species lost due
to catastrophe
 No new species originated; species could
only be lost over time
 Each rock/strata boundary represented a
catastrophe
 Catastrophe destroyed all/many species
 Created a mass extinction
 Result – No evolution!
James Hutton
Geologist
Related living organisms
and
their changes to changes in the
Earth
1795 - Gradualism
Profound change is the cumulative
product of slow, but continuous
process
Result: Gradualism
Changes on the Earth were
gradual, not catastrophic.
Gradual mechanisms change
living organisms (and Earth)
Charles Lyell
Geologist
1797 - 1875.
Incorporated
Hutton’s gradualism
into a theory called
Uniformitarianism.
Uniformitarianism idea
Geological processes have
operated at the same rate over
the Earth’s history
These processes are STILL
occurring today
More comprehensive theory
(involved past AND present)
Result:
Uniformitarianism
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 over time
Jean Baptiste
Lamarck
Published
theory in 1809.
Theory - Life
changed from
simple to
complex over
time
Lamarck
Fossils were the remains of past
life forms
Used fossils to create of descent
Evolution did occur.
His two mechanisms were
incorrect
Mechanisms
1. Use and Disuse Body parts used to survive
become larger and stronger
Body parts not used to survive
deteriorate.
Ex: giraffe (neck was constantly
stretched to reach leaves)
Mechanisms
2. Inheritance of Acquired
Characteristics
Modifications acquired by use/disuse
were passed on to offspring
Ex: muscular arms
(you work out and
therefore your children
will be muscular)
Problem w/ Lamarck
He had no prior knowledge of
genetics (hadn’t been “discovered”
yet)
Acquired traits are not transmitted
offspring
Lamarck claimed animals have an
innate drive to become more
complex (not better adapted!)
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
Problem: timing (too fast!)
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).
Was a poor student
Quit medical school (to become
clergy man and ship naturalist)
Voyage of the Beagle
Result: Voyage
Became interested in geographic
distribution of species (why certain
animals live where they do?)
Visited: Brazilian jungles, Galapagos
islands, Argentina, Antarctica, Andes
Mtns
Allowed him to formulate and support his
ideas on Natural Selection
Galapagos Finches
Beaks and behaviors have
adapted to specific foods
available on specific islands
Island Tortoises
Neck lengths have adapted to
foods on specific islands
Marine Iguanas
Adapted swimming/walking
adaptations to be successful
both in water and on land
Alfred Wallace 1858
 Wrote paper on
natural slection
 Ideas were identical
to Darwin's.
 Waited to publish
(wrote to Darwin w/
ideas)
Result - July 1, 1858
 Dual presentation of
the Wallace-Darwin
ideas to the
Linnaean Society of
London.
 Lyell presented
 1859 – Darwin
published (solo) the
“Origin of Species”
Comment
Darwin best remembered for the
theory because of his
overwhelming evidence and
because he published 1st!
Wallace could have received credit
for his ideas (but he idolized Darwin
and wanted him to get the
attention)
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
Most
branches are dead ends!
99% of all species are extinct
“The Origin of
Species”
Documented the occurrence of
evolution
Suggested that the mechanism for
evolution was Natural Selection.
Conclusion: Biological diversity
was/is the product of evolution
“The Origin of
Species”
Focused on diversity of organisms
Includes: geographic distribution,
adaptations, origins
Two points:
1) Ancestral descendants
2) Natural selection is mechanism for
evolution
The Theory of
Evolution
Based upon 5 major
facts/observations
Helps to devise 3 evolutionary
inferences
Evolution: The Facts:
Fact 1 - All
species
reproduce
themselves
Until resources
limit this growth
The Facts, cont:
Fact 2 –
Most populations are normally
stable in size
Fact 3 –
Natural Resources are limited
(finite).
Inference 1
Use Facts 1, 2, 3
The large number of offspring
must compete for the limited
resources
Result - Most offspring will die!
More Facts
Fact 4 –
No two individuals in a population
are exactly alike
Fact 5 –
Variation is inherited
Inference 2
Use Facts 4, 5
Those individuals whose inherited
characteristics fit them best to
their environment will survive and
reproduce!
Inference 3
Use Facts 4, 5
Offspring inherit the favorable
characteristics
Populations shift over time as
the favorable characteristics
accumulate
Thomas Malthus
Demographer
(geographic
distribution and
population growth)
Helped Darwin to
develop these
inferences
Nature
Nature: Food, shelter, disasters,
climate
Determines which characteristics are
favorable
Favors some, while filtering others
Determines who will survive!
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.
Genetic engineering!
Evolution Success
Measured By:
Survival rate
Reproductive rate (success)
Whoever lives long enough and
has kids is the “winner” in
evolution.
Requirements for
Natural Selection
In order for Natural Selection to
work, you must have:
Long periods of time
Variations within a population
Subgroups of Natural
Selection
1. Populations are the units of
Evolution (NOT individuals)
2. Only inherited characteristics can
evolve (traits passed from parent to
offspring)
3. Natural selection is always
operating (based upon
environmental factors)
Comment
Some acquired characteristics
may allow a species to evolve
"outside" of natural selection
Ex: culture, learning, diet,
exposure to mutagens
Nature vs. nurture
Visible Signs of
Evolution
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
Biogeography
 Closely/Evolutionarily-related species tend
to be found in the same geographic region
 However, the same niches (in differing
regions of the world) are usually occupied
by species that may have evolved similar
adaptations – but are DIFFERENT species
 Ex: sugar glider and flying squirrel
**Both have adapted similar
adaptations (skin flaps) but are
NOT closely related to each
other. They have evolved this
adaptation independently
** Islands often contain ENDEMIC
species (species that are found NO
WHERE ELSE in the world!)
**Why? Islands are a perfect example
of how geography influences evolution
Evolution Viewpoint
Biogeographical patterns reflect
descent from the ancestors that
colonized the 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: Fossils
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.
Using various
characteristics –
group organisms
by like
characteristics
Main Categories
Domain
Kingdom
Phylum or Division
Class
Order
Family
Genus
Species
Comparative
Anatomy
1. Homologous
Structures Common
"building plan”
with divergent
functions
Mammal forelimbs
Comparative
Anatomy
Whale Legs
2. Vestigial
Organs Rudimentary
structures of
marginal, if any,
use.
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
All animals go
through these
stages of
development!!
Evolution Viewpoint
Ontogeny is a replay of Phylogeny.
(Development reflects descent)
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
ancestral DNA. The closer the
relationship, the more similar
the DNA sequences should be.
Summary
 Recognize viewpoints of evolution preceding
Darwin, and identify their main points and
characteristics.
 Identify the assumptions, inferences and
outcomes of Darwin's Theory of Natural
Selection.
 Recognize the signs of the process of evolution
through the mechanism of natural selection.