Transcript Evidence of Change Through Time

Darwin proposed his theory of evolution to explain life on earth
and he proposed natural selection as the process of evolution.
This theory is one of the most well accepted theories in science
so, why is that…
What is the evidence to support evolution?
420 mill yr old
sea star fossil
How do we use that evidence to understand evolutionary
history and relationships between organisms.
Evidence of Change Through Time
I. Fossils
-any trace of an organism that lived in the past
-e.x. bones, branches, shells, tracks, impressions & dung
Fig 24.3
Evidence of Change Through Time
http://videos.howstuffworks.com/hsw/12698-windows-into-the-past-how-fossils-form-video.htm
http://www.pbs.org/wgbh/evolution/library/04/3/l_043_01.html
Evidence of Change Through Time
I. How do fossils form?
Organism (that makes it way to the ocean) dies and sinks to
bottom. If not scattered by scavengers, gets covered by sediment
Once safely buried in sediment, soft parts decompose and then
hard parts become replaced by dissolved minerals.
Fish pics: http://www.discoveringfossils.co.uk/whatisafossil.htm
Evidence of Change Through Time
I. How do fossils form?
What’s left is a cast of an organism that becomes compressed
into rock by pressure of sediments settling on top
When sediments are raised and exposed by erosion (wind, rain)
then fossils accessible to paleontologists.
Evidence of Change Through Time
The layer of rock in which the fossil is found and
radiometric dating (of rock) can tell us how old
the fossil is
Evidence of Change Through Time
Learning from fossils is not an
easy process
http://www.pbs.org/wgbh/nova/beta/evolution/b
ecoming-human-part-1.html
http://www.pbs.org/wgbh/nova/beta/evolution/building-fossils-faces.html
Evidence of Change Through Time
I. Fossils: Crazy Example
Joesephoartigasia monesi (freakishly big rat)
Lived 4 mya in South America
Fossil discovered in Uruguay 1989, studied and reported in Jan 08
Est 1700 to 3000 lbs, preyed on saber-tooth cats
(cbsnews.com)
Evidence of Change Through Time
Misconception: “Gaps in the fossil record disprove evolution.”
Response: The fact that some transitional fossils are not
preserved does not disprove evolution. Evolutionary biologists do
not expect that all transitional forms will be found and realize that
many species leave no fossils at all.
Evidence of Change Through Time
I. Limitations of Fossils
•Fossilization is an extremely low probability event
and it is nonrandom meaning not all organisms are
equally likely to fossilize.
•For instance any species with hard body parts such
as shells or teeth or coating of pollen may fossilize,
whereas soft-bodied like earthworm usually won’t
500,000 million yr old
Jellyfish fossil (rare).
•Also requires that the organism make it’s way to the water
for fossilization process to work
Evidence of Change Through Time
II. Extinction
Fossils that were unlike any structures from any known
animal or plant
Of all the species
that ever lived
~ _98_ %
are extinct.
Dodo
late 1600s
Human activity
Irish Elk
11,000 ya
Glaciation
Evidence of Change Through Time
III. Transitional Forms:
Fossil species with traits that are intermediate between
those of older and younger species.
•Archaeoptreryx lithographica: earliest bird fossil (1891)
• Transitional form between dinosaurs and birds
• 150 million year ago
Evidence of Change Through Time
III. Transitional Forms
• Transitional Form between fish and tetrapods (land animals)
• Discovered in Ellesmere Island, CA
• 375 million years old
Recent Discovery (2004): Tiktaalik
Lived about 12 million yrs
before 1st tetrapod which is
~363 million years old
Tiktaalik significant b/c shows
earliest appearance of
tetrapod features- features
that are not seen in their
fish ancestors.
Evidence of Change Through Time
ribs
Fins
Fin skeleton resemble bones
of forearm, shoulder, elbow
and wrist
http://tiktaalik.uchicago.edu/meetTik.html
Evidence of Change Through Time
Evidence of Change Through Time
IV. Vestigial traits
reduced or incompletely
developed structure with
no function, reduced function or
completely different function but is
structurally similar to
functioning structures in closely
related species
Evidence that Species are Related
I.
Geographical Relationships- closely related species
often live in same geographical area
Common ancestor but over time,
mockingbirds diversified into several
distinct species on different island
groups
Fig 24.6
Evidence that Species are Related
II. Homology: Similarity that exists in species
descended from a common ancestor
Three types:
A. Genetic
B. Developmental
C. Structural
A. Genetic Homology
Evidence that Species are Related
Significant similarity in DNA, RNA or proteins in species
descended from a common ancestor.
Expect more DNA changes over longer period of time
1.2%
difference
1.6%
difference
50% difference
0.1% difference
Evidence that Species are Related
A. Genetic Homology
•Nearly identical sequence
in genes for determining
eye development in humans
and Drosophila
•Yet humans and flies have
completely different eyes
•Humans and and flies descended
from common ancestor that had this
gene for formation of a simple lightgathering organ, structure diverged,
but same gene responsible for
location of eyes
Evidence that Species are Related
B. Developmental Homology
Similarity in embryonic traits in species descended from a
common ancestor
Patterns of early embryological development don’t change
readily so early patterns of animals are still similar even
when organisms look very different as adults
Movie
Fig 24.8
Evidence that Species are Related
B. Developmental Homology:
Why are developmental stages so preserved?
Think of the early stages as the foundation of a house.
*
**
**
* ***
***
A mutation in DNA (remove a few bricks from the
foundation) is likely to be more detrimental
than if a brick is removed from the top of the house
Evidence that Species are Related
C. Structural Homology
Similarities in adult morphology
All vertebrate limbs modified from same #
and arrangement of bones
Fig 24.9
Evidence that Species are Related
aquatic
terrestrial
Why is all of this important?
Fossils, vestigial traits, transitional forms, geographical
relationships, structural, genetic and developmental homologies
•Provide evidence that organisms are all related.
Gives us clues about which ones are more closely
related and how along ago they diverged
•Provide evidence that organisms change over time
Gives us clues about how long it took for certain
changes to occur and why they occurred.
For example:
“Did land animals evolve from fish?”
*Fish have a gill gene that forms gills, which fish need. Land
animals have the same gene causing their formation during
early development even though land animals have no use for
gills. So if they didn’t inherit this gene from fish- why would
they have it? The change over time: gills not needed in land
animals, having them in adulthood was selected against by
natural selection
The primary type of evidence mentioned
above:
Developmental Homology
For example:
“Did land animals evolve from fish?”
Discovery of tiktaalik demonstrates there was at once time a
fish-like species that evolved tetrapod features demonstrating
how this evolution could have occurred.
This organism lived about 12 million years before tetrapods
appeared telling us how long this evolution took.
Evolution from fish to tetrapod not an instant event so without an
intermediate form, we couldn’t understand how that evolution
occurred even though we have genetic, develop. and structural
homology data to support that they are related.
The primary type of evidence mentioned above:
Transitional Forms and Fossils
3. Which of the following is the most
compelling support for Darwin’s theory of
evolution?
1. There are fossils of once living
organisms.
2. Fossils are found throughout geologic
strata.
3. Evidence shows that some fossilized
species are extinct.
4. Evidence shows that extinctions
occurred throughout history.
4. Which of the following could be used as
evidence of descent from a common
ancestor?
1. Species of tortoise living in close
proximity are more similar than tortoise
species living far apart.
2. Genes for limb formation have almost
identical sequences in salamanders and
chimpanzees.
3. Antibiotics can cure the same diseases in
rabbits and humans.
4. All of the above could be used as
evidence.
5. Which of the following is a true
statement?
1. An individual with an adaptation is said to
have evolved.
2. An individual who is naturally selected has
more offspring than an unselected individual.
3. An individual that needs an adaptation to
survive is more likely to evolve it.
4. Over time organisms will become