Transcript Ch. 15.2 Evidence ofEvolution

Ch. 15.2 Evidence of Evolution
Ch. 15.3
Objectives:
• Describe how fossils provide evidence of evolution
• Discuss morphological evidence of evolution
• Explain how biochemistry provides evidence of
evolution
Evidence supporting evolution
• Fossil record
– shows change over time
• Anatomical record
– comparing body structures
• homology & vestigial structures
• embryology & development
• Molecular record
– comparing protein & DNA sequences
• Artificial selection
– human caused evolution
1. Fossil record
• Layers of rock contain fossils
– new layers cover older ones
• creates a record over time
– fossils show a series of organisms have lived on
Earth
• over a long period of time
Fossils shape ideas about evolution
Fossils: direct or indirect remains of organisms
preserved in media such as sedimentary rock, amber,
ice, or tar
Ammonite casts
–Fossilized organic
matter in a leaf
–Fossilized organic
matter in a leaf
Ice Man”
Fossils tell a story…
the Earth is old
Life is old
Life on Earth has changed
Fossils tell a story…
the Earth is old
Life is old
Life on Earth has changed
What has the fossil record shown us?
• The creatures alive today haven’t
OBSERVATION
always been around
Different species
lived in the past
We found the fossil — no joke!
Land Mammal
?
?
?
Complete series
of transitional
fossils
Someone’s idea of a joke!
But the joke’s on them!!
Ocean Mammal
?
Evolution from sea to land
• 2006 fossil discovery of early tetrapod
– 4 limbs
• Missing link from sea to land animals
2. Anatomical record
Animals with different
structures on the surface
But when you look under the
skin…
It tells an evolutionary story of
common ancestors
Compare the bones
• The same bones under the skin
– limbs that perform different functions are built
from the same bones
Homologous structures
• Structures that come from the same origin
• homo- = same
• -logous = information
• Forelimbs of human, cats, whales, & bats
– same structure
• on the inside
– same development in embryo
– different functions
• on the outside
– evidence of common ancestor
But don’t be fooled by these…
 Analogous structures

look similar
 on the outside
same function
 different structure & development

 on the inside
How is a bird

like a bug?
different origin
 no evolutionary relationship
Solving a similar problem with a similar solution
Analogous structures
 Dolphins: aquatic mammal
 Fish: aquatic vertebrate
both adapted to
life in the sea
 not closely related

Watch the tail!
Vestigial organs structure—a body structure in a presentday organism that no longer serves its original purpose, but was
probably useful to an ancestor.
• Hind leg bones on whale fossils
Why would whales have
pelvis & leg bones if they
were always sea
creatures?
Because they
used to
walk on land!
Comparative embryology
• Development of embryo tells an evolutionary
story
– similar structures during development
all vertebrate embryos have a “gill
pouch” at one stage of development
3. Molecular record
• Comparing DNA & protein structure
– everyone uses the same genetic code!
• DNA
Human
Macaque
Dog Bird
Frog
32 45
67
Lamprey
 compare common genes
 compare common proteins
number of amino acids different from
human hemoglobin
8
125
0 10 20 30 40 50 60 70 80 90 100 110 120
Building “family” trees
Closely related species are branches on the tree — coming
from a common ancestor
4. Artificial selection
• How do we know natural selection can
change a population?
– we can recreate a similar process
– “evolution by human selection”
“descendants” of wild mustard
Selective Breeding
Humans create the
change over time
“descendants” of the wolf
Artificial Selection gone bad!
• Unexpected
consequences of
artificial selection
Pesticide resistance
Antibiotic resistance
Insecticide resistance
• Spray the field, but…
– insecticide didn’t
kill all individuals
• variation
– resistant survivors
reproduce
– resistance is inherited
– insecticide becomes less &
less effective
Adaptations: Evidence for Evolution
• an adaptation is any variation that aids an organism’s
chances of survival in its environment.
• According to Darwin’s theory, adaptations in species
develop over many generations
• Learning about adaptations in mole-rats can help you
understand how natural selection has affected them.
Structural adaptations arise over time
• camouflage, an
adaptation that enables
species to blend with their
surroundings.
• Because wellcamouflaged organisms
are not easily found by
predators, they survive to
reproduce.
Structural adaptations arise over time
• Mimicry is a structural adaptation that enables one
species to resemble another species.
• Predators may learn quickly to avoid any organism with
their general appearance
Physiological adaptations can develop rapidly
• In general, most structural adaptations develop over millions of years.
• However, there are some adaptations that evolve much more rapidly.
•
The evolution of insecticide resistance is an example of natural selection in action
Convergent evolution
• 3 groups with wings
– Does this mean they have a
recent common ancestor?
They just
came up
with the
NO!
same answer!
Flight evolved 3
separate times —
evolving similar
solutions to similar
“problems”
Convergent evolution led to mimicry
• Why do these pairs look so similar?
Monarch male
Viceroy male
poisonous
edible
Which is the moth
bee?
fly vs.vs.
thethe
bee?
fly
bee
moth
bee
Natural selection acts on variations
• There are three different types of natural
selection that act on variation: stabilizing,
directional, and disruptive.
Natural selection acts on variations
• Stabilizing selection is a natural selection
that favors average individuals in a
population.
Selection for
average size
spiders
Normal
variation
Natural selection acts on variations
• Directional selection occurs when natural
selection favors one of the extreme
variations of a trait.
Normal
variation
Natural selection acts on variations
• In disruptive selection, individuals with
either extreme of a trait’s variation are
selected for.
Selection for
light limpets
Normal variation
Selection for
dark limpets
The Evolution of Species
• Significant changes in the gene pool
could lead to the evolution of a new
species over time.
• The evolution of new species, a process called
speciation occurs when members of similar
populations no longer interbreed to
produce fertile offspring within their
natural environment.
The Evolution of Species
• Geographic isolation occurs whenever a
physical barrier divides a population.
• A new species can evolve when a population
has been geographically isolated.
Reproductive isolation can result in speciation
• Reproductive isolation occurs when formerly
interbreeding organisms can no longer mate
and produce fertile offspring
• A change in chromosome numbers-
polyploidy can lead to speciation
Speciation rates
• Gradualism is the idea that
species originate through a
gradual change of adaptations
• Some evidence from the fossil
record supports gradualism.
• In 1972, Niles Eldredge and
Stephen J. Gould proposed a
different hypothesis known as
punctuated equilibrium.
• This hypothesis argues that
speciation occurs
relatively quickly, in rapid
bursts, with long
periods
of genetic equilibrium in
between.