Transcript Unit 15.2 Evidence of Evolution PowerPoint

Evidence supporting evolution
• Fossil record
– shows change over time
• Anatomical record
– comparing body structures
• Homologous & vestigial structures
• embryology & development
• Molecular record
– comparing protein & DNA sequences
• Artificial selection
– human caused evolution
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: 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
What has the fossil record shown us?
• The creatures alive today haven’t always been around
OBSERVATION
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
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 an insect?
 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 present-day
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
Molecular (chemical) record
• Comparing DNA & protein structure
– everyone uses the same genetic code!
• Same 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
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
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
fast 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”
Natural selection acts on variations
• There are three different types of natural
selection that act on variation: stabilizing,
directional, and disruptive (diversifying).
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.
Speciation rates
• This hypothesis argues
that speciation occurs
relatively quickly, in
rapid bursts, with long
periods of genetic
equilibrium in
between.