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Photo by “davemee” flickr
creative commons
"nothing in biology makes sense
except in the light of evolution”
~Theodosius Dobzhansky (19001975)
Which of these applies to scientific
theory?
•
•
•
•
•
•
•
A. Theories include observations
B. Theories are hunches scientists have
C. Theories can include personal beliefs or opinions
D. Theories have been tested many times
E. Theories are incomplete, temporary ideas
F. A theory never changes
G. Theories are inferred explanations, strongly supported by
evidence
• H. A scientific law has been proven and a theory has not.
• I. Theories are used to make predictions
• J. Laws are more important to science than theories
Answers A, D, G, I best describe scientific theories
• In science, theories are
statements or models that
have been tested and
confirmed many times.
• I will read a paragraph and
you take what you want from
it.
In science, the term "Theory" does
not express doubt.
• They explain a wide variety of data
and observations
• They can be used to make
predictions
• They are not absolute, can be
changed as new evidence is found
• Why do so many different animals
have the same structures, the arm
bones in a human are the same
bones as a flipper in a whale?
• Why is the sequence of DNA very similar
in some groups of organisms but not in
others?
• Why do the embryos of animals look very
similar at an early stage?
Photo courtesy of Swamibu, Flickr Creative Commons
• Charles Darwin
developed the
THEORY OF
EVOLUTION BY
NATURAL
SELECTION
• which explained how
organisms changed
over time (ADAPTED)
• Lamarke's Theory of
Acquired Characteristics
• Some thought that you would
gain or lose features if you
overused or didn't use them,
• PROVEN TO BE WRONG!
Example:
A giraffe acquired its long neck because
its ancestor stretched higher and higher into the
trees to reach leaves, and that the animal’s
increasingly lengthened neck was passed on to
its offspring.
Photo courtesy of ucumari, creative
commons, flickr
• Darwin’s views were influenced by fossils, the relics
or impressions of organisms from the past, mineralized
in sedimentary rocks.
– Sedimentary rocks form when mud and sand settle to the
bottom of seas, lakes, and marshes.
– New layers of sediment cover older ones, creating layers of
rock called strata.
– Fossils within layers show that a succession of organisms
have populated Earth throughout time.
Fig. 22.2
Fig. 22.4
• Darwin was a naturalist (what we today call
biologists)
• He traveled the world and made observations and
sketches of many species
• His most famous travels were aboard the H.M.S.
Beagle where he traveled to the Galapagos Islands
Marine Iguana, photo courtesy of mtchm, flickr
creative commons
Blue-footed booby, photo courtesy of stirwise,
flickr creative commons
Finch, photo courtesy of stirwise, flickr,
creative commons
Giant tortoise, photo courtesy of Planetgordon,
flickr creative commons
• Darwin noted that there
existed many finches on
the islands, but while they
had similarities, each was
adapted to eating a
particular type of island
food
• He concluded that the
finches all came from one
ancestral species and
evolved into many new
species
Cactus finch, photo courtesy of zrim,
flickr creative commons
• Darwin published this
work to explain the
variety of species
that exist on the
planet
• He proposed the
“Theory of Evolution
by Natural Selection”
• Natural selection
provided a mechanism for
evolutionary change in
populations.
1. Variation exists among individuals in a
species.
2. Individuals will compete for resources (food,
mates, and space)
3. Competition would lead to the death of some
individuals while others would survive
4. Individuals that had advantageous variations
are more likely to survive and reproduce.
This process came to be
known as Natural Selection
The favorable variations are
called Adaptations
Photo courtesy of
digitalART2, flickr
creative commons
• Natural selection acts on the phenotype, or the
observable characteristics of an organism, such
that individuals with favorable phenotypes are
more likely to survive and reproduce than those
with less favorable phenotypes.
• The phenotype's genetic basis, the genotype
associated with the favorable phenotype, will
increase in frequency over the following
generations. Over time, this process may result in
adaptations that specialize organisms for
particular ecological niches and may eventually
result in the emergence of new species.
• Darwin’s main ideas can be
summarized in three points.
• Natural selection is differential success in
reproduction (unequal ability of individuals to
survive and reproduce).
• Natural selection occurs through an interaction
between the environment and the variability
inherent among the individual organisms
making up a population.
• The product of natural selection is the
adaptation of populations of organisms to their
environment.
• While natural selection involves
interactions between individual organisms
and their environment, it is populations,
not individuals that evolve.
• Populations are defined as a group of
interbreeding individuals of a single
species that share a common geographic
area.
• Say in a species of blob….there exists
blobs of all shapes and sizes (variation)
Blobs eat the little purple organisms that live
underground and on the surface.
During a particularly hot year, food became less
abundant (competition), blobs that had the ability to
dig into the soil to get food had a better chance of
survival.
Many blobs died that year…….
The ones that survived mated and passed their genes
to the next generation. (reproduction)
The next generation had move blobs with the pointed
noses. That is NATURAL SELECTION.
1. Variation
2. Competition
3. Survival
4. Reproduction
Evolution is when organisms change over time. So, modern
organisms descended from ancient ones
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
Fossil Evidence
• Shows numbers extinct animals
• Shows similarities between extinct animals and animals that are
alive today
• The earth’s layers show a time scale of species and when they
appeared on earth (and when they died out)
Dinosaurs have always fascinated us, movies such as
Jurassic Park capitalize on that fascination.
How do we know what dinosaurs
looked like?
We create a picture based on the
bones we find (fossils) and use
modern reptiles to guess at their
texture and skin color.
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 tell a story…
Primate Fossils
Australopithecus
sapien
Homo erectus
Homo
Relative vs.
Absolute
Dating
Fossil
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
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
• Homologous structures – these are parts of the
body that are similar, but have different functions
ex. The flippers of
whales, and the wings
of birds
All forelimbs of
vertebrates have the
same pattern of bones
• Common ancestry
Homologous
Structures
modifies
homologous
structures
Adaptive Radiation Modifies homologous structures
Morphology
But don’t be fooled by these…
 Analogous
 look
structures
similar
 on
the outside
 same
function
How is a bird different structure & development
like a bug?
 on
the inside
 different
origin
 no evolutionary relationship
Solving a similar problem with a similar solution
In your notes….
• In one sentence, write your answer to the following
question…..
– What is the difference between homologous and
analogous structures?
• Vestigial Organs – these are organs or parts that
seem to have no function
Whales have pelvic bones that do not attach to legs
•
Vestigial
organs
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!
3. Molecular record
• Comparing DNA & protein structure
– everyone uses the same genetic code!
• DNA
 compare
common genes
 compare
common
proteins
number of amino acids
different from human
hemoglobin
Human
Macaque
Dog Bird
Frog
Lamprey
8
32 45
67
125
0 10 20 30 40 50 60 70 80 90 100 110 120
• Biochemistry and DNA
When comparing the DNA of one species to another, more
similarities are found in species that are more closely
related.
Lion photo credit: ucumari Tiger photo credit: digitalART2
DNA
Embryological Development
Embryos of different species develop in almost identical
ways.
Human fetus at 8 weeks
Embryology
Convergent Evolution
These animals have evolved similar adaptations
for obtaining food because they occupy similar
niches. What can you infer about their
phylogeny from their geographic locations?
Punctuated Equilibrium
“instead of a slow, continuous movement,
evolution tends to be characterized by long
periods of virtual standstill ("equilibrium"),
"punctuated" by episodes of very fast
development of new forms”
The "punctuated equilibrium" theory of Niles
Eldredge and Stephen Jay Gould was
proposed as a criticism of the traditional
Darwinian theory of evolution…what is it
called?
Convergent Evolution
• Species exposed to the
same selective pressure in
different parts of the world
tend to develop the same
adaptations
• Even though they may be
completely unrelated
• e.g. the placental wolf and
the marsupial thylacine or
Tasmanian wolf
© 2008 Paul Billiet ODWS
Thylacine Thylacinus cynocephalus
Wolf Canis lupus
Convergent evolution led to mimicry
• Why do these pairs look so similar?
Monarch male = poisonous
fly
bee
Viceroy male = edible
moth
bee
Divergent Evolution
• Populations of a species that are separated and
evolve under different selective pressures
develop different adaptations as they diverge
• They are usually geographically separated so that
there is a barrier to the mixing of genes
© 2008 Paul Billiet ODWS
Direct observation of species change
1.Bacteria become resistant to antibiotics
2.Wolves were bred over many generations to
become dogs (artificial selection) • and then bred
further to create a variety of breeds
3. Micro Evolution: Natural selection
in action: the evolution of
insecticide-resistance
•New insecticides are effective, killing 99% of the insects.
• The few survivors resist the chemical attack.
• Only these resistant individuals reproduce, passing on their
resistance.
• In each generation the percentage of insecticide-resistant
individuals increases.
• In general, natural selection operates not to create
variation, but to edit existing variation.
Fig. 22.12
• For patients treated with the drug 3TC, which
interferes with genome replication in HIV, 3TCresistant strains become 100% of the population of
HIV in just a few weeks.
Fig. 22.13
Endosymbiotic Theory