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Evolution
Evolution as Theory and Fact
• Confusion sometimes arises as to
whether Evolution is a theory or a fact.
Actually it is both!
• The theory of Evolution deals with how
Evolution happens. Our understanding
of this process is always changing.
• Evolution is also a fact as there is a
huge amount of indisputable evidence
for its occurrence.
Rodin’s “The Thinker”
LAMARCK
The lowest forms of life, such as bacteria, formed by
spontaneous generation from lifeless matter, and each
species would slowly change (i.e., evolve) into the next
higher species on the scale
Use-Disuse model-if an organism used a body part it
grew, if it didn’t, then it fell off
Whenever ADAPTATION was discovered, Lamarck
attributed it to the effects of use and disuse under
each individual's voluntary control
DARWIN'S IDEAS
Darwin's ideas were formulated principally
during the voyage of H.M.S. Beagle.
Darwin saw many tropical habitats much
richer in species than those he knew.
He noticed that the same habitat often
produced different species on different
continents: the savannahs (grasslands) of
East Africa and the pampas (grasslands) of
Argentina have almost no species in
common.
Darwin traveled around the world in
H.M.S. Beagle
Animals and Plants of South
America are vastly different
from those found in Africa or
Australia
South American Mammals-these species are very
different from the mammals found on other
continents, even where climates are similar
Darwin noticed that islands (like the
Galapagos) always had inhabitants whose
nearest relatives were on the nearest
continent
For example, the Galapagos Islands had
birds and plants related to those of South
America, while the Cape Verde Islands
(volcanic, geologically similar to the
Galapagos) had species related to those of
Africa and unlike those of the Galapagos
• Population-all the individuals of
a species that live together in
one place at one time
Galapagos Islands
Darwin’s Finches – land birds
Look at these pictures
First a few definitions
• Adaptation-changing of a species that
results in its being better suited to its
environment
DARWIN”S FINCHES FROM THE GALAPAGOS ISLAND
DARWIN”S FINCHES FROM THE GALAPAGOS ISLAND
BRANCHING DESCENT WITH MODIFICATION
Darwin's was not the first evolutionary theory, but it
was the first that emphasized BRANCHING descent
(in treelike patterns), which Darwin called "descent
with modification".
Descent with modification explained why
classifications should have "groups within groups":
families of related species, orders and classes made of
related families, etc.
THE PATTERN OF BRANCHING DESCENT
Methods for Species
• Isolation-when two populations of the same
species cannot breed with one another
• Extinct-when species disappear from the
planet forever
Charles Darwin (1809-1882)
Origin Of Species by Means of Natural Selection
2 major hypotheses
First major hypotheses, Branching
descent – species alive today came from
species that lived in earlier times and that
the lines of descent form a branched
pattern resembling a tree
Second major hypotheses, (natural
selection) – parents having genotypes
that favor survival and reproduction
leave more offspring, on average,
than parents having less favorable
genotypes for the same traits.
Natural Selection
Agents of selection can include predators,
diseases, environmental extremes, ability to obtain
food, and potential mates (of the opposite sex).
Natural Selection
Selection by potential mates is called SEXUAL
SELECTION.
FITNESS DEFINED: The relative number of
viable offspring left by each genotype.
Survival of the fittest
A GREAT DEAL OF
EVIDENCE SUPPORTS
DARWIN'S IDEAS
Evidence
• Earth is 4.5 Billion years old
• Organisms have inherited Earth for most of
its history
• All organisms living today evolved from
earlier, simpler life-forms
Evidence
• Paleontologists-scientists who study fossils
and can determine the age of fossils
– They have dated these fossils to get an accurate
evolutionary pattern
Evidence
• Vestigial structures-structures that are
evidence of an organisms evolutionary past,
but are not used today
– Appendix, Tail bone, gills in human embryoes
Evidence
• Homologous structures-structures that share
a common ancestry
– Limbs in mammals
How does this evolution occur?
• Gradualism-model of evolution in which
gradual change over a long period of time
leads to species formation
• Punctuated Equilibrium-Periods of
evolution marked by periods of little or no
change and then an explosion of change
Darwin's theory became accepted because it
explained the available evidence better than
any previous theory.
Natural selection can explain MIMICRY
while earlier theories could not: many species
survive because they resemble other,
unrelated species that predators avoid.
Selection by predators perpetuates the best
mimics and eliminates the less effective ones.
Industrial melanism among moths
demonstrates natural selection:
The frequency of dark-colored moths varies
geographically with levels of soot pollution.
Experiments with bird predators confirms
that predators eat the non-camouflaged
moths much more often than those which
resemble their background.
Industrial Melanism
Mimicry –Warning Coloration
Branching descent with modification explained the
facts of geographic distribution much better than
any previous theory
The theory also explained HOMOLOGIES
structures which resembled one another in their
construction among related species, despite
differences in adaptive use in many cases; earlier
theories could not explain homologies so well
Some homologies include embryonic characters;
others include functionless VESTIGIAL organs
Homology
Shared similarities are evidence
that the organisms in question share
a common ancestry
Homologies among mammalian forelimbs
The fossil record was poorly known in Darwin's
time, but fossils discovered since then have in most
cases fit well into branching patterns of descent
with modification.
The ages of fossils are determined by both relative
and absolute dating methods.
As an example: mollusks of the class Cephalopoda
(squids, octopus, extinct ammonites, etc.) all fit into
a pattern of branching descent, and their shared
adaptations and anatomical features are all
consistent with this pattern of descent.
REPRODUCTIVE ISOLATION
consists of all biological mechanisms
(not mere geographical separation)
that prevent the interbreeding of
natural populations.
REPRODUCTIVE ISOLATING
MECHANISMS can act either before or
after mating.
These mechanisms include isolation by
differences in ecology, differences in
mating seasons, differences in behavior,
differences which prevent sexual parts
from fitting together, or
incompatibilities that make gametes,
fertilized eggs, embryos, larvae, or adult
hybrids inviable or sterile.
HOW NEW SPECIES ORIGINATE
Most new species originate after a period of
geographic separation by an extrinsic barrier.
If the barrier lasts long enough for the
populations on either side to diverge, then one
or more reproductive isolating mechanisms
will result.
GEOGRAPHIC SPECIATION- THE EVOLUTION OF
REPRODUCTIVE ISOLATION DURING
GEOGRAPHIC ISOLATION
There is good evidence that evolution continues to
take place
Natural selection brings about seasonal
fluctuations in the characteristics of fruit flies and
Galapagos finches
Agricultural and industrial societies have greatly
changed the selective forces operating on human
populations
Evolution continues to take place wherever natural
selection occurs, meaning whenever mortality
differs according to genotype or phenotype
Discovery (1) Fixed species
Michelangelo’s fresco on the ceiling
of the Sistine Chapel
en.wikipedia.org/wiki/The_Creation_of_Adam
From Classical times until long after the Renaissance, species
were considered to be special creations, fixed for all time.
Discovery (2): Transmutation
• Around 1800, scientists began to
wonder whether species could
change or transmute.
• Lamarck thought that if an animal
acquired a characteristic during its
lifetime, it could pass it onto its
offspring.
• Hence giraffes got their long necks
through generations of straining to
Jean Baptiste de Lamarck reach high branches.
commons.wikimedia.org/wiki/Image:Jean-baptiste_lamarck2.jpg
en.wikipedia.org/wiki/Image:Giraffe_standing.jpg
Discovery (3): Fossils and Strata
http://en.wikipedia.org/wiki/
ImageWilliam_Smith.g.jpg
http://en.wikipedia.org/wiki/Image:
Geological_map_of_Great_Britain.jpg
http://en.wikipedia.org/wiki/Image:Smith_fossils2.jpg
William Smith, his geology map & some of his fossil specimens
At about the same time, geologists like William Smith were
mapping the rocks and fossils of Britain. He and others showed
that different species existed in the past compared with today.
Discovery (4): Darwin’s Voyage
• From 1831-1836, a
young naturalist called
Charles Darwin toured
the world in HMS
Beagle.
Voyage of the Beagle
en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpg
en.wikipedia.org/wiki/Image:HMS_Beagle_by_Conrad_Martens.jpg
• He was dazzled by the
amazing diversity of
life and started to
wonder how it might
have originated
Discovery (5): Survival of the Fittest
• In his Origin of Species,
published in 1859, Darwin
proposed how one species
might give rise to another.
Natural Selection
explains adaption
• Where food was limited,
competition meant that only
the fittest would survive.
• This would lead to the natural selection
of the best adapted individuals and
eventually the evolution of a new species.
en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg
Darwin in 1860
Discovery (6): Huxley v. Wilberforce
• Darwin’s idea of
Evolution by Natural
Selection was met with
huge controversy.
Bishop Wilberforce v. T. H. Huxley
• A famous debate in
1860 pitted Bishop
Wilberforce against
Darwin’s bulldog,
Thomas Henry Huxley.
• Evolutionists got the better of the debate, but few were convinced
by Darwin’s idea of Natural Selection.
www.bbc.co.uk/religion/galleries/spiritualhistory/images/9.jpg
Discovery (7): Genetics
Mendel and his peas
• From 1856-63, a monk called Gregor
Mendel cultivated 29,000 pea plants
to investigate how evolution worked
i.e., how characteristics were passed
down the generations.
• He figured out the basic principles of
genetics. He showed that offspring
received characteristics from both
parents, but only the dominant
characteristic trait was expressed.
Mendel’s work only came to light in
1900, long after his death
en.wikipedia.org/wiki/Image:Mendel.png
en.wikipedia.org/wiki/Image:Doperwt_rijserwt_peulen_Pisum_sativum.jpg
Discovery (8): Making Sense
• In the early 20th century, scientist started to
make sense of how evolution worked.
• Building on Mendel’s genetics, studies
showed how characteristics in a population
could be selected by environmental
pressures.
Julian Huxley
and the
Modern Synthesis
• This Modern Synthesis, as Julian Huxley
called it, brought Darwin’s Natural Selection
back to the centre of evolutionary theory.
en.wikipedia.org/wiki/Image:Hux-Oxon-72.jpg
Discovery (9): Opposition
• Despite the achieval of
scientific consensus on
evolution, some Christian
groups continued to
oppose the concept.
Outside the Scopes Trial
• In 1925, the teaching of
evolution was outlawed
in Tennessee, USA,
resulting in the infamous
Scopes Monkey Trial
www.templeton-cambridge.org/fellows/vedantam/publications/2006.02.05/eden_and_evolution/
Discussion: Should Creationism and Evolution
be given equal time in science lessons?
science.kukuchew.com/wp-content/uploads/
2008/01/stop_following_me_creationist.jpg
Mechanism (1): All in the Genes
• The genetic make-up of
an organism is known as
its genotype.
• An organism’s genotype
and the environment in
which it lives determines
its total characteristic traits
i.e. its phenotype.
Genotype
Phenotype
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG
Mechanism (2): DNA
• The double-helix
structure of DNA
was discovered
in 1953.
Watson and Crick and
their model of DNA
DNA
replication
www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpg
en.wikipedia.org/wiki/DNA
• This showed how
genetic information
is transferred from
one cell to another
almost without error.
Mechanism (3): Mutation
Types of mutation
• However, occasional
mutations or copying errors
can and do occur when
DNA is replicated.
• Mutations may be caused
by radiation, viruses, or
carcinogens.
Mutant fruitfly
• Mutations are rare and often have
damaging effects. Consequently organisms
have special enzymes whose job it is to
repair faulty DNA.
upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png
humansystemstherapeutics.com/bb.htm
Mechanism (4): Variation
• Nevertheless, some
mutations will persist and
increase genetic variation
within a population.
• Variants of a particular
gene are known as alleles.
For example, the one of
the genes for hair colour
comprises brown/blonde
alleles.
majorityrights.com/index.php/weblog/comments/racial_variation_in_so
me_parts_of_the_skull_involved_in_chewing/
Mechanism (5): Natural Selection
Selection of dark gene
• Mutant alleles spread through a
population by sexual reproduction.
• If an allele exerts a harmful effect,
it will reduce the ability of the
individual to reproduce and the
allele will probably be removed
from the population.
• In contrast, mutants with favorable
effects are preferentially passed on
en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg
Mechanism (6): Peppered Moth
Haldane and the peppered moth • The Peppered Moth is an
example of Natural Selection
in action discovered by Haldane


http://en.wikipedia.org/wiki/Image:Biston.betularia.7200.jpg
en.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpg
en.wikipedia.org/wiki/J._B._S._Haldane
• During the Industrial Revolution
the trees on which the moth
rested became soot-covered.
• This selected against the allele for pale
colour in the population (which were
poorly camouflaged from predators)
and selected for the dark colour allele.
Mechanism (7): Microevolution
• The dog is another example of how
selection can change the frequency
of alleles in a population.
• Dogs have been artificially selected
for certain characteristics for many
years, and different breeds have
different alleles.
Dogs are
wolves
• All breeds of dog belong to the same
species, Canis lupus (the wolf) so this
is an example of Microevolution as no
new species has resulted.
www.puppy-training-solutions.com/image-files/dog-breed-information.jpg
Mechanism (8): Macroevolution
• However, if two populations of a
species become isolated from
one another for tens of thousands
of years, genetic difference may
become marked.
• If the two populations can no-longer
interbreed, new species are born.
This is called Macroevolution.
Galapagos finches
• Darwin’s Galapagos finches are
an example of this process in action.
www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg
Mechanism (9): Speciation Today?
• The mosquito was introduced to
the London Underground during
its construction around 1900.
London Underground Mosquito
en.wikipedia.org/wiki/Image:Gb-lu-Angel-southbound.jpg
en.wikipedia.org/wiki/Culex
• It became infamous in the War
for attacking people sheltering
from the Blitz.
• Studies indicate several genetic
differences from its above-ground
ancestors. Interbreeding between
populations is difficult suggesting
that speciation may be occurring.
Activity
Natural Selection in the Peppered Moth
http://en.wikipedia.org/wiki/Image:Biston.betularia.7200.jpg
en.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpg
Evidence (1): Biochemistry
• The basic similarity of all living things suggests
that they evolved from a single common ancestor.
• As we have already seen, all living things pass
on information from generation to generation
using the DNA molecule.
• All living things also use a molecule
called ATP to carry
energy around the
DNA for
Information organism.
Transfer
en.wikipedia.org/wiki/Image:ATP-xtal-3D-sticks.png
ATP for
Energy
Transfer
Evidence (2): Similar Genes
HUMAN
CHIMPANZEE
GORILLA
CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCATGACTGTTGAACGA
CCAAGGTCACAACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
Genetic code of chimps and gorillas is almost identical to humans
• If evolution is true then we might also expect that closely
related organisms will be more similar to one another than more
distantly related organisms.
• Comparison of the human genetic code with that of other
organisms show that chimpanzees are nearly genetically identical
(differ by less than 1.2%) whereas the mouse differs by ≈15%.
Evidence (3): Comparative Anatomy
• Similar comparisons can be made
based on anatomical evidence.
• The skeleton of humans and
gorillas are very similar suggesting
they shared a recent common
ancestor, but very different from the
more distantly related
woodlouse…
Human and
Gorilla
yet all have a common
shared characteristic:
bilateral symmetry
Woodlouse
en.wikipedia.org/wiki/Image:Primatenskelett-drawing.jpg
Evidence (4): Homology
The pentadactyl limb
is ancestral to all
vertebrates…
but modified for different uses
en.wikipedia.org/wiki/Image:Evolution_pl.png
Evidence (5): Vestigial Structures
• As evolution progresses, some
structures get side-lined as they
are not longer of use. These
are known as vestigial structures.
• The coccyx is a much reduced
version of an ancestral tail, which
was formerly adapted to aid
balance and climbing.
The coccyx is a vestigial tail • Another vestigial structure in
humans is the appendix.
en.wikipedia.org/wiki/Image:Illu_vertebral_column.jpg
Evidence (6): Fossil Record
http://en.wikipedia.org/wiki/Geologic_time_scale
© World Health Org.
en.wikipedia.org/wiki/Image:Eopraptor_sketch5.png
© NASA
origins
bacteria complex cells dinosaurs
humans
The fossil record shows a sequence from simple bacteria to
more complicated organisms through time and provides the most
compelling evidence for evolution.
Evidence (7): Transitional fossils
• Many fossils show a clear
transition from one species,
or group, to another.
• Archaeopteryx was found
in Germany in 1861. It
share many characteristics
with both dinosaurs and
birds.
Archaeopteryx
en.wikipedia.org/wiki/Image:Archaeopteryx_lithographica_paris.JPG
• It provides good evidence
that birds arose from
dinosaur ancestors
Evidence (8): Geography
• Geographic spread of
Marsupials organisms also tells of
their past evolution.
• Marsupials occur in
two populations today
in the Americas and
Australia.
• This shows the group
evolved before the
continents drifted apart
evolution.berkeley.edu/evosite/lines/IVCexperiments.shtml
en.wikipedia.org/wiki/Image:Kangaroo_and_joey03.jpg
Evidence (9): Antibiotic resistance
Staphylococcus
• We are all familiar with
the way that certain
bacteria can become
resistant to antibiotics
• This is an example of natural selection in
action. The antibiotic acts as an
environmental pressure. It weeds out
those bacteria with low resistance and
only those with high resistance survive
to reproduce.
http://en.wikipedia.org/wiki/Image:Antibiotic_resistance.svg
en.wikipedia.org/wiki/Image:Staphylococcus_aureus%2C_50%2C000x%2C_USDA%2C_ARS%2C_EMU.jpg
Evolution
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG
commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg