Download Evolution Unit Notes

Introduction to
Evolution
What is evolution?
A basic definition of evolution…
“…evolution can be precisely defined as any
change in the frequency of alleles within a
gene pool from one generation to the next."
- Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974
So what does the definition
mean?
• Evolution is a change in the number of times
specific genes that code for specific
characteristics occur within an interbreeding
population
• Individuals don’t evolve, populations do
• There is no implied “improvement” in
evolution
Genetic Variation and
Evolution
Evolution: changes through time
1. Species accumulate difference
2. Descendants differ from their
ancestors
3. New species arise from existing
ones
A brief history of Charles Darwin
Born on February 12, 1809 in
England.
From 1831 to 1836 Darwin
served as naturalist aboard
the H.M.S. Beagle on a British
science expedition around the
world.
A brief history of Charles Darwin
He observed variation in
related or similar species of
plants and animals that were
geographically isolated from
each other.
These observations were the
basis for his ideas.
Natural Selection
Darwin knew nothing of
genes
What he did have were
two observations
From these he made
inferences that provided
the motive force for
evolution
Natural Selection
Observation 1: Organisms generally have
more offspring than can survive to
adulthood.
Observation 2: Offspring are not identical.
There is variation in their appearance,
size, and other characteristics.
Natural Selection
Inference: Those organisms that are better
adapted to their environment have a greater
likelihood of surviving to adulthood and passing
these characteristics on to their offspring.
Survival of the “fittest.”
Survival of the “fittest.”
Darwin’s theory
for how long
necks evolved in
giraffes
Natural selection: mechanism of
evolutionary change
Individuals have specific inherited characteristics
They produce more surviving offspring
The population includes more individuals with
these specific characteristics
The population evolves and is better adapted to its
present environment
Fitness in Biology
Fitness: A phenotype with greater fitness
usually increases in frequency
– Fitness is a combination of:
– Survival: how long does an organism live
– Mating success: how often it mates
– Number of offspring per mating that survive
Hardy–Weinberg principle
Genotype frequencies in a population
remain constant or are in equilibrium from
generation to generation…unless specific
disturbing influences are introduced.
Hardy–Weinberg principle
Those disturbing influences include
1. new mutations
2. gene flow
3. genetic drift
4. selection
5. non-random mating
In genetics terms, evolution is any
change in the relative frequency of
alleles in a gene pool of a population.
Points to Make:
1. Gene pool -- all genes (alleles) that
are present in a population.
2. Frequency -- the number of times
that allele occurs in a gene pool.
3. Evolution is studied and understood
at the population level NOT species
level.
a. Populations evolve not
individuals.
Why do allele frequencies change?
5. Non-Random Mating
AKA selective mating
examples:
• Inbreeding or mating
between relatives
• Assortative matingchoosing mates with
similar phenotypes
• Competition
All living things share a
common ancestor.
We can draw a Tree of
Life to show how every
species is related.
•Evolution is a theory and a fact.
• 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”
• 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.
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG
• 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.
Types of mutation
•Occasional mutations or
copying errors can occur
when DNA is replicated.
• Mutations may be caused
by radiation, viruses, or
carcinogens.
Mutant fruit fly
• Mutations are rare and often have
damaging effects.
upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png
humansystemstherapeutics.com/bb.htm
• Some mutations will persist
and increase genetic
variation within a population.
• Variants of a particular
gene are known as alleles.
For example, one of
the genes for hair color
comprises brown/blonde
alleles.
majorityrights.com/index.
php/weblog/comments/racial_variation_in_some_parts_of_the_skull_in
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 passed on
☒
☑
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
• The Peppered Moth is an example of
Natural Selection in action
• 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 color allele.
• 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
• 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
• 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
• Studies indicate several genetic
differences from its above-ground
ancestors. Interbreeding between
populations is difficult suggesting
that speciation may be occurring.
• The basic similarity of all living things suggests
that they evolved from a single common ancestor.
• All living things pass on information from generation
to generation using the DNA.
DNA for
Information
Transfer
• All living things also use a molecule
called ATP to carry
energy around the
organism.
en.wikipedia.org/wiki/Image:ATP-xtal-3D-sticks.png
ATP for
Energy
Transfer
HUMAN
CHIMPANZEE
GORILLA
CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCA TGACTGTTGAACGA
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%.
• 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
en.wikipedia.org/wiki/Image:Primatenskelett-drawing.jpg
Woodlouse
The pentadactyl limb
is ancestral to all
vertebrates…
but modified for different uses
en.wikipedia.org/wiki/Image:Evolution_pl.png
• 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
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 tim.
• 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
Marsupials
• Geographic spread of
organisms also tells of
their past evolution.
• Marsupials occur in
two populations today
in the Americas and
Australia.
evolution.berkeley.edu/evosite/lines/IVCexperiments.shtml
en.wikipedia.org/wiki/Image:Kangaroo_and_joey03.jpg
• This shows the group
evolved before the
continents drifted apart
Staphylococcus
• 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