Download The Theory of Evolution

Darwin’s Theory of Evolution
Ch. 15
Evolution
• Evolution means
change over time
• A scientific theory is
NOT just a belief, it is
a well-supported
tested explanation.
Darwin
• In 1831 Darwin sets
sail on the HMS
Beagle.
• In 1844 he writes his
theory on the origin of
species.
• In 1858, Darwin and
Wallace publish their
theories on evolution.
• Evolution means
change over time.
History of Darwin’s Studies
• Darwin went on an aroundthe-world trip on the HMS •
Beagle and traveled to the
Galapagos Islands.
• He particularly liked and
observed the finches. He
also observed the tortoises
on different islands.
• He observed each different
group had its own niche.
He studied 13 different
species and saw how
they adapted to their
environment.
Fossils
• A fossil is the
preserved remains or
imprints of ancient
organisms.
• Someone who studies
fossils is called a
paleontologist.
• Fossils are found in
sedimentary rock
formed when sand and
silt settle to the bottom
of water.
• Not all animals turn
are fossilized, why?
• Do you think we have
a complete fossil
record?
Determining ages of Fossils
• Relative dating– Looks at the layer of
the earth they are
found.
– The oldest fossils will
be deeper.
• Radioactive dating
– Determined by
remaining radioactive
isotopes the fossil
contains.
Radioactive Dating
• What is an isotope?
• Scientists estimate the
age of fossils by
analyzing the isotope
in the rock around
fossils.
• Some isotopes are
radioactive and
undergo radioactive
decay.
Half-life
• During radioactive
decay, the isotope
gives off particles and
energy changing its
identity to a different
element.
• It occurs during a
constant rate, called its
half life.
• Radioactive potassium
(40K) decays to produce
argon gas. Its half-life is
1.3 billion years.
• The half-life of an element
is the time it takes for half
of the atoms in a sample to
undergo radioactive decay.
Types of radioactive dating
• Potassium-Argon dating is
used for rocks that are
suspected billions of years
old.
• In older rocks the ratio of
Argon to 40K will be higher
than in younger rocks.
Why?
• Because in the younger
rocks the K has not yet
started to decay to Argon.
• Carbon dating: 2 types
• 14C:12C
– Radioactive 14C
– Non-radioactive 12C,
most common
Ways to determine ages of
fossils.
• K-Ar dating
• Radiocarbon dating
– Scientists looks at the age of
rocks and fossils that are
found near them are assumed
to be the same age.
Solve:
8g of 14C in a fossil and 16g in
living org. How old?
3g 14C in a fossil and 12g 12C. .
– Living org. absorb12C and 14C.
The ratio is constant.
– When org. dies it no longer
absorbs C. 14C (radioactive)
begins to decay and decreases
while 12C (non-radioactive)
stays the same.
– 14C half-life every 5600 years.
Look at ratio of 14C to 12C and
compare to living org.
Tracking Changes
• According to
evolutionary theory,
all life originated from
a common unicellular
ancestor through
natural selection.
• Scientists use
radioactive dating to
calculate fossil’s age.
• The phylogeny (or
evolutionary tree), is
not linear, it branches
and stops and some of
it is incomplete.
Time line of Evolution
• Explanations of the
origin of diversity go
back to the Greek’s
2000ya. They
theorized that an
organisms form is
related to it’s function
• In 1769 Charles
Bonnet observed that
fossils do not resemble
modern organisms and
theorizes they are
from a previous era.
An Ancient, Changing Earth
• In 1785 James Hutton • Charles Lyell agreed
proposed the Earth is
and wrote a book in
shaped by geological
1833 the explained the
forces that took place
shaping of Earth’s
over extremely long
geological features.
periods of time. He
• He gave his book to
estimated the earth is
Darwin before Darwin
millions, not
set sail.
thousands of years old.
Popular Belief
• Prior to the studies of Charles Darwin, the most
widespread belief was that all known species were
created at the same time and remained unchanged
throughout history.
• Some scientists at the time believed that features an
individual acquired during a lifetime could be passed
onto its offspring, and the species could gradually
change to fit an environment better.
2.1
Lamark
• In 1809 Jean-Baptiste
•
Lamarke hypothesized that
“simple” organisms emerge
spontaneously and evolve to
greater “complexity”.
• Lamark’s hypothesis about
acquired characteristics was
disproved by Weisman, who
concluded that changes in an
individual during a lifetime
do not affect its offspring.
3 principles to his theory:
1. Organisms constantly strive
to improve themselves.
2. Most used body structures
develop and unused waste
away.
3. A structure is modified by
use or disuse, the
modification is inherited to
the offspring. (Inheritance of
acquired characteristics.)
Darwin’s Arguments
• Darwin argued that only biologically inherited
characteristics were advantageous in surviving and
reproducing. The offspring would also inherit and
pass on those advantages, and over generations the
aggregation of these inherited advantages would
lead to new species.
2.2
Population Growth
• In 1798 Malthus
reasoned that if the
human population
continued to grow
unchecked, sooner or
later there would be
insufficient living
space and food for
everyone.
• Do you agree of
disagree with
Malthus?
Population Control
• Darwin read Malthus’
work reasoned that
there is always
competition for food,
water and space in the
environment. The
individuals that
survive the
competition can then
reproduce.
Returning Home
• He found that any domesticated
• When he returned
plant or animal bred to
home he studied and
accentuate desirable
read other people’s
characteristics is the result of
materials about
artificial selection. (Natural
geological changes.
provides variation and humans
• He also studied the
select the variations useful)
selective breeding of
domestic animals and • Many veggies we eat today
came from the wild mustard
crops.
plant through artificial
selection.
Origin of Species
• Darwin’s book, published in 1859, was a quick
success. It came from the clear and
understandable argument that natural selection
and selective breeding of animals was in wide use
at the time. There was a massive array of
biological and fossil evidence to support the
argument.
• Selective breeding: breeding of organisms to
produce certain desired traits in their offspring.
2.3
Support From Others
• After the publication of Origin of Species,
biological evolution was supported by the
rediscovery of the genetics experiments of Gregor
Mendel, by the identification of genes and how they
are sorted in reproduction, and by the discovery that
the genetic code found in DNA is the same for
almost all organisms.
• Darwin came to his conclusions prior to Mendel’s
work.
2.4
Variation
• A species consists of
interbreeding
populations organisms
that produce healthy
offspring.
• Within a species there
is much variation or
differences between
members of a
population.
• Give an example of
variation among a
species.
Variation
• Variation can be
dramatic or subtle.
• Examples of how
organisms may vary:
–
–
–
–
–
–
Fur color
Shape of teeth
Size
Markings
Biochemically
Eye color
Other things that cause Variation
Inherited variation:
1. Mutation
2. Recombination
• Most mutations are either
neutral or harmful,
sometimes they may
increase the chance for
survival, esp. when the
environment is changing.
• Ie. Silver colored red fox
in a snowy environment.
1.23b Altered genes may be passed on to every cell that
develops from it. This may help, harm, or have little or no
effect on the offspring’s success in the environment.
Biodiversity
• In communities populations
of organisms live to
• There are between 5
together, interact, and often
and 30 million
compete for natural
different species.
resources. These
• 99% of all organisms
communities include a
that ever lived are now
collection of niches. The
extinct.
variety and abundance of
species that make up a
biological community is
called biodiversity.
Biodiversity is Good
• The great diversity of species increases the
chance that at least some living things will
survive in the face of the large changes in the
environment.
• Genetic recombination allows for a greater
diversity.
1.46
Niches
• Through adaptation,
populations often
become suited to a
specific niche.
• Niche- habitat and the
role of a population
plays in that habitat.
• It includes:
– Where organisms live
– What and how they eat
– How they raise their
offspring
– What their predators are
– Space
– Light
– Moisture
– Temperature
Adaptation
• An adaptation is an
inherited trait that
increases a
population’s chance of
survival and
reproduction in a
particular
environment.
• What are some ways
that you know animals
have adapted to their
environment?
• The ability of an
individual to survive
and reproduce in its
specific environment
is fitness.
Survival of the Fittest
• Individuals that are best suited to an environment
(adaptations that enable fitness) survive and
reproduce most successfully.
• Over time, natural selection results in changes in
the inherited characteristics of a population. These
changes increase a species fitness in its
environment.
Natural Selection Tutorial
Natural Selection
•
4 Main Points.
1.
2.
3.
4.
5.
1.31
There is variation with a
population.
Some variations are
favorable.
Not all young produced in
each generation survive.
Individuals that survive
and reproduce are those
with favorable variations.
Descent with
Modification
Ostriches are the fasted birds on land due to
favorable traits such as long, powerful legs.
Natural Selection
• Natural Selection leads to organisms that are well
suited in particular environments.
• It provides a scientific explanation for the history of
life on Earth as depicted in the fossil record and
similarities evident within the diversity of existing
organisms.
1.32
Descent with Modification
• Over time, natural
selection produces
organisms that have
different structure,
establish different
niches, or occupy
different habitats. As
a result, they look
different from their
ancestors.
• What do you think the
common ancestor to
tigers, panthers and
cheetahs looked like?
• Common descent- all
living and extinct
organisms were
derived from a
common ancestor.
Evolution Tutorials
Evolution Lab
Evolution in Action
Structures
• Homologous Structures- • Vestigial Structures- inherited,
traits that are similar in
but reduced in size and often
different species because
unused.
the species share a
Ie. Pythons have hip and leg
common ancestor.
bones.
Ie. Arm, fin and wing
may have evolved from Analogous structures- those that
the forelimb of a common are similar in function, but are
not inherited from a common
vertebrate.
ancestor.
Ie. Insect and Bird Wings
Exploring Evolution
DNA history
• Scientists rely on
embryology and
biochemistry to
understand evolution.
• Gill pouches in all
vertebrates.
• Embryology is the
study of the early
stages of an organisms
development.
• Biochemists study and
compare chemicals
found in living things.
Evidence of Evolution
• Darwin argued
that living things
have been
evolving on
Earth for
millions of years.
• 1. Fossil Record- layers of earth
• 2 Geographical distribution of
living species- similar animals
in different locations were the
product of different lines of
evolutionary descent.
• 3. Homologous structures
• 4. Similarities in early
development (embryology)
Evolution of Populations
Ch. 16
And
Ch. 17 Part 2
Genetic Variation
• The more genetic
variation within a
population, the
better chance it
has to survive.
• Why?
• 2 sources
– Mutations
– Genetic recombination
during meiosis
Crossing over
Population Genetics
In genetic terms, evolution
is any change in the
allele frequency (relative
frequency) of alleles in a
population
• Gene pool- all the
combined genetic
material of all of the
members of a given
population.
• Allele frequency- the •
number of each allele is a
fraction of all of the
genes for a particular
trait. (pg. 394)
Sexual reproduction can
produce many different
phenotypes, but it does
not change the relative
frequency of alleles in a
population. Think of
deck of cards.
1.36
Single Gene and Polygenic Traits
• Single gene trait is
controlled by one gene
–
–
–
–
–
Widows peak
Freckles
Dimples
Roll tongue
Taste PTC
• Polygenic traits are
controlled by many
genes.
– Body stature
– Eye color
– Height
Natural Selection on Single Gene
Traits
• Natural Selection on
Single Gene traits can
lead to changes in allele
frequencies…evolution.
• Organisms of one
color, may produce
fewer offspring than
organisms of other
colors.
• See figure 16-5 pg.
397
Natural Selection on Polygenic
Traits
• Natural selection can
affect the distributions
of phenotypes in 3
ways.
1. Directional selection
2. Disruptive selection
3. Stabilizing selection
Directional and Disruptive
Selection
• Directional Selection
occurs when a change
in the environment
favors an extreme
phenotype.
• What is a phenotype
and what are some
examples?
• Ie. Peppered moth
• Disruptive selection
occurs when an
environmental change
makes it unfavorable
to have a medium
phenotype. You need
an extreme one.
Note: Berkley did an experiment and found the conditions
for the moth example, wasn’t 100% the way perceived.
Testing Natural Selection in Nature
• Rosemary and Peter Grant visited the Galapagos
Islands and did not see the different finches
competing or eating different foods. During the
rainy season, there is plenty of food and finches
are able to eat anything. In the dry season
drought, food becomes scarce and differences in
beak size can mean the difference between life and
death. What time of selection is this?
• Directional
Directional Selection Example
Directional selection favors those individuals who have
extreme variations in traits within a population. A useful
example can be found in the breeding of the greyhound dog.
Early breeders were interested in dog with the greatest speed.
They carefully selected from a group of hounds those who ran
the fastest. From their offspring, the greyhound breeders again
selected those dogs who ran the fastest. By continuing this
selection for those dogs who ran faster than most of the hound
dog population, they gradually produced a dog who could run
up to 64km/h (40mph).
The greyhound was originally used to hunt the fastest of game,
fox and deer. Their bred dates to Egypt in 3BC.
Hardy Weinberg Principle
• If a population is not
evolving, the allele
frequencies in the
population remain
stable.
• This constant state of
allele frequency is
called genetic
equilibrium.
• It states that, under
specific conditions, allele
frequencies in a
population remain
constant from generation
to generation. If specific
conditions are not met,
genetic equilibrium in
interrupted and the
population may evolve.
Maintaining Genetic Equilibrium
• 5 conditions:
1. No natural selection
2. Random mating
3. No migration
4. No significant mutations.
5. Very large population
Hardy-Weinberg Tutorial
Hardy-Weinberg equations for population with 2
alleles at a locus (but only works if one assumes
random mating):
p+q=1
Generation 1
Frequency
A allele
Generation 2
2
p
Frequency
of AA
genotype
Frequency of
a allele
+ 2 pq +
Frequency of
Aa genotype
2
q
=1
Frequency
of aa
genotype
Genetic Drift
• Genetic Drift is the random
change in allele frequencies in
a population due to chance
events, such as natural
disasters or migration. (Would
genetic drift have a greater
impact on smaller or larger
populations?)
Ex. Florida Panther- hunted-less
genetic variation- Texas
cougars introduced
1.36
• “Bottlenecking” is
when genetic drift
occurs after a random
population reducing
event.
• The more variation,
the easier it is to
survive because they
can adapt better.
Founder effect
• Allele freq. change as a result of the
migration of a small subgroup of
population.
• Will the new population become different or
more like the parent population?
• Due to chance
• Ex: Hawaiian Fruit Flies
Genetic Drift
Let’s show how you get the allele frequencies.
An example is the Cheetah.
Speciation
• Speciation is the
evolution of one or
more species from a
single ancestor
species.
• It can occur when
members of a population
become isolated from each
other. (possibly from
earthquakes.)
• Once two populations are
reproductively isolated,
they are considered
separate species.
Allopatric Speciation
• Aka. Geographical
Isolation
• Physical barrier ( continental
split, rise in sea level, formation
of mountain range, advance of
glacier, change in habitiat)
prevents gene flow between
populations of a species
– Archipelago hotbed of speciation
Allopatric Speciation
Allopatric Speciation in the Grand Canyon
Behavioral Isolation
• Two populations
are capable of
interbreeding,
but have
differences in
courtship rituals
or other
reproductive
strategies.
Temporal Isolation
• Two or more species
reproduce at different
times.
• Orchid releasing
pollens on different
days, they can’t
pollinate each other.
Speciation in Darwin’s Finches
• Speciation in the
Galapagos finches
occurred by:
• 1. Founding of a new
population.
• Geographic isolation
• Changes in new
population’s gene pool
• Reproductive isolation
• Ecological
competition
2 major extinctions
• Cretaceous- more than
half of all existing
species wiped out.
(Dino’s)
• 65 mya
• Permian- reduced the
number of species by
90%.
• 250 mya during
Pangea- less water
habitat.
Evolution does not occur in a set
direction
• Evolution builds on
what already exists, so
the more variety there
is, the more there can
be in the future.
• However, evolution
does not necessitate
long-term progress in
a set direction.
Rate of Evolution
• Gradualism- theory that • Punctuated equilibriumnew species evolve as the
theory that populations
genomes of two
remain genetically stable for
populations differentiate
long period of time,
over enormous spans of
interrupted by brief periods
time.
of repaid genetic change.
(Small genetic changes
• Rapid genetic changes in a
occur slowly within a
population can result in the
population.)
evolution of new species.
Graduated vs. Punctual
Mechanisms of Evolution
• Divergent Evolutionwhen isolated populations
of a species evolve
independently. It occurs
when geographic barriers
separate population
members or when a small
group leaves an original
population.
• Ex: polar bears and
brown bears
• Convergent Evolutionoccurs when natural
selection has produced
analogous adaptations in
response to similar
environment between
different species.
Ie. Maned Wolf and
Serval Cat
Eat same, legs same,
ears same.
Coevolution
• Species that interact
closely often adapt to
one another in a
process called
coevolution.
• What does the prefix
co- mean?
• Ex:
– Predatory birds and
mimicry of butterflies
– Parasites and hosts
– Plant-eating animals
and the plants they eat
– Plants and the animals
that pollinate them.
Adaptive Radiation
Adaptive Radiation is the
evolution of many diversely
adapted species from one
common ancestor. It usually
occurs on an isolated island.
ie. Finches that Darwin
studied all came from
common ancestor, but had
different beaks for the kind of
food they ate.
What differences do you see between the tree finches and ground
finches? Why?
Patterns of Evolution
Parent
Species
Which is adaptive radiation, divergent, convergent, and
parallel evolution?
Why is understanding evolution
important?
•
•
•
•
Drug resistance to viruses and bacteria
Pesticide resistance
Selective Breeding
Others?
• How do each of these effect you?
Evolution Review
• Click on the following link and choose your
text book. Use the links to review the
material and take the self-tests.
• Ch. 15,16,17 Review