Download Darwin`s Theory of Evolution by Means of natural selection

Darwin’s
Theory of
Evolution
Who was Charles Darwin?
• Originally a student of theology
• Then became a naturalist
• In 1831, took ship and sailed around the
world
• During his travels, Darwin made numerous
observations and collected evidence that
led him to propose a revolutionary
hypothesis about the way life changes over
time
Darwin’s Voyage
Darwin’s Observations
• Patterns of diversity
– HUGE amount of diversity among living
things
– Diversity in
• Traits
• Offspring production
• Habitat
Darwin’s Observations
• Darwin often stopped to collect fossils
•Preserved remains of ancient
organisms
•Some looked like modern organisms,
some clearly did not
•Where did these organisms fit it? Why
had so many species disappeared?
The Galapagos Islands
• Located west of South America
• Islands were close but had very
different climates
• Very fascinated by both the tortoises
and the finches on these islands
– Tremendous variety
Common ancestor? Changed to fit
environment?
The ride back home
• Darwin’s return provided a lot of
time for reflective thought
• Darwin observed that the
characteristics of many animals and
plants varied noticeably among the
different islands of the Galápagos.
– Critical point
The ride back home
• Darwin came up with a possibility
– Could the animals on the different
islands have once been the same
species?
• Was that even possible??
Ideas that shaped Darwin’s
Ideas
• Darwin built upon the work of those
before him
• Other scientists built upon his work
• But…
– Many people were shocked by his
ideas and he did not receive a lot of
initial support
Evolutionary Roadblocks
• Ideas in Darwin’s
time
1. Earth was only
a few thousand
years old
• Later shown to
be billions of
years old
Evolutionary Roadblocks
• Ideas in Darwin’s
time
2. Both the planet
and its
organisms were
immutable
(could not
change)
• Planet is always
changing…and
the life on it
Evolutionary Roadblocks
• Ideas in Darwin’s time
3. Any strange geologic features were the
results of infrequent catastrophes that
humans rarely witnessed
•
Simply not true
People who influenced
Darwin
• Scientists had a large influence on
Darwin
1. James Hutton
2. Charles Lyell
3. Jean Baptiste Lamarck
• …And an economist
4. Thomas Malthus
1. James Hutton
• Layers of rock are built
very slowly
• Geological forces
shaped Earth’s
features (mountains
and valleys)
• Took MILLIONS of years
• Earth is not a few
thousand years old
2. Charles Lyell
• Wrote Principles of
Geology
• Stressed that
processes that
shaped Earth
millions of years
ago are the same
processes that do
so today
3. Jean-Baptiste Lamarck
• Did realize that
organisms change
over time
• Published his work
the year Darwin
was born (1809)
Lamarck’s Proposition
• Lamarck proposed that by selective
use or disuse of organs, organisms
acquired or lost certain traits during
their lifetime. These traits could then
be passed on to their offspring. Over
time, this process led to change in a
species.
– Had three supporting principles
A. Tendency Towards
Perfection
• All organisms have a tendency
towards perfection and complexity
• Acquired features that helped them
live more successfully in their
environments
– EX: Giraffe has an urge to be tall, and
tries to do so
B. Use and Disuse
• Organisms could alter the size and
shape of their organs by using them
in new ways
• If an organ was not used, it would
eventually disappear
– EX: By trying to be tall, giraffe stretches
its neck out
C. Inheritance of
Acquired Traits
• If an organism altered its body
structure during its lifetime, then it
would pass the new trait to its
offspring
– EX: If the giraffe stretched its neck and
it got longer, its babies would have
longer necks
4. Thomas Malthus
• Looked at population
– Notice that babies were being born
faster than people died
– Malthus reasoned that if the human
population continued to grow
unchecked, sooner or later there would
be insufficient living space and food for
everyone.
4. Thomas Malthus
• Looked at population
– Thought that war, famine, and disease
were the only things that keep the
population in check
• Darwin realized this was true for every
organism, and not just humans
• Most offspring die
– WHY do some die and some survive?
4. Thomas Malthus
• Food supply is
linear
• Population
growth is
exponential
• Problem?
Evidence supporting
Darwin’s Ideas
1.
2.
3.
4.
5.
6.
Fossil Evidence
Homologous Structures
Analogous Structures
Vestigial Structures
Comparative Embryology
Biochemical evidence
1. Fossil Evidence
• Fossil evidence shows that living
things have been evolving on earth
for millions of years.
• Also showed that the geographic
distribution of organisms lines up
with the movement of the earth’s
crusts & that newer (more modern)
forms of fossilized organisms are
found in the upper layers of rock
2. Homologous Structures
• Structures that have similar form but
different functions
– Bones of our forearm, the front flipper
of a whale, the wing of a bat & legs of
a turtle.
• Could all four limbed animals with
backbones have descended with
modification from a common
ancestor?
3. Analogous Structures
• Structures that have same function
but different structure/structure
– Fly and Bird wing
• Was environment similar so it made
sense to have this feature?
4. Vestigial Structures
• Structures which no longer have a
function to the organism.
– Our appendix, hair, coccyx, wisdom
teeth
• These vestiges had a useful function
at one time but since they are no
longer of an adaptive use to the
organisms, they have become
reduced with time.
5. Comparative Embryology
• Compares structures of developing
organisms (embryos)
• Structures found in embryos that have no
function/use or are not present in adults
– Early stages of development of many animals
with backbones are very similar
• Common ancestor!
6. Biochemical evidence
•
Not used by Darwin but in use today!
–
–
Using modern biotechnology, examine
the amino acids (proteins) and genes
(DNA) of organisms.
Similar organisms will have more in
common. The more closely related they
are, the more recently they descended
from a common ancestor
On the Origin of Species
• Darwin’s book
• Hesitant to publish
– Alfred Russel
Wallace—incentive
• Never talks about
origin of life but
how new species
come to be
Darwin’s Theory of Evolution by
Means of natural selection
1.
Variation
– In a population, there are variations in
different traits
2. Overpopulation
– In nature, more organisms are born than
can survive
3. Competition and Struggle for existence
– There are not enough resources for all
organisms!
– Certain species have natural
advantages
Darwin’s Theory of Evolution by
Means of natural selection
4. Survival of the fittest / Natural Selection
– You’ve got the correct combination of
advantageous traits (adaptations)?
•
–
You survive! Try to have babies and pass on
those stellar genes/traits!
You do not have the correct variations
and adaptations?
•
You die!...that’s it.
5. Species change over time
–
–
–
Due to natural selection
S L O W process
New forms / species arise; others disappear
Natural Selection
Comparing:
Lamarck and Darwin
L
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A
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C
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D
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Comparing:
Lamarck and Darwin
What was Darwin missing?
• Darwin published his work in
1836
– Did not have all pieces to the
puzzle
1. What was the source of variation?
2. How are variations passed down
from generation to generation?
What was Darwin missing?
• Mendel did not publish his work
until 1900
• Watson and Crick did not publish
their work until 1953
• We can now answer the questions
Darwin couldn’t using genetics,
molecular biology, and
evolutionary theory experiments
Sources of Genetic
Variation
1. Mutation – may increase, decrease or have
no effect on the organism’s fitness
2. Gene shuffling – during meiosis & fertilization,
genes get shuffled
3. Crossing over – new combinations result
during prophase I of meiosis
Why does it all change?
• The environment changes!
– Adaptive radiation—the idea that as organisms
spread out to a new environment, they will acquire
changes that allow them to better survive in the
environment
• Radiate—spread out
• Adapt—change
– Best seen with Darwin’s finches on the
Galapagos islands
Adaptive Radiation
• Darwin’s Finches – small brown birds
– Ancestral finches evolved to adapt to
open niches on the various Galapagos
Islands.
– Some evolved a shorter, fat beak for
cracking large seeds, some have a smaller,
pointier beak for opening small seed, while
others have a long pointed beak for
getting into creases in bark for insects
Adaptive Radiation
Darwin’s Finches
Evolutionary paths
• Based on the
environment…
1. …species can become
more different
– DIVERGENT evolution
– Results in speciation
– Leads to homologous
structures
– Idea of adaptive radiation
Evolutionary paths
• Based on the
environment…
2. …species can become
more similar
– CONVERGENT evolution
– Leads to analogous
structures
Genetic Drift and the
Founder Effect
• Genetic Drift
– In a small population (isolated one),
a particular allele may occur more
frequently even though it doesn’t
lead to the fitness of the
population, it is just there
• Founder Effect
– Is the change in gene frequency as
a result of the movement of a small
group of a population.
The
founder
effect
CAUSES
genetic
drift.
Sicilian family
An Australian Aboriginal cave painting
Isolating Mechanisms
• These are barriers lead to
reproductive isolation
• Prevents reproduction…further
isolates genes
A. Behavioral isolation
B. Temporal Isolation
C. Geographic isolation
A. Behavioral Isolation
• Different courtship patterns, hibernation
or estivation patterns, living habits, etc.
• May totally be different where two
populations are no longer able to
reproduce
B. Temporal Isolation
• Different mating times for species
• Different pollination times for plants
Wood frogs mate in late
March, Leopard frogs mate in
mid April
Since both are of the genus
Rana, they can interbreed but
do not
Wood & Leopard Frogs
C. Geographical Isolation
• Physical barriers separated populations.
• Over time, they develop two totally
different gene pools
The story of the fruit flies
1.
2.
3.
4.
A bunch of flies were minding their own business eating a banana
A hurricane washed the banana & flies onto an island
Since conditions & food are different on the island, the flies evolve
separate from their mainland relatives
When some of the flies mix with the mainland relatives, they can no
longer produce viable offspring when they mate.
Speciation has occurred!!
Extinction
• 99% of all species that ever inhabited
this earth have gone extinct!!
• Mass extinctions
– Lead open habitats/niches to be
filled by surviving populations.
– Leads to evolution of new species
– Actually considered GOOD for
evolution
Coevolution
• Two totally unrelated species evolve in
response to changes in each other
over time.
• Bees don’t see red, but do see yellow, blue,
and UV. Thus, bee-pollinated flowers are
mostly yellow or blue with UV nectar guides
(landing patterns) to guide the bee
• Birds, like hummingbirds have good eyes
which can see red
Evolutionary Rates
•
Gradualism – evolution is a
constant process and
occurs at a steady rate
Punctuated equilibriumPeriods of equilibrium
followed by rapid periods
of change.
•
–
–
Change occurs with
environmental pressures
Species arise abruptly then
have long periods of little
change