Transcript Mechanisms for Evolution

Mechanisms for
Evolution
Lamark vs. Darwin
Differing Viewpoints…
 Charles Darwin
 Characteristics among members of a
species vary.
 Only individuals with the characteristics best
suited to the environment will survive to
reproduce.
 Over time characteristics will increase in the
population.
 (Now called Natural Selection)
Differing Viewpoints
 Jean
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Lamark
Evolution occurs through the use and
disuse of physical features.
Over an organisms lifetime features will
increases by use or decrease by disuse.
These traits are than passed down to their
offspring.
Lamark vs. Darwin
Natural Selection
 Process
by which populations change in
response to their environments.
 Key components of natural selection:
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Genetic Variation
Competition and Struggle for existence
Survival of the fittest (Variation is Selected)
Increased frequency of best traits (Variation is
inherited)
Requirement #1: Genetic Variation

Exists within a population
through
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Meiosis – genetic variation
is increased during crossing
over
Mutations- spontaneous
changes in DNA
Genetic Recombination –
occurs during sexual
reproduction and provides
endless source of new
variations
Requirement #2:
Struggle for Existence
 Every
organism must
constantly fight for
limited resources
(food, water, mates)
and escape from
predators in order to
survive long enough
to reproduce.
Requirement # 2
Reproduction Leads to Competition

When conditions are
favorable organisms
tend to produce many
offspring.
 When resources
become scarce:
competition occurs.
Requirement #3
Survival of the Fittest

Individuals best
suited/adapted to their
environments have the
best chances for
survival

Those individuals
Reproduce more often
and pass those good
traits that allowed
survival on to their
offspring.
End Result:
Increased frequency of best traits

Over time, good
traits appear
more in a
population
because more
individuals
survive and
reproduce.
Examples of Natural Selection

Sickle Cell Anemia
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Hereditary disease that
affects hemoglobin
• Protein in our blood that
carries oxygen
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
1/500 have Sickle Cell
Anemia in US
1/100 have Sickle Cell
Anemia in Central Africa
 Malaria
is a warm climate
disease caused by a parasite
that is transmitted by
mosquitoes.
 Causes death if not treated.
 People with sickle cell anemia
are more resistant to malaria
•AA = normal blood (no resistance)
•Aa = both normal and sickle
shaped blood (resistance)
•aa = all sickle shaped blood
(resistance)
Types of Natural Selection
1)
Balancing Selection (Stabilizing Selection)
* When selective pressures select against
the two extremes of a trait.
AA
Aa
aa
Another Example
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The Peppered Moth
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White or black and
sits on the bark of
trees
Pray to birds

Industrial revolution

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Increased pollution
Killed lichens on trees
• Trees covered in lichens
appear more white while trees
without lichens appear dark
What Happened?

Lots of Pollution:

No pollution:
Try It….
 http://www3.district125.k12.il.us/faculty/nfi
scher/Moth/default.htm
2) Directional Selection
* When selective pressures are against
one extreme.
White Moths
Black Moths
Another Example

Imagine rabbits with fur that can either be black,
grey, or white (due to incomplete dominance)
 The environment consists of black rock
outcroppings, and white snowy tundra.
 Animals that are born with the heterozygous
grey coats are going to be spotted easily by their
predators. Animals with black or white fur are
likely to survive and reproduce more offspring
than gray rabbits.
3) Disruptive Selection
* When selection acts against individuals
in the middle of the trait.
White rabbits
Grey rabbits
Black Rabbits
Adaptations
 An
adaptation is an physical structure,
physiological process or behavioral trait of
an organism that has evolved over a
period of time by the process of natural
selection.
 Adaptations increase the reproductive
success of the organism.
Adaptations
 Organisms
that are adapted to their
environment are able to:
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obtain air, water, food and nutrients
cope with physical conditions such as
temperature, light and heat
defend themselves from their natural enemies
reproduce
respond to changes around them
Types of Adaptations
1) Morphological – structures are adapted
to specific needs and environments.
Floating Leaves
Turtles shell
2) Behavioral Adaptations – based on
behavior
Bird Migration
Living in herds/schools
3) Physiological Adaptations – Adaptations
on a molecular level
* Things inside the body vs. outside
Bioluminescent –deep sea
Poisons- Dart Frog
Speciation

If a species changes enough that it
can no longer interbreed with the
original species a new species can
form.
Types of Reproductive Isolation:
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Reproductive Isolation-If a population becomes isolated
and can’t interbreed, changes can accumulate and a new
species can form
 Three
Types…
1. Geographical Isolation
2. Temporal Isolation
3. Behavioral Isolation
1) Geographical Isolation
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Separation by land forms or physical
features
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Examples: Rivers, mountains, islands
Darwin’s Finches
•Galápagos Islands – had different
environments
•14 species of finches arose by
speciation from a single South
American species.
•Populations of finches can no
longer interbreed.
Finches Beaks
2) Temporal Isolation
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Separated by time of day or year reproduction occurs
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Examples: gamete exchange during different
seasons
Frogs:
Rana aurora - breeds January - March
Rana boylei - breeds late March - May
Fruit Flys:
Drosophila persimilis - breeds in early morning
Drosophila pseudoobscura - breeds in the afternoon
3) Behavioral Isolation
 Separated
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by behavior
Examples: Bird/frog calls, different courtship
behaviors, lighting patterns of lightning bugs.
Patterns in Evolution

Convergence – Unrelated organisms develop similar
traits. Different geographical areas sometimes exhibit
groups of plants and animals of strikingly similar
appearance, even though the organisms may be only
distantly related.
Patterns in Evolution
 Divergence
– two related species become
increasingly different. Organisms evolve to fill
diverse ecological niches. (In the broadest
sense, all current species are the result of
divergent evolution.)