Download Mechanisms of Evolution

• TEK: Analyze and evaluate how natural selection
produces change in populations, not
individuals.[7C]
LEARNING TARGET:
By the end of class today…
I can analyze and evaluate how
natural selection produces change
in populations, not individuals…
Natural
Selection
Mutations
Recombination
Gene Flow
Genetic Drift
What does this mean?
Artificial
Selection
Non-Random
Mating
Isolation
Evolution
• Changes in a population over time.
• Mechanisms of evolution
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Mutations
Gene flow
Genetic drift
Natural Selection (survival of the “fittest”)
Artificial Selection
Recombination
Non-Random Mating
Isolation
Mechanism of Evolution:
Mutations
Original Population
Mechanism of Evolution:
Mutations
After Mutation
Mechanism of Evolution:
Mutations
Many Generations
Later
Gene Flow
• Genes move with individuals when they move
(emigrate or immigrate) into and out of a
population…and it changes the gene pool
Genetic Drift
• Genetic Drift – the random fluctuation due to
chance occurrences alone
• It is more significant in smaller populations
• It increases the chance of any given allele
becoming more or less prevalent when the
number of individuals is small
Non-Random Mating
Original Population
Blue = BB or Bb
Red = bb
x
Non-Random Mating
Many Generations
Later
Recombination & Genetic Shuffling
As we learned in the genetics unit, recombination leads
to genetic material being shuffled.
This shuffling, along with sexual reproduction, leads to
variation within populations. This variation leads to
selection, which ultimately leads to evolution.
What is the difference between artificial and
natural selection?
• Breeding organisms with specific traits in
order to produce offspring with ideal traits is
called artificial selection.
(Intentional breeding for certain traits)
A Goldendoodle
(Golden retriever/ Poodle)
Natural Selection
• Natural selection is the idea that organisms with
favorable/beneficial traits survive, reproduce, and pass
those traits to the next generation.
ENVIRONMENTALLY CONTROLLED
• Organisms without these variations/traits are less
likely to survive and reproduce.
Darwin and Natural Selection
• Charles Darwin (1809- 1882)
He was an English scientist and it took him years
to develop his theory of natural selection.
• He began in 1831 at age 22 when he took a job as a naturalist
on the English ship HMS Beagle, which sailed around the world
on a five-year scientific journey.
Darwin and Natural Selection
• One of the things Darwin
observed is that in nature,
the traits of individuals vary
in populations.
• Then these variations are
passed to offspring.
• Darwin hypothesized that there was a force in nature
that picked traits which are better for survival in a
species.
Darwin and Natural Selection
• He also observed that individuals struggle to compete
in changing environmental conditions.
• What do individuals compete for?
RESOURCES
• Only some individuals survive the competition and live
to produce offspring.
ADAPTATIONS
• Recall that an adaptation is any variation that aids an
organism’s chances of survival in its environment.
• Examples are:
Thorns on plants
Special colorings for an organism
Enhanced night vision
ADAPTATIONS
• Some other structural adaptations are subtle.
• Mimicry is a structural adaptation that enables one
species to resemble another species.
• In one form of mimicry, a harmless species has
adaptations that result in a physical resemblance to a
harmful species.
ADAPTATIONS
• Another subtle adaptation is camouflage, an
adaptation that enables species to blend with their
surroundings.
• Because well-camouflaged organisms are
not easily found by predators, they survive to
reproduce.
Darwin’s 5 points
1. Population has variations.
2. Some variations are favorable.
3. More offspring are produced than
survive
4. Those that survive have favorable
traits.
5. A population will change over time.
NATURAL SELECTION
• There are three different types of natural selection:
stabilizing, directional, and disruptive.
• Stabilizing selection is a natural selection that
favors average individuals in a population.
Evolution will
not occur
Middle sized Siberian Huskies are selected for
NATURAL SELECTION
• Directional selection occurs when natural selection
favors one of the extreme variations of a trait.
• This type of selection can lead to rapid evolution of
a population.
NATURAL SELECTION
• In disruptive selection, individuals with either
extreme of a trait’s variation are selected for.
• This results in eventually having no intermediate
form of a trait, and leading to two separate species.
Natural Selection on Polygenic Traits
• Shifts to
middle range
• Shifts to
2 extremes
• Shifts to
1 extreme
SPECIATION
• The evolution of new
species, a process called
speciation.
• This occurs when members of
similar populations change so
much from each other that they
no longer interbreed to produce
fertile offspring.
SPECIATION
• In nature, physical barriers
can break large populations
into smaller ones.
• Geographic isolation occurs
whenever a physical barrier
divides a population and over
time they change and become two
different species.
•Reproductive isolation…
SPECIATION
without a physical barrier
• Some speciation occurs while the
organisms still exist in the same area…
•Reproductive Isolation
•Behavioral, Temporal, Mechanical
Speciation
Northern
population
Early fox
population
Spreads
northward
and
southward
and
separates
Arctic Fox
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Southern
population
Gray Fox
Adapted to cold
through heavier
fur, short ears,
short legs, short
nose. White fur
matches snow
for camouflage.
Adapted to heat
through lightweight
fur and long ears,
legs, and nose, which
give off more heat.
Types of Change
• Divergent evolution is when species that are similar
and closely related become increasingly different from
each other. THEY DIVERGE
This is also called Adaptive Radiation….because it has to do with ADAPTING to
different environments and RADIATING out into different species.
Types of Change
• When distantly-related organisms evolve to become
more similar, it is called convergent evolution.
• Convergent evolution occurs when unrelated
species occupy similar environments in different
parts of the world.
Also: Co-Evolution & Parallel Evolution
Rate of Speciation
• Current debate:
Does speciation happen gradually or
rapidly? Or both?
– Gradualism
– Punctuated equilibrium
Gradualism
 Gradual change
over long spans of
time
assume that big
changes occur as
the accumulation of
many small ones
develop over time.
Punctuated Equilibrium
• Rate of speciation is
not constant
– rapid bursts of change
– long periods of no
change
– species undergo rapid
change when they 1st
bud from parent
population
Time