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Evolution
Chapter 4
How Did We Become Such a
Powerful Species So Quickly?
3 Main Adaptive Traits

Opposable Thumbs

Ability to Walk Upright

Intelligence (Complex
Brains)
Fig. 4-1, p. 63
How Do We Know Which
Organisms Lived in the Past?

Fossil record

Radiometric dating

Ice cores

DNA studies
Fig. 4-2, p. 65
Origins of Life
Considerable evidence suggests
that life developed in 2 phases
over the past 4.6-4.7 billion years.

Chemical evolution (1 billion yrs)

Biological evolution (3.7 billion years)
Question #1:
What is biological evolution by
natural selection, and how has it led
to the current diversity of organisms
on earth?
Include the importance of variation
within the gene pool and mutation on
microevolution and how this relates
to adaptations.
Biological Evolution

Biological Evolution

Theory of Evolution
• Microevolution

Mutations
Natural Selection
1)
2)
3)
Variation exists for a trait
Traits is heritable – can be passed on
to offspring
Individuals w/ trait are better able to
survive, reproduce & spread the trait
In a polluted environment…
Adaptations
Natural selection works on individuals,
Evolution occurs in populations!

Adaptations

Coevolution
How microevolution occurs…

Genes mutate,

Individuals are selected,

and Populations evolve!
Question #2:
How does the formation of
new species (speciation) and
extinction of species affect
biodiversity?
Explain the mechanism of
speciation and how this
increases biodiversity.
Macroevolution

Speciation
• Increases biodiversity

Extinction
• Decreases biodiversity

Speciation – Extinction = Current Biodiversity
Mechanism of Speciation

Geographic Isolation
• 2 groups from same species become physically
separated for long time period

Reproductive Isolation
• Mutation & natural selection act on separated
populations
• Each group adapts to different environmental
conditions
• Over time, leads to formation of 2 new species
Geographic Isolation can Lead to
Speciation
Arctic Fox
Northern
population
Early fox
population
Spreads northward
and southward
and separates
Adapted to cold
through heavier
fur, short ears,
short legs, short
nose. White fur
matches snow
for camouflage.
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Gray Fox
Southern
population
Adapted to heat
through
lightweight fur
and long ears,
legs, and nose,
which give off
more heat.
Fig. 4-7, p. 71
Question #3:
Define ecological niche.
Distinguish between
fundamental niche and
realized niche.
List the factors that determine
the realized niche.
Ecological Niches and
Adaptation

Ecological Niche (Occupation)

Habitats (Address)
Fundamental
Niche
Realized
Niche
Question #4:
Distinguish between a
specialist and a generalist.
Evaluate the conditions that
favor these two approaches.
Generalist Species

Broad Niches
• can live in many places
• can eat a variety of foods
• can tolerate a wide range of environmental
conditions
Cockroaches: Nature’s Ultimate
Survivors
Fig. 4-A, p. 69
Specialist Species

Occupy narrow niches
(may only have 1 possible habitat)
• use few food types
• can only tolerate a narrow range of
environmental conditions
• more prone to extinction when
environment changes
• reduces competition &
allows for sharing of
limited resources
Specialized Feeding Niches for Birds
Black skimmer
seizes small fish
at water surface
Scaup and other
diving ducks feed on
mollusks, crustaceans,
and aquatic vegetation
Flamingo
feeds on
minute
organisms
in mud
Herring gull is a
tireless scavenger
Brown pelican dives for fish,
which it locates from the air
Avocet sweeps bill through
mud and surface water in
search of small crustaceans,
insects, and seeds
Louisiana heron wades into
water to seize small fish
Dowitcher probes deeply
into mud in search of
snails, marine worms,
and small crustaceans
Oystercatcher feeds on
clams, mussels, and
other shellfish into which
it pries its narrow beak
Ruddy turnstone
searches
under shells and
pebbles for small
invertebrates
Knot (a sandpiper) picks up
worms and small crustaceans
left by receding tide
Piping plover feeds
on insects and tiny
crustaceans on
sandy beaches
If resources are limited, natural selection
favors specialized species.
Evolutionary Divergence of
Honeycreepers
Fruit and seed eaters
Insect and nectar eaters
Greater Koa-finch
Kuai Akialaoa
Amakihi
Kona Grosbeak
Crested Honeycreeper
Akiapolaau
Maui Parrotbill
Unknown finch ancestor
Apapane
Fig. 4-6, p. 70
Broad and Narrow Niches

Generalist species
• Better able to survive rapidly changing
environmental conditions

Specialist species
• Benefit under constant environmental
conditions (reduces competition)
Number of individuals
Niches of Specialist and
Generalist Species
Specialist species
with a narrow niche
Niche
separation
Generalist species
with a broad niche
Niche
breadth
Region of
niche overlap
Resource use
Fig. 4-4, p. 68
Limits on Adaptation

A population’s ability to adapt is limited
by it’s gene pool & the speed with which
it can reproduce

Natural selection can only work on
currently existing traits (beneficial
adaptations are rare)

Rapid reproducers are able to adapt
much more quickly to changes in
environment
Question #5:
How is “survival of the fittest”
different from the idea of
“progress to perfection”?
Evolution Misconceptions


Survival of the “fittest” refers to
reproductive success – not strength!
Evolution doesn’t lead to genetic
perfection, just works to select for best
traits for the current environmental
conditions.
• Organism best suited to environment,
survives & reproduces. Helpful traits are
then passed on!
Question #6:
How can genetic engineering
affect our ecosystems?
Future of Evolution

Genetic Engineering (gene splicing)

Genetically Modified Organisms
(GMOs)

Ethical concerns
Ecological Lesson

Whenever we intervene in nature, we
must pause & ask “What happens next?”

Evaluate possible unintended
consequences of biotechnology.