Transcript Darwin & Evolution by Natural Selection

Chapter 15
Evolution:
Evidence and
Theory
Cactus
eater
Insect eaters
Seed eaters
Bud eater
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2006-2007
Charles Darwin
 Proposed a way how
evolution works
How did creatures
change over time?
 by natural selection

 Collected a lot of
evidence to support
his ideas
1809-1882
 British naturalist

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Voyage of the HMS Beagle
 Invited to travel around the world
1831-1836 (22 years old!)
 makes many observations of nature

 main mission of the Beagle was to chart
South American coastline
Robert Fitzroy
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Voyage of the HMS Beagle
 Stopped in Galapagos Islands

500 miles off coast of Ecuador
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Galapagos
Recently formed volcanic
islands. Most of animals on
the Galápagos live nowhere
else in world, but they look
like species living on South
American mainland.
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800 km west of Ecuador
Darwin found…many unique species
Many of Darwin’s observations made him wonder… Why?
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Why were these creatures found only on the Galapagos Islands?
Darwin found…clues in the fossils
Darwin found:
Evidence that creatures
have changed over time
present day Armadillos
Darwin asked:
ancient Armadillo
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Why should extinct
armadillos & modern
armadillos be found on
same continent?
Darwin found… more fossils
Darwin found:
Evidence that creatures
have changed over time
(extinct) Giant ground sloth
present day Sloth
Darwin asked:
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Why should
extinct sloths &
modern sloths be
found on the same
continent?
Darwin found:
Different shells on tortoises on different islands
Darwin asked:
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Is there a relationship
between the
environment & what an
animal
looks like?
Darwin found… birds
Darwin found:
Many different birds on the Galapagos Islands.
He thought he found very different kinds…
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But Darwin found… a lot of
finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
species of finch on the
mainland!
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Finch?
Sparrow?
Darwin asked:
If the Galapagos
finches came from the
mainland, why are they
so different now?
Warbler?
Woodpecker?
The finches cinched it!
Darwin found:
The differences
between species of
finches were
associated with the
different food they
ate.
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different beaks are
inherited variations
serve as adaptations
that help birds
compete for food
these birds survive &
reproduce
pass on the genes for
those more fit beaks
over time nature
selected for different
species with different
beaks
Relationship between species (beaks) & food
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Darwin’s finches
 Darwin’s conclusions

variations in beaks
 differences in beaks in the original flock
 adaptations to foods available on islands

natural selection for most fit
 over many generations, the finches were
selected for specific beaks & behaviors

offspring inherit successful traits
 accumulation of winning traits:
both beaks & behaviors
separate into different species

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From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small
insectivorous
tree finch
Large
insectivorous
tree finch
Small
ground
finch
Cactus
eater
Insect eaters
Seed eaters
Vegetarian
tree finch
variation
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Bud eater
Medium
ground
finch
Large
ground
finch
natural selection for best
survival & reproduction
Earlier ideas on Evolution
 LaMarck

evolution by acquired
traits
 creatures developed
traits during their lifetime
 give those traits to their
offspring

example
 in reaching higher
leaves giraffes stretch
their necks & give the
acquired longer neck to
offspring

not accepted as valid
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Darwin’s view of Evolution
 Darwin
giraffes that already
have long necks
survive better
 leave more offspring
who inherit their long
necks
 variation
 selection &

survival
 reproduction &
inheritance of
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Evidence supporting evolution
 Fossil record

shows change over time
 Anatomical record

comparing body structures
 homology & vestigial structures
 embryology & development
 Molecular record

comparing protein & DNA
sequences
 Artificial selection
human caused evolution

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1. Fossil record
 Layers of rock contain fossils

new layers cover older ones
 creates a record over time

fossils show a series of organisms have
lived on Earth
 over a long period of time
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Fossils tell a story…
the Earth is old
Life is old
Life on Earth has changed
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Evolution of birds
Today’s organisms
descended from
ancestral species
Fossil of Archaeopteryx
 lived about 150 mya
 links reptiles & birds
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We found the fossil — no joke!
Land Mammal
?
?
?
Complete series
of transitional
fossils
Someone’s idea of a joke!
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ButBiology
the joke’s
on them!!
Ocean Mammal
?
Evolution from sea to land
 2006 fossil discovery of early tetrapod

4 limbs
 Missing link from sea to land animals?
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2. Anatomical record
Animals with different
structures on the surface
But when you look under
the skin…
It tells an evolutionary story
of common ancestors
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Compare the bones
 The same bones under the skin

limbs that perform different functions
are built from the same bones
How could these
very different animals
have the
same bones?
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Homologous structures
 Structures that come from the same origin
 homo- = same
 -logous = information
 Forelimbs of human, cats, whales, & bats

same structure
 on the inside
same development in embryo
 different functions

 on the outside

evidence of common ancestor
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But don’t be fooled by these…
 Analogous structures

look similar
 on the outside
same function
 different structure & development

How is a bird
like a bug?
 on the inside
different origin
 no evolutionary relationship

Solving a similar problem with a similar solution
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Analogous structures
 Dolphins: aquatic mammal
 Fish: aquatic vertebrate
both adapted to
life in the sea
 not closely related

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Convergent evolution
 3 groups with wings

Does this mean they have a
recent common ancestor?
They just
came up
with the
NO!
same answer!
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Flight evolved 3
separate times —
evolving similar
solutions to similar
“problems”
Convergent evolution led to mimicry
 Why do these pairs look so similar?
Monarch male
Viceroy male
poisonous
edible
Which is the moth
vs.
the
bee?
fly vs. the bee?
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fly
bee
moth
bee
Vestigial organs
 Hind leg bones on whale fossils
Why would whales
have pelvis & leg
bones if they were
always sea creatures?
Because they
used to
walk on land!
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Vestigial organs
 Structures on modern animals that have
no function
remains of structures that were functional
in ancestors
 evidence of change over time

 some snakes & whales have pelvis bones &
leg bones of walking ancestors
 eyes on blind
cave fish
 human tail bone
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Comparative embryology
 Development of embryo tells an
evolutionary story

similar structures during development
all vertebrate embryos have a “gill
pouch” at one stage of development
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3. Molecular record
 Comparing DNA & protein structure

everyone uses the same genetic code!
 DNA
Human
Macaque
Dog Bird
Frog
Lamprey
8
32 45
67
125
 compare common genes
 compare common proteins
number of amino acids different
from human hemoglobin
0 10 20 30 40 50 60 70 80 90 100 110 120
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Building “family” trees-Phylogeny
Closely related species are branches on the tree —
coming from a common ancestor
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4. Artificial selection
 How do we know natural selection can
change a population?
we can recreate a similar process
 “evolution by human selection”
“descendants” of wild mustard

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Selective Breeding
Humans create the
change over time
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“descendants”
of the wolf
Artificial Selection
…and the
examples
keep coming!
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Artificial Selection gone bad!
 Unexpected
consequences of
artificial selection
Pesticide resistance
Antibiotic resistance
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Insecticide resistance
 Spray the field, but…

insecticide didn’t
kill all individuals
 variation
resistant survivors
reproduce
 resistance is inherited
 insecticide becomes
less & less effective

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Any Questions??
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2006-2007