Chapter 15
Darwin and Evolution
Darwin: a
reluctant
rebel
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2006-2007
Evolution explains the Diversity and Unity of life
1. Diversity – the abundance of different
forms of living things on Earth
2. Unity – the biochemical, cellular, genetic,
and physiological characteristics/processes
common to all living things
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What is Evolution?
 The change in a species over time (i.e. the
gene pool changes due to adaptations)
1. The Process: Descent thru Modification
 new life comes into existence over time
 all species come from common ancestry
 all species comes from existing species
via modification
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History of Evolutionary Thought
 Carolus Linnaeus (17071778)
Taxonomist
 Binomial Nomenclature
 Agreed with the “fixity of
species” theory
 However, he performed
hybridization experiments
which made him think a
species might change
with time

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LaMarck
 Organisms adapted to
their environments by
acquiring traits

change in their life time
 Disuse
organisms lost parts because they did not use them
— like the missing eyes & digestive system of the
tapeworm
 Perfection with Use & Need
the constant use of an organ leads that organ to
increase in size — like the muscles of a blacksmith
or the large ears of a night-flying bat

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transmit acquired characteristics to next
generation
History of Evolutionary Thought
 Alfred Wallace (1823 -1913)
 British naturalist
 came up with the same theory
as Darwin independently

Natural Selection (Survival of the
Fittest)
 Darwin’s and Wallace’s ideas

were published at the same
time
But Wallace did not have as
much evidence as Darwin
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Charles Darwin
 1809-1882
 British naturalist
 Proposed the idea of
evolution by natural
selection:

Organisms that are best
fit for the environment,
survive and reproduce
(“survival of the fittest”)
 Collected clear
evidence to support his
ideas
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LaMarckian vs. Darwinian view
 LaMarck

in reaching higher
vegetation giraffes
stretch their necks &
transmits the acquired
longer neck to offspring

 Darwin

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giraffes born with longer
necks survive better &
leave more offspring who
inherit their long necks
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

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500 miles off coast of Ecuador
Galapagos
Recent volcanic origin most
of animal species on the
Galápagos live nowhere else
in world, but they resemble
species living on South
American mainland.
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500 miles west of mainland
Darwin found… birds
Collected many
different birds on the
Galapagos Islands.
Finch?
Thought he found
very different kinds…
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Sparrow?
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Photo - JPEG decompressor
are needed to see this picture.
Woodpecker?
Warbler?
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!
Finch?
Large
Ground
Finch?
Finch
Sparrow?
Small
Ground
Sparrow?
Finch
How did
one species
of finches become
so many different
species now?
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Woodpecker?
Warbler
Finch
Woodpecker?
Warbler?
Veg.Warbler?
Tree Finch
Tree Thinking
Descendant
species
Ancestral
species
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Large-seed
Large Ground
eater?
Finch
Warbler?
Warbler
Finch
Small-seed
Small Ground
eater?
Finch
Leaf-browser?
Veg. Tree Finch
Correlation of species to food source
Seed
eaters
Flower
eaters
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Adaptive
Insect
eaters
Rapid speciation:
new species filling new niches,
because they inherited
successful adaptations.
Voyage: 1831-1836
November 24, 1859, Darwin published
“On the Origin of Species by Means of Natural Selection”
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Natural Selection: 4 steps
1. Natural Variation exists in nature
2. Competition - Organisms struggle for
3.
4.
survival: more organisms are produced than
the environment can support
Survival of the fittest: Only the best adapted
survives. Adaptations are important
Organisms change over time in response to
the environment: organisms change but they
have a common descent – they have common
ancestors
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Adaptations:
inherited characteristics that
allow individuals to “do
better” in their environment.
Adaptations increase their
chance of survival and
reproduction
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Types of Natural Selection
a. Directional – a shift in the freq.
of a trait in a particular
direction
 common in changing
env’ts
Ex. Horseracing:
pick horses that can
run fastest
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b. Stabilizing – selects for
avg. pheno. and against
extreme pheno.
 common in stable,
unchanging env’t
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c. Disruptive – selects for
extreme pheno. and
against avg. pheno. b/c
subject to predation
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Artificial selection
This is not just a
process of the
past…
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It is all
around
us today
Selective breeding
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Natural Selection
vs. Artificial Selection
 Artificial Selection: nature provides
variation, and humans select
variations that we find useful
(domestic animals and crops)
 Natural Selection: the environment is
the selective force. Only those
organisms that are well adapted will
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survive in the wild.
Sexual Selection
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