Transcript Chapter 22.

Darwin’s Principles &
Evidence of Evolution
by Natural Selection
AP Biology
2007-2008
Dodo bird
Essence of Darwin’s ideas
(1) Variation exists in natural populations
(2) Many more offspring are born each season
than can possibly survive to maturity
(3) As a result, there is a struggle for existence
- competition
(4) Characteristics beneficial in the struggle
for existence will tend to become more
common in the population, changing the
average characteristics of the population
- adaptations
(5) Over long periods of time, and given a steady input of
new variation into a population, these processes lead to
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the emergence of new species
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
Fossil record
 Layers of sedimentary rock contain fossils
new layers cover older ones, creating a
record over time
 fossils within layers show that a
succession of organisms have populated
Earth throughout a long period of time

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Fossil record
 A record showing us that today’s organisms
descended from ancestral species
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Anatomical record
 Homologous structures

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similarities in characteristics resulting
from common ancestry
Homologous structures
 Similar structure
 Similar development
 Different functions
 Evidence of close
evolutionary relationship

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recent common ancestor
Vestigial organs
 Modern animals may have structures that
serve little or no function


remnants of structures that were functional in
ancestral species
deleterious mutations accumulate in genes for
non-critical structures without reducing fitness
 snakes & whales — remains of pelvis & leg bones of
walking ancestors
 eyes on blind cave fish
 human tail bone
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This is not
LaMarck’s loss
from “disuse”!
Vestigial organs
 Hind leg bones on whale fossils
Why would whales
have pelvis & leg bones
if they were always
sea creatures?
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Comparative embryology
 Similar embryological development in
closely related species

all vertebrate embryos have similar
structures at different stages of
development
 gill pouch in fish, frog, snake, birds, human, etc.
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Molecular record
 Comparing DNA & protein structure

universal genetic code!
 DNA & RNA

compare common genes
Human/kangaroo
Closely related species have
sequences that are more similar
than distantly related species
 DNA & proteins are a molecular
record of evolutionary relationships
Nucleotide substitutions
100
75
Rabbit/
rodent
50 Horse/
donkey
Llama/
cow
Human/rodent
Horse/cow
Sheep/
goat
25
Pig/
cow
Goat/cow
0
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Dog/
cow
Human/
cow
0
25
50
75
100
Millions of years ago
125
Artificial selection
 Artificial breeding can use variations in
populations to create vastly different
“breeds” & “varieties”
“descendants” of wild mustard
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“descendants” of the wolf
Natural selection in action
 Insecticide &
drug resistance
insecticide didn’t
kill all individuals
 resistant survivors
reproduce
 resistance is inherited
 insecticide becomes
less & less effective

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Homework
 Explain 4 pieces of evidence
supporting Darwin’s Theory of
Evolution. For each one, give a specific
example and make sure you explain
WHY it serves as evidence for
evolution.
(could be in theme of paleontology,
biogeography, embryology,
comparative anatomy, molecular
biology, etc.)
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