Transcript Natural selection

Evolution – genetic change over time
Oldest multicellular fossil
Oldest fossil
prokaryotic cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 13-1b
Great
Britain
Europe
Asia
North
America
PACIFIC
OCEAN
The
Galápagos
Islands
PACIFIC
OCEAN
Pinta
Marchena
Pinzón
Isabela
0
0
40 km
Equator
Daphne
Islands
Santa Santa
Cruz Fe
Florenza
40 miles
Africa
San
Cristobal
Española
PACIFIC
OCEAN
Equator
South
America
Genovesa
Santiago
Fernandina
ATLANTIC
OCEAN
Australia
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Tasmania
New
Zealand
Natural Selection
Darwin proposed natural selection as the mechanism of evolution
•Organisms vary in many characteristics that can be inherited
•Excessive numbers of organisms lead to a struggle for survival
•Organisms produce more offspring than the environment can
support
What is a Species?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 13-2c
Natural selection is supported by evidence from artificial selection
African wild dog
Coyote
Wolf
Thousands to
millions of years
of natural selection
Ancestral canine
Fox
Jackal
LE 13-4a
–Common embryonic structures in all vertebrates are evidence for common descent
Human
Cat
Whale
Bat
LE 13-4b
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo
LE 13-5b
Chromosome with gene
conferring resistance
to pesticide
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Pesticide application
Survivor
• Examples of evolutionary adaptation reveal
three key points about natural selection
– Natural selection is more of an editing
process than a creative mechanism
– Natural selection is contingent on time and
place
– Significant evolutionary change can occur in
a short time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Studying evolution at the population level
– Evolution: change in the prevalence of
certain heritable characteristics in a
population over a span of generations
– Gene pool: the total collection of genes in a
population at any one time
– Microevolution: a change in the relative
frequencies of alleles in a gene pool
– Species: a group of populations capable of
interbreeding and producing fertile offspring
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 13-9a
In addition to natural selection, other events can contribute to evoluti
Original
population
Bottlenecking
event
Surviving
population
LE 13-12a
A1
Parents
A2
A1
A3

Meiosis
A1
Gametes
A2
A3
LE 13-12b
A1
A2
A3
Gametes
Fertilization
Offspring,
with new
combinations
of alleles
A1
A1
A2
and
A3
CONNECTION
13.13 The evolution of
antibiotic resistance in
bacteria is a serious public
health concern
•
Natural selection has
led to the evolution of
antibiotic-resistant
bacteria
•
Overuse and misuse
of antibiotics has
contributed to the
proliferation of
antibiotic-resistant
strains
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Neutral traits
13.15 The perpetuation of genes defines
evolutionary fitness
• Evolutionary fitness is the relative contribution
an individual makes to the gene pool of the
next generation
• Survival of genes depends on production of
fertile offspring
• Selection indirectly adapts a population to its
environment by acting on phenotype
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 13-16
Original
population
Evolved
population
Frequency of individuals
Natural selection can alter variation in a population
Original
population
Phenotypes (fur color)
Stabilizing selection
Directional selection
Disruptive selection
13.18 Natural selection cannot fashion perfect
organisms
• There are at least four reasons why natural
selection cannot produce perfection
– Organisms are limited by historical
constraints
– Adaptations are often compromises
– Chance and natural selection interact
– Selection can only edit existing variations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings