chapter 13 : how populations evolve?ppt

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
From PowerPoint® Lectures for Biology: Concepts & Connections
CHAPTER 13
How Populations Evolve
Modules 13.1 – 13.3

• All organisms have evolutionary adaptations
– Inherited characteristics that enhance their
ability to survive and reproduce
• The blue-footed booby of the
Galápagos Islands has features
that help it succeed in its
environment
– Large, webbed feet help
propel the bird through
water at high speeds
Clown, Fool, or Simply Well Adapted?

• Aristotle and the culture of the 1800’s believed
that species are fixed
• Fossils suggested that life forms change
– This idea was embraced by Lamarck in the early
1800s
13.1 A sea voyage helped Darwin frame his theory
of evolution
EVIDENCE OF EVOLUTION

• While on the voyage of the HMS Beagle in the
1830s, Charles Darwin observed
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as blue-footed boobies and giant tortoises
Figure 13.1A

• The voyage of the Beagle
Figure 13.1B
North
America
Great
Britain Europe
Africa
Equator
Australia
Tasmania
New
Zealand
Cape of
Good Hope
South
America
Cape Horn
Tierra del Fuego
Galápagos
Islands
Pacific
Ocean
Atlantic
Ocean

• Darwin became convinced that the Earth was
old and continually changing
– He concluded that living things also change, or
evolve over generations
– He also stated that living species descended
from earlier life-forms: descent with
modification

• Fossils and the fossil record
strongly support the theory of
evolution
– Hominid skull
13.2 The study of fossils provides strong evidence
for evolution
Figure 13.2A, B
– Petrified trees

– Scorpion in amber
– “Ice Man”
Figure 13.2E, F

• The fossil record shows that
organisms have appeared in a
historical sequence
• Many fossils link
early extinct species
with species living
today
– These fossilized
hind leg bones link
living whales with
their land-dwelling
ancestors
Figure 13.2G, H

• Other evidence for evolution comes from
– Biogeography
– Comparative
anatomy
– Comparative
embryology
13.3 A mass of evidence validates the evolutionary
view of life
Figure 13.3A
Human Cat Whale Bat

– Molecular biology
Figure 13.3B
Human Rhesus monkey Mouse Chicken Frog Lamprey
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
80 MYA
275 MYA
330 MYA
450 MYA

• Darwin observed that (Natural Selection)
– organisms produce more offspring than the
environment can support
– organisms vary in many characteristics
– these variations can be inherited
– organisms that are better adapted leave more
offspring
13.4 Darwin proposed natural selection as the
mechanism of evolution
DARWIN’S THEORY AND THE MODERN
SYNTHESIS

Darwin’s Four Criteria for Natural
Selection to Occur
• Overproduction of offspring leads to more
offspring than environment can support
• Variation in those offspring
• Variations are inherited
• Offspring that are better adapted to
environment leave subsequently more
offspring

• Darwin concluded that individuals best suited
for a particular environment are more likely to
survive and reproduce than those less well
adapted
• Darwin saw natural selection as the basic
mechanism of evolution
– As a result, the proportion of individuals with
favorable characteristics increases
– Populations gradually change in response to the
environment

Darwin also saw that when
humans choose organisms
with specific
characteristics as breeding
stock, they are performing
the role of the environment
– This is called artificial
selection
Figure 13.4A
Adopt me!!

• Evolutionary adaptations have been observed
in populations of birds, insects, and many other
organisms
– Example: camouflage adaptations of mantids
that live in different environments
13.5 Connection: Scientists can observe natural
selection in action
Figure 13.5A

• The evolution of insecticide resistance is an
example of natural selection in action
Figure 13.5B
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Insecticide
application

• A species is a group of
populations whose individuals
can interbreed and produce
fertile offspring
• A population is a group of
interbreeding individuals
living in same place and same
time.
– Populations evolve, not
individuals!!!
13.6 Populations are the units of evolution
Figure 13.6

• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool
13.7 Microevolution is change in a population’s
gene pool over time

• Hardy-Weinberg equilibrium
states that the shuffling of
genes during sexual
reproduction does not alter
the proportions of different
alleles in a gene pool
– To test this, let’s look at an
imaginary, nonevolving
population of blue-footed
boobies
13.8 The gene pool of a nonevolving population
remains constant over the generations
Figure 13.8A
Webbing No webbing

• We can follow alleles in a population to observe
if Hardy-Weinberg equilibrium exists
Figure 13.8B
Phenotypes
Genotypes
Number of animals
(total = 500)
WW
320
Ww
160
ww
20
Genotype frequencies 320/500 = 0.64 160/500 = 0.32 20/500 = 0.04
640 W 160 W + 160 w 40 w
800/1,000 = 0.8 W 200/1,000 = 0.2 w
Number of alleles
in gene pool
(total = 1,000)
Allele frequencies

Figure 13.8C
Recombination
of alleles from
parent generation
Next generation:
Genotype frequencies
Allele frequencies
SPERM EGGS
0.64 WW 0.32 Ww 0.04 ww
0.8 W 0.2 w
WW
p2 = 0.64
WW
qp = 0.16
Ww
pq = 0.16
ww
q2 = 0.04

• The population is very large
• The population is isolated
• Mutations do not alter the gene pool
• Mating is random
• All individuals are equal in reproductive success
13.10 Five conditions are required for Hardy-
Weinberg equilibrium

What is Hardy-Weinberg Equilibrium????
• It just means that the gene pool is in
equilibrium.
• Allele frequency is not changing
• POPULATION IS NOT EVOLVING!!!

• Genetic drift is
a change in a
gene pool due
to chance
– Genetic drift
can cause the
bottleneck
effect
13.11 There are several potential causes of
microevolution
Figure 13.11A
Original
population
Bottlenecking
event
Surviving
population

– or the founder effect
Figure 13.11B, C

• Gene flow can change a gene pool due to the
movement of genes into or out of a population
• Mutation changes alleles
• Natural selection leads to differential
reproductive success

Five Fingers of Evolution
(Causes of Microevolution)
• Small population size
• Non-random mating
• Mutations
• Gene flow (migration)
• Natural selection

• Natural selection results in the accumulation of
traits that adapt a population to its environment
– If the environment should change, natural
selection would favor traits adapted to the new
conditions
13.12 Adaptive change results when natural
selection upsets genetic equilibrium

• Phenotypic variation may be environmental or
genetic in origin
– But only genetic changes result in evolutionary
adaptation
13.13 Variation is extensive in most populations
VARIATION AND NATURAL SELECTION

• Many populations exhibit polymorphism and
geographic variation
Figure 13.13

13.14 Connection: Mutation and sexual
recombination generate variation
Figure 13.14
Parents A1 A1 A2 A3
A1 A2 A3
A1 A2 A1 A3
and
MEIOSIS
Gametes
FERTILIZATION
Offspring,
with new
combinations
of alleles

• Natural selection tends to reduce variability in
populations
– The diploid condition preserves variation by
“hiding” recessive alleles
– Balanced polymorphism may result from the
heterozygote advantage
13.15 Overview: How natural selection affects
variation

• Some variations may be neutral, providing no
apparent advantage or disadvantage
– Example: human fingerprints
13.16 Not all genetic variation may be subject to
natural selection
Figure 13.16

• Low genetic variability may reduce the capacity
of endangered species to survive as humans
continue to alter the environment
– Studies have shown that cheetah populations
exhibit extreme genetic uniformity
– Thus they may have a
reduced capacity to
adapt to environmental
challenges
13.17 Connection: Endangered species often have
reduced variation
Figure 13.17

• An individual’s Darwinian fitness is the
contribution it makes to the gene pool of the
next generation relative to the contribution
made by other individuals
• Production of fertile offspring is the only score
that counts in natural selection
13.18 The perpetuation of genes defines
evolutionary fitness

13.19 There are three general outcomes of natural
selection
Figure 13.19
Frequency
of
individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection Directional selection Diversifying selection

• Sexual selection leads to the evolution of
secondary sexual characteristics
– These may give individuals an advantage in
mating
13.20 Sexual selection may produce sexual
dimorphism
Figure 13.20A, B

• This is due to:
– historical constraints
– adaptive compromises
– chance events
– availability of variations
13.21 Natural selection cannot fashion perfect
organisms

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