Copyri
ght
© G
lenco
e/M
cGra
w-H
ill,
a d
ivis
ion o
f T
he
McG
raw
-Hil
l C
om
pan
ies,
Inc.
Mutations, Variation, and Natural Selection
Recall that mutations can lead to changes in traits. Therefore, mutations can produce differences among individuals. Slight differences in inherited traits among individuals in a population are called variations.
In 1976, scientists measured several traits in a population of medium ground finches on one of the Galápagos Islands. They discovered that the birds had variations in beak size. Most had smaller beaks, but all of the birds of this species preferred to eat small, soft seeds. The next year, it did not rain on the island. None of the plants reproduced, so no seeds formed. After all of the small, soft seeds had been eaten, many of the finches died. The few seeds left were fairly large and hard. The birds that survived were those that could crack and eat these larger seeds. These finches tended to be the birds with fairly large beaks.
In 1978, the scientists measured the beaks of the surviving birds’ offspring. They compared the average beak size of birds hatched in 1978 to that of birds hatched in 1976. In just two years, the average beak size of birds in the population had increased. How did this happen?
What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.
Before Statement After
5. A population that lacks variation among its individuals might not be able to adapt to a changing environment.
6. Extinction occurs when the last individual of a species dies.
Key Concepts • How does natural selection
occur?• What is an adaptation?• Why do traits change over
time?
Building Vocabulary As you read, underline the words and phrases that you do not understand. When you finish reading, discuss these words and phrases with another student or your teacher.
Make a vertical three-tab book and use it to organize notes on the different types of adaptations.
Structural
Functional
Behavioral
Heredity and How Traits ChangeAdaptation and Evolution
Reading Essentials Heredity and How Traits Change 411
C210_015_020_RE_L3_889406.indd 15C210_015_020_RE_L3_889406.indd 15 2/19/10 4:36:28 PM2/19/10 4:36:28 PM
Copyrig
ht ©
Glen
coe/M
cGraw
-Hill, a d
ivisio
n o
f The M
cGraw
-Hill C
om
pan
ies, Inc.
Natural SelectionThe process by which individuals with variations that help them
survive in their environment live longer, compete better, and reproduce more than those individuals without these variations is called natural selection. For the finches, there was variation among individual birds for the trait of beak size. Some of the birds had small beaks, and some of them had larger beaks. When a change in the environment—a drought—occurred, the birds with larger beaks were better able to survive than birds with smaller beaks. The surviving individuals then passed on the favorable trait to their offspring. Over the two-year span of natural selection and reproduction, the average beak size of the birds in the population increased. The birds with larger beaks were naturally selected by environmental conditions and survived. Another example of natural selection in plants is shown in the figure below.
Key Concept Check1. Explain How does natural selection occur?
Visual Check2. Analyze What happened when individual sunflowers competed for limited resources?
Natural Selection: Sunflowers
1 Variation Individuals in a population differ from
one another. In this population, some sunflowers are
taller than others.
2 Inheritance Traits are inherited from parents. Tall
sunflowers produce tall sunflowers. Short sunflowers
produce short sunflowers.
3 Competition Due to limited resources, not all
offspring will survive. Individuals with a trait that
better suits the environment are more likely to
survive and reproduce. In this environment, short
sunflowers are more successful.
4 Natural Selection Over time, the average height of
the sunflower population is short if the short sunflowers
continue to reproduce successfully.
412 Heredity and How Traits Change Reading Essentials
C210_015_020_RE_L3_889406.indd 16C210_015_020_RE_L3_889406.indd 16 2/19/10 4:36:31 PM2/19/10 4:36:31 PM
Copyri
ght
© G
lenco
e/M
cGra
w-H
ill,
a d
ivis
ion o
f T
he
McG
raw
-Hil
l C
om
pan
ies,
Inc.
AdaptationsThe traits of surviving individuals, such as larger beaks or
shorter sunflowers, become more common as the survivors reproduce and pass the genes for their traits to their offspring. An adaptation is an inherited trait that increases an organism’s chance of surviving and reproducing in a particular environment. Adaptations can be structural, functional, or behavioral.
Structural AdaptationsA flying squirrel has a flap of skin between its forelegs
and hind legs. This flap of skin enables the squirrel to glide distances of up to 45 m. The behavior possibly is used to escape from predators. This flap of skin is an example of a structural adaptation. Structural adaptations involve physical characteristics, such as color or shape.
Another example of a structural adaptation occurs in many desert plants. Some types of cactus plants have spines. Spines are leaves that are reduced in size. The adaptation of smaller leaves helps reduce water loss in a dry environment.
Functional AdaptationsFunctional adaptations involve internal systems that
affect an organism’s physiology or biochemistry. For example, the alpine snowbell, a flower species, has adapted to survive in an environment with a short growing season.
In the high altitude of the mountains, where the alpine snowbell grows, light and temperature conditions for flowering are favorable for only a short period during the summer. The alpine snowbell produces flower buds at the end of the previous season. Over the winter, the buds remain dormant—alive, but not actively growing. In the spring, increased light triggers the plant to bloom even when it is still surrounded by snow. These adaptations enable the species to survive.
Behavioral AdaptationsMigration, and other behavioral adaptations, involve the
ways an organism behaves or acts. For example, caribou migrate south for the winter. Other animals, such as birds, whales, and butterflies, also migrate. Animal species that migrate to find adequate food and suitable temperatures survive and reproduce more successfully.
Key Concept Check5. Describe three types of adaptations.
Reading Check3. Identify How can a species benefit from an adaptation?
4. Hypothesize How might a monkey’s long tail be an example of a structural adaptation?
Reading Essentials Heredity and How Traits Change 413
C210_015_020_RE_L3_889406.indd 17C210_015_020_RE_L3_889406.indd 17 2/19/10 4:36:51 PM2/19/10 4:36:51 PM
Copyrig
ht ©
Glen
coe/M
cGraw
-Hill, a d
ivisio
n o
f The M
cGraw
-Hill C
om
pan
ies, Inc.
Evolution of Populations—Why Traits Change
Once an inherited trait has become more frequent in a population, the population has adapted and evolved. Evolution is change over time. Evolution by natural selection is a way that populations change over time. When populations evolve, species can look and behave differently than their ancestors. This happens because the frequency of genetic traits changes over time. As the environment changes, different inherited traits might enable survival, and the population can evolve again.
A Modern Example of Change Over TimeBacteria can cause infections in your body, such as strep
throat or pneumonia. Sometimes a doctor might prescribe an antibiotic to help you fight an infection. Antibiotics are drugs that kill bacteria. Although antibiotics often kill bacteria effectively, variation exists within a population of bacteria. As shown in the figure below, some bacteria in a population might have a mutation that lets them survive when exposed to an antibiotic. When the surviving bacteria reproduce, that trait passes to their offspring. Soon, most individuals in the population survive when exposed to the antibiotic. Bacteria that survive when exposed to an antibiotic are called antibiotic-resistant. Antibiotic-resistant bacteria have caused deadly infections and are of great concern to scientists.
Visual Check7. Draw a circle around the dish with the largest number of resistant bacteria.
ACADEMIC VOCABULARYsurvive(verb) to remain alive
Key Concept Check6. State Why do traits change over time?
Antibiotic Resistance in Bacteria
Antibiotic
Resistant bacteria
Nonresistant bacteriaNew resistant and
nonresistant bacteria
are treated with the
same antibiotic.
An antibiotic is added to a population
of bacteria. A few of the bacteria
already have mutations that enable
them to resist the antibiotic.
The antibiotic kills most of
the nonresistant bacteria.
The surviving bacteria
reproduce.
The antibiotic now affects only a
small percentage of the bacteria.
The surviving bacteria continue
to reproduce. Most of the
bacteria are resistant to the
antibiotic.
414 Heredity and How Traits Change Reading Essentials
C210_015_020_RE_L3_889406.indd 18C210_015_020_RE_L3_889406.indd 18 2/19/10 4:37:00 PM2/19/10 4:37:00 PM
Copyri
ght
© G
lenco
e/M
cGra
w-H
ill,
a d
ivis
ion o
f T
he
McG
raw
-Hil
l C
om
pan
ies,
Inc.
Extinction and Conservation BiologyYou already have read that for evolution by natural
section to occur, variation within a population is needed. A population with diversity can survive changes in its environment and persist through time. But what happens when a population lacks variation among its individuals and the environment changes? The population might lose its ability to reproduce successfully and fail to survive. When the last individual of a species dies, the species has undergone extinction.
Today, many species are threatened with extinction. A species’ habitat might have been altered or destroyed. Some species have been hunted to extinction. For others, new species introduced into many habitats make it difficult for some native species to survive and reproduce.
A relatively new field of science focuses on saving species. Conservation biology is a branch of biology that studies why many species are in trouble and what can be done to save them. Sometimes scientists’ knowledge of genetics helps species that are in danger of extinction. For example, by 1995, the population of Florida panthers was between 20 and 30 individuals. The population had lost much of its natural variation and was struggling to survive.
Fortunately, scientists’ understanding of genetics and heredity saved the population from extinction. Scientists introduced into the Florida population several female panthers from a population in Texas. This was done to increase genetic diversity in the Florida population. By 2003, the Florida panther population had increased to 80 individuals, and the effort was considered a success.
8. Name one animal species that is in danger of becoming extinct.
Reading Check9. Explain Why did scientists introduce panthers from Texas into the Florida panther population?
SCIENCE USE V. COMMON USEintroduceScience Use to bring a substance or organism into a habitat or a population
Common Use to make someone known to others
Reading Essentials Heredity and How Traits Change 415
C210_015_020_RE_L3_889406.indd 19C210_015_020_RE_L3_889406.indd 19 2/19/10 4:37:06 PM2/19/10 4:37:06 PM
Copyrig
ht ©
Glen
coe/M
cGraw
-Hill, a d
ivisio
n o
f The M
cGraw
-Hill C
om
pan
ies, Inc.
Mini Glossary
Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
What do you think
END OF LESSON
Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.
ConnectED
adaptation: an inherited trait that increases an organism’s
chance of surviving and reproducing in a particular
environment
conservation biology: a branch of biology that studies
why many species are in trouble and what can be done
to save them
evolution: change over time
extinction: occurs when the last individual of a species dies
natural selection: the process by which individuals with
variations that help them survive in their environment live
longer, compete better, and reproduce more than those
individuals without these variations
variation: a slight difference in inherited traits among
individuals in a population
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that explains the difference between an adaptation and a variation.
2. Use the graphic organizer below to identify three factors that contribute to extinction.
3. An environment supports a species of beetle. Some beetles are green, some brown. Because of a drought, birds see green beetles and eat them more often than brown beetles. Over time, which color would you expect to become more common? Why?
Extinction
416 Heredity and How Traits Change Reading Essentials
C210_015_020_RE_L3_889406.indd 20C210_015_020_RE_L3_889406.indd 20 2/19/10 4:37:09 PM2/19/10 4:37:09 PM
A column in the
periodic table is
called a group.
A row in the
periodic table is
called a period.
The number in parentheses is the mass number of the longest lived isotope for that element.
PERIODIC TABLE OF THE ELEMENTS
Gas
Liquid
Solid
Synthetic
1
2
93 4 5 6 7
1
2
3
4
5
6
7
Lanthanide series
Actinide series
8
Thorium
90
Th232.04
Cerium
58
Ce140.12
Protactinium
91
Pa231.04
Praseodymium
59
Pr140.91
Uranium
92
U238.03
Neodymium
60
Nd144.24
Neptunium
93
Np(237)
Promethium
61
Pm(145)
Plutonium
94
Pu(244)
Samarium
62
Sm150.36
Americium
95
Am (243)
Europium
63
Eu151.96
Francium
87
Fr(223)
Cesium
55
Cs132.91
Rubidium
37
Rb85.47
Potassium
19
K39.10
Sodium
11
Na22.99
Lithium
3
Li6.94
Hydrogen
1
H1.01
Radium
88
Ra(226)
Barium
56
Ba137.33
Strontium
38
Sr87.62
Calcium
20
Ca40.08
Magnesium
12
Mg24.31
Beryllium
4
Be9.01
Actinium
89
Ac(227)
Lanthanum
57
La138.91
Yttrium
39
Y88.91
Scandium
21
Sc44.96
Rutherfordium
104
Rf(267)
Hafnium
72
Hf178.49
Zirconium
40
Zr91.22
Titanium
22
Ti47.87
Dubnium
105
Db(268)
Tantalum
73
Ta180.95
Niobium
41
Nb92.91
Vanadium
23
V50.94
Seaborgium
106
Sg(271)
Tungsten
74
W183.84
Molybdenum
42
Mo95.96
Chromium
24
Cr52.00
Bohrium
107
Bh(272)
Rhenium
75
Re186.21
Technetium
43
Tc(98)
Manganese
25
Mn54.94
Hassium
108
Hs(270)
Osmium
76
Os190.23
Ruthenium
44
Ru101.07
Iron
26
Fe55.85
Meitnerium
109
Mt(276)
Iridium
77
Ir192.22
Rhodium
45
Rh102.91
Cobalt
27
Co58.93
Hydrogen
1
H1.01
Element
Atomic number
Symbol
Atomic mass
State ofmatter
ES1_ES2_RE_SE_BC.indd 2ES1_ES2_RE_SE_BC.indd 2 3/13/10 6:42:26 PM3/13/10 6:42:26 PM
10 11 12
13 14 15 16 17
18
The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified.*
Metal
Metalloid
Nonmetal
Recently discovered
Curium
96
Cm(247)
Gadolinium
64
Gd157.25
Berkelium
97
Bk(247)
Terbium
65
Tb158.93
Californium
98
Cf(251)
Dysprosium
66
Dy162.50
Einsteinium
99
Es(252)
Holmium
67
Ho164.93
Fermium
100
Fm(257)
Erbium
68
Er167.26
Mendelevium
101
Md(258)
Thulium
69
Tm168.93
Nobelium
102
No(259)
Ytterbium
70
Yb173.05
Lawrencium
103
Lr(262)
Lutetium
71
Lu174.97
Darmstadtium
110
Ds(281)
Platinum
78
Pt195.08
Palladium
46
Pd106.42
Nickel
28
Ni58.69
Roentgenium
111
Rg(280)
Gold
79
Au196.97
Silver
47
Ag107.87
Copper
29
Cu63.55
Copernicium
112
Cn(285)
Mercury
80
Hg200.59
Cadmium
48
Cd112.41
Zinc
30
Zn65.38
Ununtrium
113
Uut(284)
*
Thallium
81
Tl204.38
Indium
49
In114.82
Gallium
31
Ga69.72
Aluminum
13
Al26.98
Boron
5
B10.81
Ununquadium
114
Uuq(289)
*
Lead
82
Pb207.20
Tin
50
Sn118.71
Germanium
32
Ge72.64
Silicon
14
Si28.09
Carbon
6
C12.01
Ununpentium
115
Uup(288)
*
Bismuth
83
Bi208.98
Antimony
51
Sb121.76
Arsenic
33
As74.92
Phosphorus
15
P30.97
Nitrogen
7
N14.01
Ununhexium
116
Uuh(293)
*
Polonium
84
Po(209)
Tellurium
52
Te127.60
Selenium
34
Se78.96
Sulfur
16
S32.07
Oxygen
8
O16.00
Astatine
85
At(210)
Iodine
53
I126.90
Bromine
35
Br79.90
Chlorine
17
Cl35.45
Fluorine
9
F19.00
Ununoctium
118
Uuo(294)
*
Radon
86
Rn(222)
Xenon
54
Xe131.29
Krypton
36
Kr83.80
Argon
18
Ar39.95
Neon
10
Ne20.18
Helium
2
He4.00
ES1_ES2_RE_SE_BC.indd 3ES1_ES2_RE_SE_BC.indd 3 3/13/10 6:42:31 PM3/13/10 6:42:31 PM
A column in the
periodic table is
called a group.
A row in the
periodic table is
called a period.
The number in parentheses is the mass number of the longest lived isotope for that element.
PERIODIC TABLE OF THE ELEMENTS
Gas
Liquid
Solid
Synthetic
1
2
93 4 5 6 7
1
2
3
4
5
6
7
Lanthanide series
Actinide series
8
Thorium
90
Th232.04
Cerium
58
Ce140.12
Protactinium
91
Pa231.04
Praseodymium
59
Pr140.91
Uranium
92
U238.03
Neodymium
60
Nd144.24
Neptunium
93
Np(237)
Promethium
61
Pm(145)
Plutonium
94
Pu(244)
Samarium
62
Sm150.36
Americium
95
Am (243)
Europium
63
Eu151.96
Francium
87
Fr(223)
Cesium
55
Cs132.91
Rubidium
37
Rb85.47
Potassium
19
K39.10
Sodium
11
Na22.99
Lithium
3
Li6.94
Hydrogen
1
H1.01
Radium
88
Ra(226)
Barium
56
Ba137.33
Strontium
38
Sr87.62
Calcium
20
Ca40.08
Magnesium
12
Mg24.31
Beryllium
4
Be9.01
Actinium
89
Ac(227)
Lanthanum
57
La138.91
Yttrium
39
Y88.91
Scandium
21
Sc44.96
Rutherfordium
104
Rf(267)
Hafnium
72
Hf178.49
Zirconium
40
Zr91.22
Titanium
22
Ti47.87
Dubnium
105
Db(268)
Tantalum
73
Ta180.95
Niobium
41
Nb92.91
Vanadium
23
V50.94
Seaborgium
106
Sg(271)
Tungsten
74
W183.84
Molybdenum
42
Mo95.96
Chromium
24
Cr52.00
Bohrium
107
Bh(272)
Rhenium
75
Re186.21
Technetium
43
Tc(98)
Manganese
25
Mn54.94
Hassium
108
Hs(270)
Osmium
76
Os190.23
Ruthenium
44
Ru101.07
Iron
26
Fe55.85
Meitnerium
109
Mt(276)
Iridium
77
Ir192.22
Rhodium
45
Rh102.91
Cobalt
27
Co58.93
Hydrogen
1
H1.01
Element
Atomic number
Symbol
Atomic mass
State ofmatter
ES1_ES2_RE_SE_BC.indd 2ES1_ES2_RE_SE_BC.indd 2 3/13/10 6:42:26 PM3/13/10 6:42:26 PM
10 11 12
13 14 15 16 17
18
The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified.*
Metal
Metalloid
Nonmetal
Recently discovered
Curium
96
Cm(247)
Gadolinium
64
Gd157.25
Berkelium
97
Bk(247)
Terbium
65
Tb158.93
Californium
98
Cf(251)
Dysprosium
66
Dy162.50
Einsteinium
99
Es(252)
Holmium
67
Ho164.93
Fermium
100
Fm(257)
Erbium
68
Er167.26
Mendelevium
101
Md(258)
Thulium
69
Tm168.93
Nobelium
102
No(259)
Ytterbium
70
Yb173.05
Lawrencium
103
Lr(262)
Lutetium
71
Lu174.97
Darmstadtium
110
Ds(281)
Platinum
78
Pt195.08
Palladium
46
Pd106.42
Nickel
28
Ni58.69
Roentgenium
111
Rg(280)
Gold
79
Au196.97
Silver
47
Ag107.87
Copper
29
Cu63.55
Copernicium
112
Cn(285)
Mercury
80
Hg200.59
Cadmium
48
Cd112.41
Zinc
30
Zn65.38
Ununtrium
113
Uut(284)
*
Thallium
81
Tl204.38
Indium
49
In114.82
Gallium
31
Ga69.72
Aluminum
13
Al26.98
Boron
5
B10.81
Ununquadium
114
Uuq(289)
*
Lead
82
Pb207.20
Tin
50
Sn118.71
Germanium
32
Ge72.64
Silicon
14
Si28.09
Carbon
6
C12.01
Ununpentium
115
Uup(288)
*
Bismuth
83
Bi208.98
Antimony
51
Sb121.76
Arsenic
33
As74.92
Phosphorus
15
P30.97
Nitrogen
7
N14.01
Ununhexium
116
Uuh(293)
*
Polonium
84
Po(209)
Tellurium
52
Te127.60
Selenium
34
Se78.96
Sulfur
16
S32.07
Oxygen
8
O16.00
Astatine
85
At(210)
Iodine
53
I126.90
Bromine
35
Br79.90
Chlorine
17
Cl35.45
Fluorine
9
F19.00
Ununoctium
118
Uuo(294)
*
Radon
86
Rn(222)
Xenon
54
Xe131.29
Krypton
36
Kr83.80
Argon
18
Ar39.95
Neon
10
Ne20.18
Helium
2
He4.00
ES1_ES2_RE_SE_BC.indd 3ES1_ES2_RE_SE_BC.indd 3 3/13/10 6:42:31 PM3/13/10 6:42:31 PM