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PowerLecture:
Chapter 24
Principles of Evolution
Learning Objectives




Understand how variation occurs in
populations and how changes in allele
frequencies can be measured.
Know how mutations, gene flow, genetic
drift, and natural selection can influence the
rate and direction of population change.
Describe the types of selection mechanisms
that help shape populations.
Characterize the mechanisms of isolation
that promote speciation.
Learning Objectives (cont’d)


Be able to cite what biologists generally
accept as evidence to support concepts of
evolution. Explain how observations from
comparative morphology and comparative
biochemistry are used to reconstruct the
past.
Describe how life might have spontaneously
arisen on Earth approximately 3.5 billion
years ago.
Learning Objectives (cont’d)



Understand the general physical features
and behavioral patterns attributed to early
primates. Know their relationship to other
mammals.
Trace primate evolutionary development.
Understand the distinction between
hominoid and hominid.
Impacts/Issues
Measuring Time
Measuring Time
How do we measure time?



In geologic time we recognize
that asteroids from the
beginning of the universe are
still orbiting the sun.
About 65 million years ago one
of these asteroids hit Earth,
causing the extinction of the
dinosaurs and other forms of
life.
Measuring Time
Humanlike species were evolving in Africa
about 5 million years ago.



Modern humans have been around for about
100,000 years.
Change could occur in the future, especially if
the large asteroid predicted for 2028 happens
to sweep a bit too close to Earth.
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 A large
asteroid impact could obliterate
civilization and much of Earth’s biodiversity.
Should we spend millions, even billions, of
dollars to search for and track asteroids?


a. Yes, even though the chance of impact is low,
stakes are high. With warning, we can minimize
damage.
b. No, the likelihood of an impact is very low and
the cost is high, so it is not worth it.
Section 1
A Little Evolutionary History
A Little Evolutionary History
Evolution is defined by biologists as
genetic change in a line of descent through
successive generations.



In the 1800s, the source of Earth’s amazing
diversity of life forms was a matter of dispute.
The prevailing belief in creation was being
challenged by evidence supplied from new
investigatory tools in the fields of geology and
comparative anatomy.
A Little Evolutionary History
In 1831, botanist John Henslow arranged
for a 22-year-old Charles Darwin to take
ship as a naturalist aboard the HMS Beagle.



Throughout the trip, Darwin studied and
collected a variety of plants and animals.
Darwin returned after
five years at sea and
with other scientists
began pondering the
growing evidence that
life forms change over time.
Figure 24.1
route of
Beagle
EQUATOR
Galápagos
Islands
Fig 24.1a(1), p 444
A Little Evolutionary History
Thomas Malthus had suggested that as a
population outgrows its resources, its
members must compete for what is
available; some will not make it.



Darwin’s observations found support for this
idea in nature; chance could be part of the
equation, but so was the variation of traits
among members of the same species.
Darwin’s work eventually led to the proposal of
natural selection; decades later, genetics
would provide understanding of how those traits
could vary in the first place.
Section 2
A Key Evolutionary Idea:
Individuals Vary
A Key Evolutionary Idea: Individuals Vary
Evolution has two major components:



Microevolution refers to the cumulative
genetic changes that give rise to new species.
Macroevolution applies to the large-scale
patterns, trends, and rates of change among
groups of species.
A Key Evolutionary Idea: Individuals Vary
Individuals don’t evolve—populations do.


Evolution occurs only where there is change in
the genetic makeup of a population.
•
•
•
A population is a group of individuals belonging to
the same species, occupying the same given area.
Members of a population demonstrate certain
morphological, physiological, and behavioral traits in
common.
Populations exhibit
immense variation
among their
individual members.
Figure 24.2
A Key Evolutionary Idea: Individuals Vary
Variation comes from genetic differences.



All of the genes of a population make up the
gene pool, but the genes have slightly different
forms called alleles.
Variations in traits in a population result when
individuals inherit different combinations of
alleles.
Figure 24.3
Section 3
Microevolution:
How New Species Arise
Microevolution:
How New Species Arise
Mutation produces new forms of genes.


Mutations are heritable changes in DNA and
are the only source of new gene forms.
•
•

Mutations are rare events.
Whether they are harmful (lethal mutation), neutral,
or beneficial depends on how the altered gene
product performs under prevailing conditions.
The majority of mutations are probably harmful,
altering traits in such a way that an individual
cannot survive or reproduce.
Microevolution:
How New Species Arise
Natural selection can reshape the genetic
makeup of a population.


The theory of evolution by natural selection
proposed by Darwin has several major points:
•
•
•
Individuals of a population vary in form, functioning,
and behavior.
Many variations can be passed from generation to
generation.
Some forms of a trait are more advantageous than
others; they improve chances of surviving and
reproducing.
Microevolution:
How New Species Arise
•
•
•

Natural selection is the difference in survival and
reproduction that occurs among individuals differing
in one or more traits.
A population is evolving when some forms of a trait
are increasing/decreasing, indicating changes in the
commonality of the alleles.
Over time, shifts in the makeup of the gene pools
have generated Earth’s diverse life forms.
Adaptation describes the tendency for
organisms to come to have the characteristics
that suit them best to the conditions of their
environment.
Microevolution:
How New Species Arise
Chance can also change a gene pool.


Genetic drift is the random fluctuation in allele
frequencies over time due to chance
occurrences alone.
•
•
It is more rapid in small populations.
In the founder effect, a few individuals (carrying
genes that may/may not be typical of the whole
population) leave the original population to establish
a new one.
Microevolution:
How New Species Arise

In gene flow, genes move with the individuals
when they move out of, or into, a population.
•
•
The physical flow of alleles tends to minimize genetic
variation between populations.
It decreases the effects of mutation, genetic drift, and
natural selection.
The ability to interbreed defines a species.


A species is one or more populations of
individuals who can interbreed under natural
conditions and produce fertile offspring.
Microevolution:
How New Species Arise

Populations of one species are reproductively
isolated from other populations.
•
•
•
Reproductive isolation is the stoppage of gene flow
between two populations.
In geographic isolation, barriers restrict gene flow
between populations.
Reproductive isolating mechanisms include isolation
of gametes, structural isolation, isolation in time,
unworkable hybrids, and behavioral isolation.
Microevolution:
How New Species Arise

Divergence is the process whereby local units
of a population become reproductively isolated
from other units and thus experience changes
in gene frequencies between them, which may
be enough to halt interbreeding and lead to
speciation.
Figure 24.4
time A
time B time C
time D
daughter
species
daughter
species
parent species
time
Fig 24.4a, p.447
Microevolution:
How New Species Arise
Speciation can occur gradually or in
“bursts.”



According to the gradualism model, new
species emerge through many small changes in
form over long spans of time.
In the punctuated equilibrium model, most
evolutionary changes occur in bursts.
Section 4
Looking at Fossils
and Biogeography
Looking at Fossils and Biogeography
A fossil is recognizable physical evidence
of ancient life.
Fossils are found in sedimentary rock.

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
The most common fossils are bones, teeth,
shells, seeds, and the other hard parts of
different organisms.
Figures 24.5 and 24.6
Looking at Fossils and Biogeography

Fossilization begins with burial in sediments or
volcanic ash.
•
•
•

Water invades, depositing ions and inorganic
compounds.
Pressure from accumulating sediments transforms
the trapped material into stony fossils.
Organisms are most likely to be preserved when
they are buried rapidly and in the absence of oxygen.
Stratification is the layering of sedimentary
deposits formed over long geologic time.
Looking at Fossils and Biogeography
Completeness of the fossil record varies.


The fossil record is incomplete: large-scale
movements in the Earth’s crust have obliterated
evidence from crucial periods, and soft-bodied
organisms decayed rather than fossilized.
•
•

Population densities and body size further skew the
record.
The fossil record is also heavily biased toward
certain environments.
Radiometric dating tracks the radioactive
decay of isotopes trapped in sediments to allow
scientists to date the fossils they do find.
Looking at Fossils and Biogeography
Biogeography provides other clues.


Biogeography addresses the question of why
certain species occur where they do on the
surface of the earth.
•
•

The simplest explanation is that they evolved there
from ancestral species.
Alternatively, they may have dispersed there from
someplace else.
The study of plate tectonics reveals that the
continents once formed a giant supercontinent
called Pangea, thus shedding light on the
possible dispersal routes for different species.
EURASIAN
PLATE
NORTH
AMERICAN
PACIFIC PLATE
PLATE
COCOS
PLATE
NAZCA
PLATE
PACIFIC
PLATE
SOUTH
AMERICAN
PLATE
SOMALI
PLATE
AFRICAN
PLATE
PHILLIPINE
PLATE
INDOAUSTRALIAN
PLATE
ANTARCTIC PLATE
© 2007 Thomson Higher Education
Fig 24.7a, p.449
420 mya
260 mya
65 mya
10 mya
Fig 24.7b, p.449
Section 5
Comparing the Form and
Development of Body Parts
Comparing the Form and
Development of Body Parts
Comparing body forms may reveal
evolutionary connections.


Through comparative morphology,
researchers reconstruct evolutionary history on
the basis of information contained in the
observed patterns of body form.
•
•
Homologous structures are the same body
features that have become modified in different lines
of descent from common ancestors (morphological
divergence).
One example of this would be the bones in the
forelimbs of vertebrates.
4
3
a. early reptile
21
5
21
3
4
b. pterosaur
1
c. chicken
2
3
1
2
d. bat
3 4
1
5
e. porpoise
2
4
3
5
f. penguin
2
1
3
4
2
3
g. human
5
Fig 24.8, p.450
Comparing the Form and
Development of Body Parts


Analogous structures are used for similar
functions in similar environments by dissimilar
and distantly related species.
Morphological convergence is the adoption of
similar form and function over periods of time
(example: the distinctive torsos of dolphins and
tuna).
Comparing the Form and
Development of Body Parts
Development patterns also provide clues.


Different organisms may show similarities
in morphology during their embryonic stages;
these similarities often indicate evolutionary
relationships.
•
•
Some of the variation seen in adult vertebrates is
due to mutations in regulatory genes that control the
rates of growth of different body parts.
One example can be seen in chimpanzees and
humans; as infants skull structure is virtually
identical, but adults have very different appearances.
fish
reptile
bird (chicken)
mammal (human)
Fig 24.9a, p 451
fish
reptile
bird (chicken)
mammal (human)
Stepped Art
Fig 24.9a, p 451
adult
shark
© 2007 Thomson Higher Education
human
embryo
(three
millimeters
long)
Fig 24.9b, p 451
infant
adult
a. Chimpanzee skull
infant
adult
b. Human skull
Fig 24.10, p 451
Comparing the Form and
Development of Body Parts

Vestigial structures are apparently useless
structures that are left over from a time when
more functional versions were important for an
ancestor.
backbone
(vertebral
column)
pelvic girdle
(hind legs
attach to these)
coccyx (bones
where many
other mammals
have a tail)
small bone
attached to
pelvic girdle
thighbone
attached to
pelvic girdle
Fig. 24.11, p.451
Section 6
Comparing Biochemistry
Comparing Biochemistry


Genes and gene products
(proteins) of different species
contain information about
evolutionary relationships.
By comparing body form, for
example, all primates appear to
be related; this can be
confirmed or denied based on
analysis of the amino acid
sequences in proteins.
Figure 24.15a-b
Comparing Biochemistry


The degree of similarity of amino acid
sequences is a measure of species
relatedness; fewer differences indicate a closer
relationship and vice versa.
Cytochrome c is an example of a protein that
has changed very little over time; in humans
and chimps, the sequence is identical, but there
are 19 amino acid differences between humans
and turtles.
Comparing Biochemistry

Nucleotide sequences can also be analyzed
for neutral mutations, which provide
information on variation over time;
calculations of neutral mutations can give
an indication of “when” species divergence
occurred—a molecular clock.
Section 7
How Species
Come and Go
How Species Come and Go
Extinction is the irrevocable loss of a
species.




Background extinction is the steady rate of
species disappearance over time as local
conditions change.
Mass extinction is the disappearance of major
groups of species on a global scale due to
catastrophic events.
Human activities have led to an increase in the
extinction rate in the past few centuries.
How Species Come and Go
In adaptive radiation, new species arise.


In adaptive radiation, new species move into
new habitats during bursts of microevolution.
•
•

Many adaptive radiations have occurred in the first
few million years following major mass extinction
events.
Mammals, for example, arose and radiated into the
habitats vacated by extinction of the dinosaurs.
Adaptive radiations have also occurred in
humans; Homo erectus radiated away from
Homo habilis some 2 million years ago and
eventually gave rise to Homo sapiens about
100,000 years ago.
1.8 meters (6 feet)
thighbone
(femur)
shinbone
(tibia)
Neandertal
Modern Inuit
Homo erectus
Modern Masai
Fig 24.12., p.452
0.2%
0.1%
0% = genetic distance
New Guinea, Australia
Pacific Islands
Southeast Asia
Arctic, Northeast Asia
North, South America
Northeast Asia
Europe, Middle East
Africa
Proposed Family Tree for Homo Sapiens
Fig 24.13, p.453
Artificial Selection
Figures 24.25 and 24.26
Section 8
Endangered Species
Endangered Species


Human activities are
driving many species
to extinction.
An endangered
species is an
endemic species that
is very vulnerable to extinction; endemic
species are those found only in one region
of the world and nowhere else.
Figure 24.14
Endangered Species



Habitat loss is the major threat to more than
90% of the endangered species.
Introduction of exotic species is also displacing
endemic species.
Human trade in animals and animal parts also
claims a large toll.
Figure 24.24
Section 9
Evolution from a
Human Perspective
Evolution from a Human Perspective
All forms of life can be classified and
grouped for greater ease in understanding
their evolutionary relationships.



The binomial system of nomenclature used two
names—genus and species—to identify each
distinct organism.
Modern systems use several groupings to
organize the genera (from the broadest
grouping down to the most specific grouping):
domain, kingdom, phylum, class, order, family,
genus, and species.
Evolution from a Human Perspective
Five trends mark human evolution.


Precision grip and power grip.
•
•
•
Prehensile movements allowed fingers to wrap
around objects in a grasp.
Opposable thumb and fingers allowed more refined
use of the hand.
The precision grip and power grip movements of
the human hand allowed for tool making.
Evolution from a Human Perspective


Improved daytime vision: resulted from forward
directed eyes (depth perception) with their
increased ability to discern shape, movement,
color, and light intensity.
Changes in dentition: resulted in humans
having smaller teeth of more
uniform length; generally the
jaws and teeth became less
specialized.
Jaw shape
and teeth of
an early
primate
Evolution from a Human Perspective

Changes in the brain and behavior.
•
•
The brain increased in size and complexity, resulting
in new behaviors.
Culture evolved; culture is composed of all the
behavior patterns that are passed between
generations by learning and symbolic behavior,
especially language.
human
chimp
gibbon
macaque
lemur
70
60
postreproductive
years
50
40
adult
30
20
10
subadult
infancy
18
24
30
34
38
time in uterus (weeks)
Fig 24.16, p.455
Evolution from a Human Perspective

Upright walking.
•
•
Bipedalism is the
habitual two-legged
gait characteristic of
humans.
Compared with
monkeys and apes,
humans have a
shorter, S-shaped,
somewhat flexible
backbone, which
works with shoulder
blades and pelvic
girdle to allow for
upright movement.
Figure 24.17
foramen
magnum
Fig 24.17b, p 455
foramen
magnum
Fig 24.17c, p 455
Section 10
Emergence of
Early Humans
Emergence of Early Humans
Apelike forms, the hominoids, spread
through Africa, Asia, and Europe between
23 and 5 million years ago.



At this time, the earth began to change and
most of the hominoids
went extinct.
One survivor was the
common ancestor of
both the great apes and
the first hominids.
Figure 24.18b-c
Emergence of Early Humans
Early hominids lived in Central Africa.



Sahelanthropus tchadensis was one of the
first species to evolve in Central Africa about 6
to 7 million years ago, during the time when the
ancestors of humans were becoming distinct
from the apes.
Australopithecus afarensis is one of the
species that walked upright across the African
plain some 3.7 million years ago.
Emergence of Early Humans
Is Homo sapiens “out of Africa”?


Species of humans appeared a little over 2
million years ago in eastern Africa; the earliest
humans were Homo habilis and Homo
rudolfensis.
•
•
They had increased brain size, a smaller face, and
thickly enameled teeth, which permitted a wider
variety of diet.
They also used tools.
H. habilis
1.9–1.6 million years
Fig 24.18d, p 456
Homo rudolfensis
2.4–1.8 million years
Fig 24.18e, p 456
Emergence of Early Humans

Divergence produced Homo erectus; these
early humans began migrating out of Africa into
Europe and Asia in waves.
•
•
Homo erectus still lived in Southeast Asia between
53,000 and 37,000 years ago.
Neanderthals lived as recently as 30,000 years ago
in Europe and the Near East, and their extinction
coincided with the origin of modern humans between
40,000 and 30,000 years ago.
Emergence of Early Humans
Where did Homo sapiens originate?


Two models are used to interpret the evidence
provided by measurements of small genetic
differences seen among humans today:
•
•
The multiregional model proposes that Homo
sapiens evolved from Homo erectus in the various
parts of the world to which it migrated many years
before; gene flow prevented speciation.
In the African emergence model, Homo sapiens
originated in Africa and migrated out to replace the
Homo erectus populations already there; various
lines of evidence support this model.
H. sapiens
fossil from Ethiopia,
160,000 years old
Fig 24.20b, p 457
40,000 years ago
15,000-30,000
years ago
60,000
years ago
160,000
years ago
35,000-60,000
years ago
Fig 24.20a, p.457
Section 11
Earth’s History and
the Origin of Life
Earth’s History and the Origin of Life

Primordial Earth was a hard place 4 billion
years ago, but within 200 million years life
had appeared on its surface.
Figure 24.21
Earth’s History and the Origin of Life
Conditions on early Earth were intense.




The early atmosphere was likely composed of
gaseous hydrogen, nitrogen, carbon monoxide,
and carbon dioxide; there likely was no oxygen
or water.
Cooling and solidification of the Earth’s crust
allowed water to condense and rain to fall,
creating early seas.
Organic materials and water were necessary
for the beginnings of life.
Earth’s History and the Origin of Life
Biological molecules paved the way for cells
to evolve.



The first living cells probably emerged around
3.8 billion years ago and resembled modern
anaerobic bacteria.
Prior to this first cell, however, chemical
evolution would have had to occur.
Figure 24.22a
membrane-bound proto-cells
living
cells
self-replicating system enclosed in a
selectively permeable, protective lipid sphere
DNA
RNA
formation of
protein-RNA systems,
evolution of DNA
enzymes and
other proteins
formation of
lipid spheres
spontaneous formation of lipids,
carbohydrates, amino acids, proteins,
nucleotides under abiotic conditions
Fig 24.23a, p.459
membrane-bound proto-cells
living
cells
self-replicating system enclosed in a
selectively permeable, protective lipid sphere
DNA
RNA
formation of
protein-RNA systems,
evolution of DNA
enzymes and
other proteins
formation of
lipid spheres
spontaneous formation of lipids,
carbohydrates, amino acids, proteins,
nucleotides under abiotic conditions
Stepped Art
Fig 24.23a, p.459
Earth’s History and the Origin of Life
Experiments give us ideas about how life
first arose on Earth.



Simulations of the conditions on early Earth
show how molecules such as amino acids,
glucose, ribose, deoxyribose, and other sugars
could have been produced.
How did complex compounds such as proteins
form?
•
•
One scenario of chemical synthesis proposes that
clay templates served as “enzymes” to favor bond
formation among chemicals.
Alternatively, complex compounds may have first
formed near deep-sea hydrothermal vents.
Earth’s History and the Origin of Life

Enzymes, ATP, and other molecules could have
assembled spontaneously in places where they
were in close physical proximity, which would
have promoted chemical interactions—the
beginnings of metabolic pathways.
From accumulated organic compounds emerged
replicating systems consisting of DNA, RNA,
proteins, and enzymes.



Perhaps RNA strands were capable of enzyme activity
(as has recently been demonstrated) and promoted
protein synthesis.
The first cells were probably membrane-bound sacs
containing nucleic acids that served as templates for
proteins.