Download BSCS Chapter 19

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Chapter Introduction
Multiple Lines of Evidence
19.1 Fossil Evidence
19.2 Evidence from Ecology and Homologies
19.3 Genetic and Molecular Evidence
Origin of Species
19.4 The Process of Speciation
19.5 Patterns in Evolution
Chapter Highlights
Chapter Animations
Learning Outcomes
By the end of this chapter you will be able to:
A Cite evidence from fossils, ecology, and
homologies that support the theory of evolution.
B Discuss the genetic and molecular evidence
for evolution.
C Discuss the isolation mechanisms that can
cause speciation.
D Describe patterns in evolution such as
punctuated equilibrium.
Changes in Species
 How does evolution
account for the appearance
of new species and the
disappearance of other
species?
 Why do scientists need to
use different lines of
evidence to understand
evolution?
This photo shows a casting of Archaeopteryx.
Changes in Species
• Despites the current diversity
in life, several lines of
evidence support the
conclusion that all life had
a common ancestor.
• Inherited variation in
populations gives some
organisms an improved
chance to survive and
reproduce.
• Evolution is long-term
change in inherited
characteristics.
This photo shows a casting of Archaeopteryx.
Multiple Lines of Evidence
19.1 Fossil Evidence
• The idea of biological evolution did not start or end
with Charles Darwin’s publication of The Origin of
Species in 1859.
• Charles Darwin stands out because his book
introduced evolution as a testable scientific theory.
• Scientists have expanded, refined, and retested the
theory of evolution to explain long-term changes in
biological species.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Evolution is one of the most important ideas in
biology and is supported by a large body of evidence.
• Evolution is an area of active research.
• Scientists are currently exploring the details of how
certain species are related, how molecules undergo
evolution, and how modern species are changing.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Evidence of evolution includes physical remains, or
fossils, that are the record of ancient organisms.
• The fossil record in different strata of the earth shows
the order of evolutionary change.
• Paleontology is the branch of biological science
that studies fossils.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Microfossils are examples of ancestral species
recorded in the fossil record that are related to
modern species.
• The hard parts of organisms, such as shells and
bones, are the most likely to be preserved.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Softer tissue sometimes makes
a fossil record if it leaves an
impression in soft mud that
hardens and is preserved.
• Occasionally, ancient insects
were completely preserved when
they were trapped in tree sap
that became amber.
(top) A leaf fossil impression of Pecopteris dates
back to the Pennsylvanian Period, approximately
300 million years ago.
(bottom) This sample of amber with trapped flies
and a cricket is approximately 35 million years old.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Around 250,000 species of fossil organisms have
been found which has helped scientists reconstruct
much of the history of life.
• Biologists estimate that fossils of only 1 in 10,000
extinct species have been discovered because most
dead organisms decay and do not become fossils.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Fossil evidence supports the theory of evolution in
a variety of ways.
– Fossils offer physical records of organisms not
found on Earth today.
– Comparisons of fossils from different time periods
helps scientists determine the ancestral
relationships of extinct and living species.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
Some extinct animals:
(a) Eryops, living approximately 280 million years ago, was one of the first airbreathing animals in a line that would give rise to amphibians.
(b) The Diatryma, living 38 to 2 million years ago, was a flightless bird that may
have gone extinct because small mammals ate their eggs.
(c) The Syndyoceras may be related to modern ruminants (cows and deer).
(d) The Megatherium was a ground sloth that went extinct about 11,000 years ago.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
• Extinctions occur much more often in modern times
than they did in the past due mostly to the huge
increase in human population.
• In some cases, fossils record organisms before and
after new species split off from older ones providing
evidence of the rate of evolutionary change.
• One of the most intriguing types of fossil evidence is
that of intermediate stages between species and
their ancestors.
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
(a) This shows a model of Sinornithosaurus millenii, a turkey-sized feathered
dinosaur whose fossilized remains were found in China. (b) Despite the
dinosaurlike claws, teeth, and tail, this fossil shows the highly advanced shoulder
girdle that allowed for flapping arms, a feature almost identical to that of
Archaeopteryx, the earliest known bird.
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
• Direct observations of modern, living species show
how species are related and how natural selection
acts on inherited variation to change species.
• Differences among closely related species often
reflect adaptations to different environments.
• Coevolution is the continuous adaptation of different
species to each other.
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
(cont.)
On some islands in the Galápagos, tortoises
must feed on cactus with tough lower stems.
These tortoises have flared saddleback shells.
The elevated anterior portion of the shell
allows this tortoise to raise its head high
enough to reach the edible cactus leaves.
On islands where the cacti do not have
tall, woody stems, tortoises without
saddleback shells can easily reach the
edible leaves.
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
• Evidence of coevolution is often found in the
adaptations of predators and their prey.
(cont.)
• Many symbiotic species have coevolved to the point
that neither can survive without the other.
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
• One of the strengths of the theory of evolution
is that it can be tested.
• Artificial selection works in the same manner as
natural selection but with deliberate choices by
the breeder.
(cont.)
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
• Controlled experiments can produce stronger
evidence and show how natural selection occurs.
• Around 1930, Lee R. Dice conducted an
experiment with mice and barn owls that showed
how attacks by predators can lead to changes in
protective coloration.
(cont.)
Multiple Lines of Evidence
19.2 Evidence from Ecology and Homologies
• Homologies also help biologists understand the
history of evolutionary changes.
(cont.)
• Any aspect of an organism can be compared to
other species in the search for homologies.
• Biologists have found that homologous genes are
responsible for the formation of the body plan and
organs even in very distantly related species.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence
• The study of genetics has provided fundamental
support for the theory of evolution.
• The sources of genetic variation include mutation
and the recombination of alleles in sexually
reproducing eukaryotes.
• Genetic variation is the raw material of evolution.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
• One kind of mutation that provides evidence of the
history of evolution is gene duplication.
– Duplication of a gene produces gene families—
multiple copies of nearly identical DNA sequences.
– Some of the copies, called pseudogenes, are
neither transcribed nor translated and therefore
not subjected to natural selection.
– Evolutionary theory predicts pseudogenes
accumulate mutations faster than functional
genes in the same family.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
• Molecular data provide detailed evidence of the
degree of relatedness between species.
• Scientists compare the amino-acid sequences of
homologous proteins and the nucleotide sequences
of homologous genes in different species for
similarities.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
• The role of evolution in human disease is a growing
focus of medical science.
• Widespread use of antibiotics for the past 50 years
has produced a selective pressure to favor the
previously rare resistant bacteria.
• This selection pressure has resulted in new
populations that are resistant to antibiotics.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
• Mutation is especially common in short repeated
nucleotide sequences called microsatellites which
may contribute to evolution by increasing genetic
variation.
• Microsatellites can act as genetic switches in
bacteria, keeping populations diverse and ensuring
that at least some members can survive under
changing conditions.
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
This transmission
electron micrograph
shows several cells of
Neisseria gonorrhoeae,
the bacterium that
causes the sexually
transmitted disease
gonorrhea (color added,
x30,000). A highly
mutable region of
microsatellite DNA
determines whether the
organism will cause
disease.
Origin of Species
19.4 The Process of Speciation
• Speciation is the appearance of a new species.
• Although most evolutionary change is too slow
to see, there are examples in which it has been
observed.
A new species of saltbush, Atriplex
robusta, appears to have evolved in
Utah since a highway was built in 1969.
The highway provided a habitat that
allowed two species to come together
and hybridize.
Origin of Species
19.4 The Process of Speciation (cont.)
• Artificial selection can speed up speciation.
– Triticale, a relatively new species of grain, has
been produced by crossing wheat and rye.
Origin of Species
19.4 The Process of Speciation (cont.)
• Genetic changes in populations indicate that
evolution is taking place.
• In a large population that is well adapted to its
environment, the frequency of alleles in a gene pool
is in a state of equilibrium.
• A variety of factors can, however, change the
equilibrium of a gene pool.
Origin of Species
19.4 The Process of Speciation (cont.)
• Speciation in sexually reproducing organisms occurs
when two populations become so different in their
genetic makeup that they can no longer interbreed.
• In most cases, a small population that is isolated
from the rest of its species develops into a new
species.
• Geographic isolation is the most common
mechanism that separates populations.
Origin of Species
19.4 The Process of Speciation (cont.)
The Kaibab squirrel, Sciurus kaibabensis (a), and the Abert’s squirrel,
Sciurus aberti (b), are related species. When they became geographically
isolated on opposite rims of the Grand Canyon, they began to develop
differences. Note the differences in coloration.
Origin of Species
19.4 The Process of Speciation (cont.)
• Ecological isolation occurs when two populations
adapt to different habitats.
The alder flycatcher, Empidonax alnorum (a), and the willow flycatcher,
Empidonax traillii (b), were once considered the same species until it was
noticed that their habitats are completely different, and they do not crossbreed.
Origin of Species
19.4 The Process of Speciation (cont.)
• Mating behavior and physical characteristics are
important in the reproductive success of some
organisms.
– In some cases, the gametes are not chemically
compatible.
– Differences in size of the organisms or in the size
or shape of their reproductive organs can also
prevent mating.
Origin of Species
19.4 The Process of Speciation (cont.)
• Behavioral isolation can occur among animal
populations.
– If the mating pattern of a small group of organisms
becomes different from that of the main group,
then they can become reproductively isolated.
– Eventually the groups become separate species.
Origin of Species
19.4 The Process of Speciation (cont.)
Leopard frogs formerly were considered all one species, Rana pipiens. Today,
however, biologists consider some of the populations to be separate species.
The three frogs pictured are from Massachusetts (a), Oklahoma (b), and
Arizona (c). Northern and southern leopard frogs do not mate with each other.
The intermediate forms of the leopard frog can and do mate with each other
and with both the northern and southern populations.
Origin of Species
19.4 The Process of Speciation (cont.)
• Seasonal isolation occurs in plants and animals if
the reproductive cycles are on different seasonal
schedules.
Origin of Species
19.4 The Process of Speciation (cont.)
• Isolation mechanisms can be classed as those that
occur prior to zygote formation and those that occur
after zygote formation.
– A prezygotic mechanism is when the gametes
never meet because of geographic isolation,
mismatched mating behavior, or seasonal
isolation.
– A postzygotic mechanism is the failure of the
zygote to develop normally, such as when the
parents are too different, even though mating
and fertilization have occurred.
Origin of Species
19.4 The Process of Speciation (cont.)
• Polyploidy, the duplication of chromosomes, often
causes a new species of plant to form.
– The offspring generally cannot mate successfully
with plants having the parental number of
chromosomes.
– They can reproduce asexually or often can
mate with other polyploid offspring to establish
a new species.
– More than half of known species of flowering
plants are polyploid and, in rare cases, animals
can be polyploid.
Origin of Species
19.5 Patterns in Evolution
• Adaptive radiation is a rapid increase in speciation
from a common ancestor.
– When a population enters a diverse environment
with few competing species, it often divides into
several smaller populations.
– These populations avoid competing with each
other by adapting to different habitats or by using
different resources in the same habitat.
– Over time each population can become a
new species.
Adaptive radiation in mammals
Origin of Species
19.5 Patterns in Evolution (cont.)
• The great numbers of species in groups such as the
insects, mammals, and the grass and lily families
reflect a history of adaptive radiation.
Origin of Species
19.5 Patterns in Evolution (cont.)
• In some cases, the rate of large-scale change
remains very slow for a long period.
• This condition, stasis, may occur because a
population or species is well adapted and its
environment remains stable.
This Australian lungfish (Neoceratodus),
a “living fossil”, has changed little in
millions of years.
Origin of Species
19.5 Patterns in Evolution (cont.)
The modern horseshoe “crab,” Limulus polyphemus, which is not a true crab,
has changed only slightly in appearance from its 250-million-year-old
ancestors. A comparison of these species shows how little change has
occurred. Paleolimulus avitus (a) from the Permian Period is about 250 million
years old. Limulus walchi (b) from the Jurassic Period is approximately 180
million years old. Limulus polyphemus, the modern species, is shown here as a
drawing (c) and in its natural habitat in the Gulf of Maine (d).
Origin of Species
19.5 Patterns in Evolution (cont.)
• Scientists are now studying two patterns of change:
– Gradualism refers to evolutionary change and
speciation that occur through accumulation of
many gradual and fairly constant changes.
– Punctuated equilibrium involves a short period
of rapid change just after a population becomes
isolated and forms a new species, after which the
process slows down and approaches stasis.
Two evolutionary patterns
Summary
• The theory of evolution provides a scientific explanation for
changes in species and the history of life on Earth. It is a
testable theory that is supported by fossil evidence.
• Additional evidence comes from observation of populations of
living organisms and from anatomical, molecular, and genetic
information.
• Populations, not individual organisms, evolve.
• Small isolated populations of organisms evolve much more
rapidly than large populations.
• Speciation occurs when variation within a population becomes
so great that subgroups no longer interbreed.
Summary (cont.)
• Isolating mechanisms speed up the process of speciation.
Geographic, ecological, behavioral, seasonal, and mechanical
isolation all occur and function in natural populations.
• Other types of isolating mechanisms include prevention of
gamete fusion, failure of hybrid zygotes to develop normally
and survive, and failure of hybrid offspring to reproduce.
• A large increase in the number of species that develop in
newly available habitats is called adaptive radiation.
• Anatomical and molecular data are used to estimate the rates
of evolution on different scales. Molecular evolution proceeds
at a more constant rate.
• Parts of proteins that are not functionally important accumulate
amino-acid changes at a faster rate than parts that are
essential for function.
Summary (cont.)
• In some very stable environments, small populations with little
competition appear to evolve more slowly than other species.
This situation can result in “living fossils” that closely resemble
very ancient predecessors.
• There is evidence for more than one pattern of evolution.
• Gradualism describes the steady accumulation of small
changes over time.
• Punctuated equilibrium suggests that long periods of
evolutionary stability are interspersed with brief periods of
rapid change.
Reviewing Key Terms
Match the term on the left with the correct description.
___
paleontology
b
___
coevolution
a
___
pseudogene
e
___
speciation
c
___
polyploidy
d
a. the evolution of two species
interacting with each other and
reciprocally influencing each
other’s adaptations
b. the branch of biology that studies
the fossil record
c. the origin of new species as a
result of evolutionary processes
d. a condition in which an organism
has more than two sets of
chromosomes
e. a nonfunctioning DNA segment
that is similar in sequence to a
functioning gene
Reviewing Ideas
1. What is punctuated equilibrium?
Punctuated equilibrium is a pattern of evolution
that involves a short period of rapid change just
after a population becomes isolated and forms a
new species, after which the process slows
down and approaches stasis.
Reviewing Ideas
2. What evidence is there to support the theory
adaptive radiation?
The great numbers of species in groups such as
the insects, mammals, and the grass and lily
families reflect a history of adaptive radiation.
Using Concepts
3. How can the fossil record help determine
the ancestral relationships of extinct and
living species?
Comparisons of fossils in younger, shallower rock
deposits and older, deeper rocks help scientists
determine the ancestral relationships of extinct
and living species.
Using Concepts
4. How is evolution playing a role in
human diseases?
Many strains of bacteria that once were killed by
antibiotics are now resistant. Widespread use of
antibiotics for the past 50 years has produced a
selective pressure to favor the previously rare
resistant bacteria. In the laboratory, scientists can
demonstrate this evolutionary process by gradually
increasing the exposure of bacteria to certain
antibiotics. This selection pressure results in a new
population that is resistant. Consequently, the
antibiotic removes most of the competition from the
new population.
Synthesize
5. How could human activities increase speciation
among animals?
As humans convert land from natural to human
uses, they fragment habitat and change the
environment on a local and global scale. These
changes can geographically and ecologically
isolate populations. The effects of human
activities, such as global warming, can also
cause behavioral isolation in populations.
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Chapter Animations
Adaptive radiation in mammals
Two evolutionary patterns
Adaptive radiation in mammals
Two evolutionary patterns
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