splash contents chapter introduction multiple lines of evidence 19.1fossil evidence 19.2evidence...
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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
ChapterMenu
A Cite evidence from fossils, ecology, and homologies that support the theory of evolution.
Learning Outcomes
By the end of this chapter you will be able to:
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.
Why do scientists need to use different lines of evidence to understand evolution?
Changes in Species How does evolution
account for the appearance of new species and the disappearance of other species?
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.
• The idea of biological evolution did not start or end with Charles Darwin’s publication of The Origin of Species in 1859.
Multiple Lines of Evidence
19.1 Fossil Evidence
• 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.
• Evolution is one of the most important ideas in biology and is supported by a large body of evidence.
19.1 Fossil Evidence (cont.)
• 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
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
(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.
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
Some extinct animals:(a) Eryops, living approximately 280 million years ago, was one of the first air-
breathing 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.
• 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.
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
19.1 Fossil Evidence (cont.)
Multiple Lines of Evidence
(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.
• Direct observations of modern, living species show how species are related and how natural selection acts on inherited variation to change species.
19.2 Evidence from Ecology and Homologies
• 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.)
Multiple Lines of Evidence
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.
• Evidence of coevolution is often found in the adaptations of predators and their prey.
• Many symbiotic species have coevolved to the point that neither can survive without the other.
19.2 Evidence from Ecology and Homologies (cont.)
Multiple Lines of Evidence
• 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.
19.2 Evidence from Ecology and Homologies (cont.)
Multiple Lines of Evidence
• 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.
19.2 Evidence from Ecology and Homologies (cont.)
Multiple Lines of Evidence
• Homologies also help biologists understand the history of evolutionary changes.
• 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.
19.2 Evidence from Ecology and Homologies (cont.)
Multiple Lines of Evidence
• The study of genetics has provided fundamental support for the theory of evolution.
19.3 Genetic and Molecular Evidence
• 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
• 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.
19.3 Genetic and Molecular Evidence (cont.)
Multiple Lines of Evidence
– Evolutionary theory predicts pseudogenes accumulate mutations faster than functional genes in the same family.
• 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.
19.3 Genetic and Molecular Evidence (cont.)
Multiple Lines of Evidence
• 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.
19.3 Genetic and Molecular Evidence (cont.)
Multiple Lines of Evidence
• 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.
19.3 Genetic and Molecular Evidence (cont.)
Multiple Lines of Evidence
19.3 Genetic and Molecular Evidence (cont.)
Multiple Lines of Evidence
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.
• Speciation is the appearance of a new species.
Origin of Species
19.4 The Process of Speciation
• 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.
• 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.)
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.
• Ecological isolation occurs when two populations adapt to different habitats.
Origin of Species
19.4 The Process of Speciation (cont.)
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.
• 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.)
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.
• 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
19.4 The Process of Speciation (cont.)
• Adaptive radiation is a rapid increase in speciation from a common ancestor.
19.5 Patterns in Evolution
– 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.
Origin of Species
• The great numbers of species in groups such as the insects, mammals, and the grass and lily families reflect a history of adaptive radiation.
19.5 Patterns in Evolution (cont.)
Origin of Species
• 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.
19.5 Patterns in Evolution (cont.)
Origin of Species
This Australian lungfish (Neoceratodus), a “living fossil”, has changed little in millions of years.
19.5 Patterns in Evolution (cont.)
Origin of Species
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).
• 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.
19.5 Patterns in Evolution (cont.)
Origin of Species
– 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.
Summary
• 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.
• 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.
Summary (cont.)
• 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.
• Isolating mechanisms speed up the process of speciation. Geographic, ecological, behavioral, seasonal, and mechanical isolation all occur and function in natural populations.
Summary (cont.)
• 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.
• 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.
Reviewing Key TermsMatch the term on the left with the correct description.
___ paleontology
___ coevolution
___ pseudogene
___ speciation
___ polyploidy
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
b
a
e
c
d
Reviewing Ideas1. 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 Ideas2. 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 Concepts3. 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 Concepts4. 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.
Synthesize5. 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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