2. Chapter 7 Darwinian Evolution: Unit Hyperlinks
7.1 Darwin’s influences
7.2 Natural selection
7.3 Fossil record
7.4 Evidence for evolution
7.5 Populations are the units
7.6 Evolutionary mechanisms
7.7 Macroevolution
7.8 Geological record
7.9 Reproductive barriers
7.10 Speciation
7.11 Taxonomy
7.12 Phylogenetic trees
7.1 Darwin’s influences and experiences led him to publish his theory of evolution
7.2 Unequal reproductive success leads to natural selection
7.3 The fossil record provides important evidence for evolution
7.4 Much evidence for evolution is found in the natural world
7.5 Populations are the units of evolution
7.6 Evolution proceeds through several mechanisms
7.7 Macroevolution encompasses large-scale changes
7.8 The geological record ties together the history of Earth and its life
7.9 Species are maintained by reproductive barriers
7.10 Speciation can occur through various mechanisms
7.11 Taxonomy is the classification of life
7.12 Phylogenetic trees represent evolutionary history

3. The Earth is filled with a wide diversity of organisms.
7.1 Opening Questions: How to explain the unity and diversity of living things?
The Earth is filled with a wide diversity of organisms.
Yet there is also great unity among living things
List at least three examples of how living things can differ.
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Many students may have misconceptions about what energy is or how it powers living things. An initial question exercise can help students identify and rectify their own misconceptions. Revisit these questions as you progress through the material.
List at least three traits or processes that all living things have in common.

4. 7.1 November 24, 1859, is a landmark date in the history of biology
In 1859, British naturalist Charles Darwin published On the Origin of Species by Means of Natural Selection.
In the Origin of Species Darwin introduced the concepts of evolution and natural selection.
Figure 7.1-1h Darwin’s Cultural and Scientific Context–8 of 15
Figure 7.1-1o Darwin’s Cultural and Scientific Context–15 of 15

5. 7.1 Until the 1800s most scientists had a different view of life and species
In early history, most thought a young Earth held unrelated and unchanging species.
The discovery of fossils (1700s) first suggested that the Earth was very old and that species could change over time.
Aristotle believed
species were immutable.
Figure 7.1-1a Darwin’s Cultural and Scientific Context–1 of 15
Figure 7.8-2f Plate Tectonics–6 of 8
Darwinius
masillae fossil

6. 7.1 By the 1800s new views about species and the history of Earth had emerged
Jean Batiste de Lamarck, a French biologist was one of the first to suggest that species change over time (evolution).
Charles Lyell, an English geologist and friend of Charles Darwin suggested that an old Earth had gradually changed through slow, accumulating processes.
Figure 7.1-1d Darwin’s Cultural and Scientific Context–4 of 15
Figure 7.1-1f Darwin’s Cultural and Scientific Context–6 of 15

7. 7.1 Darwin’s influences and experiences led him to his theory of evolution
As a youth, Darwin spent time observing nature.
He first studied beatles
After graduated from college, he travels around the world on the HMS Beagle ( )
Darwin's travels allowed him to compare species from different regions.
Figure 7.1-1g Darwin’s Cultural and Scientific Context–7 of 15
Figure 7.1-1l Darwin’s Cultural and Scientific Context–12 of 15
The voyage of the Beagle: 1831–1836

8. 7.1 Darwin began an in-depth study of change over time (evolution)
Darwin spent decades reading, analyzing his specimens, and discussing ideas with colleagues.
Darwin was the first to propose a mechanism to explain how species could evolve: natural selection.
Figure 7.1-1i Darwin’s Cultural and Scientific Context–9 of 15
Darwin’s beetle collection

9. 7.2 Opening Questions: Observations on the natural world: True or false?
If the answer is false, explain why:
True or false: Populations tend to be stable in size.
True or false: Resources are unlimited.
True or false: All individuals of a particular species in a population are exactly alike.
True or false: Traits can be inherited.

10. 7.2 In The Origin of Species Darwin made two important points
First, modern species have descended from common ancestors (evolution).
Second, natural selection is the mechanism of evolution.
Figure 7.1-1o Darwin’s Cultural and Scientific Context–15 of 15
Darwin arrived at the idea of evolution by natural selection through several important observations and conclusions.

11. Observation: Overproduction
7.2 Darwin first observed that populations produce more individuals than can survive
Observation: Overproduction
More individuals are born than can be supported by the environment.
Observation: Limited resources
The amount of resources (such as food, water, shelter, sunlight) stays relatively constant.
Figure 1.7-1b Natural Selection: Unequal Reproductive Success–2 of 6
Figure 1.7-1c Natural Selection: Unequal Reproductive Success–3 of 6

12. Conclusion: Competition
7.2 Darwin concluded that competition was a factor for all living things
Conclusion: Competition
More offspring are born than can be supported by limited resources; not all individuals survive and reproduce. (differential reproductive success)
Observation: Variation
Darwin also observed that no two individuals are alike.
Figure 1.7-1d Natural Selection: Unequal Reproductive Success–4 of 6
Figure 1.7-1e Natural Selection: Unequal Reproductive Success–5 of 6

13. Conclusion: Natural selection
7.2 Darwin concluded that favorable variations will be naturally selected
Conclusion: Natural selection
Those individuals with variations that make them best suited to their environment will, on average, be more likely to survive and reproduce.
Figure Evolution via Natural Selection in Action

14. 7.2 Darwin concluded that natural selection can lead to evolution
Observation: Heritability
The traits of an organism are likely to be passed to the next generation.
Conclusion: Evolution
Because traits are passed from one generation to the next, and because certain members are more likely to survive and reproduce, a population will change over time, becoming better suited to its environment.
Figure 7.2-1f The Argument for Natural Selection–6 of 7

15. 7.2 Important points about evolution
Individuals don’t evolve.
Natural selection acts on individuals, but only populations evolve.
Natural selection works with heritable traits.
Only genetically coded traits are subject to natural selection.
Evolution does not have a goal.
Evolution occurs in response to local environmental conditions, not future ones.
Figure 7.2-1g The Argument for Natural Selection–7 of 7

16. 7.3 Opening Questions: How are Darwin’s observations and conclusions connected?
Replicate the figure below on a full page in your notes. Identify Darwin’s observations and conclusions. Draw connections between the ideas. For each connecting line write an explanation.
Variation
Heritability
Overproduction
Limited resources
Competition
Natural selection
Evolution
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Students should be familiar with the observations and conclusions as presented in section 7.2.

17. 7.3 The fossil record provides important evidence for evolution
Fossils form when organisms die, fall into accumulating sediment, and are compressed into rock.
Figure The Fossil Record

18. 7.3 Fossils provide a glimpse into the past
Fossils can be dated using their geological position and/or through radiometric dating.
Figure 7.3-3a A Gallery of Fossils–1 of 6
Figure 7.3-3b A Gallery of Fossils–2 of 6
Figure 7.3-3d A Gallery of Fossils–4 of 6
Figure 7.3-3e A Gallery of Fossils–5 of 6
Figure 7.3-3f A Gallery of Fossils–6 of 6

19. 7.3 Carbon 14
Carbon 14 nitrogen 14 for specimens younger than 50,000 years
The half life of C14 is about 5600 years
So if a sample has 1/2 of the original sample, than the sample is 5600 years old
If only ¼ of the original sample is present, than 2 half-lives have passed so the sample is 11,200 years old
An approximations can be determined by this
age of fossil= ½ life x number of half life's passed
So if one multiply by 2 if ¼ of the sample is left, if 12.5 % is left than that would be 3 half life’s

20. Radiometric dating Is the most common method for dating fossils.
Has helped establish the geologic time scale.
Different isotopes have different ½ life's
For example C14 has a half- life of about 5600 years
Radiometric dating method relies on radioactive dating techniques.
All radioactive isotopes have a particular half-life.
Length of time it takes for half of the radioactive isotope to change into another stable elements
Compare radioactivity of a fossil to that of a modern sample of organic matter.
Radiometric dating involves measuring content of radioactive isotopes such as
Carbon 14 nitrogen 14 for specimens younger than 50,000 years
K40argon 40 for specimens that are million years old such as dinosaur bones
Rb87St87 for Paleozoic rocks
Decay of uranium can also be used. Its half life is

21. 7.3 How does the fossil record provide evidence of evolution?
The fossil record reveals an ordered appearance of life on Earth, from prokaryotes to today’s life forms.
Transitional forms provide evidence of change within lineages.
Figure Evidence for Evolution Within the Fossil Record
Fossil whales with rear legs are examples of transitional forms.

22. 7.4 Opening Questions: Can we predict evolution?
Write a short answer to the question below:
What characteristics must be present in a population and the environment in order for natural selection to occur in a population?
Variation in population
Inheritable characteristics which lead to reproductive success
Selection pressure
Time
Adaptation
VISTA

23. Biogeography is the study of the geographic distribution of species.
7.4 The geographic distribution of species provides much evidence of evolution
Biogeography is the study of the geographic distribution of species.
For example, the geographic isolation of Australia accounts for the dominance of marsupial mammals.
Figure 7.4-1a Biogeography–1 of 9
Figure 7.4-1e Biogeography–5 of 9
Figure 7.4-1g Biogeography–7 of 9

24. A. Wallace and Biogeography
7.4 The geographic distribution of species provides much evidence of evolution
A. Wallace and Biogeography
On the Tendency of Varieties to Depart Indefinitely From the Original Type
Alfred Wallace also came up with natural selection after his journey around the world as a mechanism by which populations evolve
He studied the affects of geography on the biological distribution and diversity - Biogeography
© 20## Pearson Education, Inc.

25. 7.4 Comparative anatomy provides much evidence of evolution
Comparisons of the body structures of modern organisms is called comparative anatomy.
Figure 7.4-2d Comparative Anatomy–4 of 4
Comparisons of the body structures of modern organisms, a discipline called comparative anatomy, can provide insight into evolutionary history.
Examination of animal forelimbs—here, a bat wing, a porpoise flipper, and a human arm—show that they are all constructed from similar bones.

26. 7.4 Comparative anatomy can provide insight into evolutionary history
Figure 7.4-2a Comparative Anatomy–1 of 4
Figure 7.4-2b Comparative Anatomy–2 of 4
Figure 7.4-2c Comparative Anatomy–3 of 4
Examination of animal forelimbs shows they are all constructed from similar bones.

27. 7.4 DNA and bioinformatics provide much evidence of evolution
All life uses DNA for genetic code.
Closely related species will have similar DNA and protein sequences.
Such as in primates
Bioinformatics employs computational tools to process genetic data.
Figure Bioinformatics

28. 7.5 Opening Questions: What exactly is a population?
Populations are the smallest unit that can evolve. But what is a population?
Answer the following questions:
1. How would you define a population?
Is your class a population?
Is your country a population?
Is the entire human species a population?
2. How might biologists define a population? Explain.
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Students should understand that population in biology is, in part, defined by scale.

29. 7.5 Populations are the units of evolution
Natural selection acts on individuals.
However, evolution is defined only in terms of changes in a population over time.
Figure b Ecology Can Be Studied on Many Levels–2 of 5
A population is a group of individuals of the same species living in the same place at the same time.

30. 7.5 Members of a population are capable of meeting and mating
Birds: Same population
Fish: Same population
Squirrels: Different population
Figure Populations
Squirrels don’t swim!

31. 7.5 The members of a population may carry different gene versions
The gene pool consists of all versions of all the genes carried by all the individuals in a population.
Genetic variation in a gene pool can arise through mutation.
Sexual reproduction ensures that genes are randomly mixed.
Figure Gene Pools

32. 7.5 Natural selection acts on the gene pool
Traits that enhance survival and reproduction will be represented with increasing frequency in the gene pool.
A generation-to-generation change in the gene pool is called microevolution, which is evolution occurring on its smallest scale.
Figure 1.7-1b Natural Selection: Unequal Reproductive Success–2 of 6

33. 7.5 Microevolution is a generation-to-generation change in the gene pool
Figure Microevolution
Taken over many generations, microevolution can result in the gradual adaptation of species to the local environment.

34. 7.6 Opening Questions: Can you breed a Chihuahua?
Imagine you have a pack of wolves.
How could you turn your wolves into Chihuahuas?
Explain why your strategy would work.
Figure b Ecology Can Be Studied on Many Levels–2 of 5
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Try to engage students and get them thinking about what traits besides size they might select for in a breeding trial. What happens to the individuals that don’t breed? What happens to their genes?
Background: Students can use their knowledge of natural and artificial selection to select for smaller and smaller individuals. One might be able to breed Chihuahuas from wolves by selectively choosing to mate small wolves with smaller wolves for many generations. Students should also focus on other desirable traits, such as good disposition, puppy-like behavior and appearance, tan fur, etc.
NOTE: Some students may not see the connections and make suggestions such as moving wolves to Mexico (climate) or training them to become less aggressive. Try to guide them to the importance of heritable traits.
Extra thought question: Is body size the only trait that matters?

35. Mutations: Random changes to DNA which can create new genes.
7.6 Changes to the genetic makeup of a population can arise via two mechanisms
Mutations: Random changes to DNA which can create new genes.
Sexual recombination: During the formation of sperm and eggs, chromosomes can exchange pieces of DNA, shuffling genes.
Figure 7.6-1a Genetic Variation–1 of 2
Figure 7.6-1b Genetic Variation–2 of 2
Crossing over

36. 7.6 Natural selection and fitness
Darwinian fitness is the contribution that an individual makes to the gene pool of the next generation in comparison to the contributions from other individuals.
The fittest individual is not always the strongest.
Figure Darwinian Fitness
There are many sorts of adaptations that can improve fitness.
Camouflage is an adaptive trait.

37. 7.6 Mechanisms of evolution
What can lead to changes in a gene pool over successive generations?
Hint: We’ve already discussed one important mechanism that can result in gene pool change.
Figure 1.7-1b Natural Selection: Unequal Reproductive Success–2 of 6
Active Learning: Mini question can be done as a short ASK-YOUR-NEIGHBOR activity.
Natural selection is the primary mechanism that can lead to a change in a gene pool, also known as evolution.

38. 7.6 Mechanisms of evolution
In addition to natural selection, there are other mechanisms that can also contribute to evolution in gene pools.
Genetic drift
Bottleneck and founder effect
Gene flow
Sexual selection
Figure f Primates Within the Tree of–10 of 17
In evolving populations, some combination of all the mechanisms operates.

39. Genetic drift is a change in a gene pool due to chance.
7.6 Genetic drift can lead to changes in a gene pool over successive generations
Genetic drift is a change in a gene pool due to chance.
For example, genes may be lost if a few individuals die or migrate at random.
This is important in small, or isolated, populations.
Figure 7.6-3a Mechanisms of Evolution–1 of 5

40. 7.6 The bottleneck and founder effects can change gene pools
If a population is drastically reduced in numbers, that is a bottleneck.
If a few individuals migrate to a new isolated habitat, that is a founder effect.
In either case, by chance, some genes will be lost from the gene pool.
Figure 7.6-3c Mechanisms of Evolution–3 of 5
In the 1800s, cheetah numbers were drastically reduced.

41. 7.6 Gene flow tends to reduce differences among gene pools
Most populations are not isolated.
Gene flow is the genetic exchange among populations due to migration.
Drifting pollen may transfer genes between distant populations, causing them to become more genetically similar over time.
Figure 7.6-3b Mechanisms of Evolution–2 of 5

42. Females may choose males for their traits.
7.6 Sexual selection can lead to changes in a gene pool over successive generations
Sexual selection is a form of natural selection that depends on an individual’s ability to obtain a mate.
Females may choose males for their traits.
Males may compete with each other for access to mates.
Figure 7.6-3d Mechanisms of Evolution–4 of 5
Figure 7.6-3e Mechanisms of Evolution–5 of 5

43. 7.6 Review Questions: Survival of the prettiest?
While working on his theory of natural selection, Darwin was quite troubled about peacocks.
A long tail makes them vulnerable to predators.
Figure 7.9-2a Reproductive Barriers–1 of 6
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity.
Background: Answers will vary. Students should start to consider that natural selection and sexual selection may promote different characteristics.
Why might a peacock, with its long, beautiful tail, initially have troubled Darwin?

44. 7.7 Opening Questions: Do only the strong survive?
Do you agree or disagree with the following statement? Explain your answer.
Only the strongest individuals in a population will survive to reproduce.
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Many students may have misconceptions regarding “survival of the fittest” and what that means for natural selection. This question is a good one for launching a deeper discussion on the meaning of biological fitness.

45. Macroevolution is genetic change on a large scale.
7.7 Macroevolution encompasses the major changes in the history of life
Macroevolution is genetic change on a large scale.
Speciation is the evolutionary formation of new species.
Figure 1.7-3b The Diversity and Unity of Life–2 of 5
Earth’s incredible diversity represents a long history of evolution, as ancestral species gave rise to one or more new species.

46. 7.7 Speciation may occur through two different mechanisms
In nonbranching evolution, an ancestral population changes gradually.
In branching evolution, an ancestral population splits into two or more populations.
Figure 7.7-1a Speciation–1 of 2
Figure 7.7-1b Speciation–2 of 2

47. 7.7 Novel features may spur large-scale evolution
Throughout the history of life on Earth, novel features have evolved.
The evolution of feathers and flight in birds is an example of how structures that serve one role can gradually change to serve another.
Figure Novel Features
Throughout the history of life on Earth, novel features have evolved. Ancient birds evolved from flightless reptiles, humans evolved bipedalism (an upright, two-legged posture), and flowering plants evolved from nonflowering predecessors. How does such large-scale innovation occur? The fossil record shows that structures that serve one role can gradually change to serve another. New features may arise gradually; each species is adapted for its environment, but the lineage of species shows the evolution of a new structure. For example, birds evolved from one lineage of dinosaurs. These dinosaur ancestors had a very lightweight skeleton that may have helped them be agile and elude predators. Over time, this lineage evolved the ability to take long hops, then short glides, and eventually full-fledged flight. While each species was adapted for its own environment, viewed over a long time, the evolution of flight is a good example of a large-scale macroevolutionary change.

48. 7.7 Rapid species diversification follows mass extinctions
There have been five mass extinctions in the history of life.
Following the mass extinction of the dinosaurs 65 mya, mammals diversified.
Figure 7.7-3d Mass Extinctions–4 of 4

49. 7.8 Opening Questions: Can you trust Fred Flintstone?
Did any of our human ancestors ever ride a dinosaur to work?
Did they ever fry up a dinosaur egg for breakfast?
Or have a cute little “dino” for a pet?
Figure Novel Features
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Many students may have misconceptions about the history of life on Earth.
As fun as it is to imagine, what is wrong with the above scenarios? Explain.

50. Each era represents a distinct period in the history of life.
7.8 The geological record ties together the history of Earth and its life
Geologists recognize four broad eras in the history of Earth, each marked by the appearance of distinctive life.
Each era represents a distinct period in the history of life.
Figure 7.8-1b The Geologic Record–2 of 7
Precambrian
Paleozoic
Mesozoic
Cenozoic

51. 7.8 Precambrian era: 4.6 bya to 541 mya
Highlights from the Precambrian:
4.6 bya: Earth forms
3.5 bya: Oldest known prokaryote (primitive-celled) fossils
2.1 bya: Oldest known eukaryote (modern-celled) fossils
Figure 7.8-1c The Geologic Record–3 of 7
Figure 7.8-1d The Geologic Record–4 of 7
Figure 7.8-1e The Geologic Record–5 of 7

52. 7.8 Paleozoic era: 541 to 251 mya Highlights from the Paleozoic:
541 mya: Explosion in animal diversity within the oceans
420 mya: Plant life begins on land
370 mya: Animals migrate to land
251 mya: Mass extinction event
Figure 7.8-1f The Geologic Record–6 of 7
Figure 7.8-1g The Geologic Record–7 of 7

53. Highlights from the Mesozoic: 230 mya: First dinosaurs
7.8 Mesozoic era: 251 to 65 mya
Highlights from the Mesozoic:
230 mya: First dinosaurs
100 mya: Flowering plants begin to dominate the land
Figure 7.8-2d Plate Tectonics–4 of 8
Figure 9.6-1n Major Events in the Evolution of Plants–14 of 15

54. 7.8 Cenozoic era: 65 mya to today
Highlights from the Cenozoic:
65 mya: Extinction of dinosaurs and diversification of mammals
200,000 years ago: Appearance of anatomically modern humans
Figure 7.8-2e Plate Tectonics–5 of 8
Figure 7.8-2g Plate Tectonics–7 of 8

55. 7.8 Earth’s geology has had a profound impact on the history of life
The Earth’s crust is composed of large tectonic plates floating atop a very hot layer of rock called the mantle.
Plate movement continuously rearranges the geography of the continents.
Figure 7.8-2b Plate Tectonics–2 of 8

56. 7.8 The Earth is a dynamic planet
Geological upheavals can be catastrophic in the short term and can alter the evolution of life on Earth in the long term.
Earthquakes, mountain building, volcanoes
Changes in the Earth’s geology over time have intertwined with the history of life on Earth.
Figure 7.8-2a Plate Tectonics–1 of 8

57. 7.9 Opening Questions: Lions and tigers! Oh, my!
Imagine you are visiting the zoo, and in the Big Cats exhibit you see lions from Africa and tigers from Asia.
We consider lions and tigers different species. Why?
In captivity, mating between lions and tigers may lead to hybrid “ligers.” Are “ligers” a species? Why or why not?
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Answers will vary. Students generally struggle with the concept of species without realizing that biologists also wrestle with the idea and that there is no clear definition of a species. A “liger” is a hybrid from a cross between a male lion (Panthera leo) and a female tiger (Panthera tigris). Most students are familiar with “ligers” from popular films, but a short video may be fun.

58. The word “species” is derived from a Latin word meaning “appearance.”
7.9 What is a species?
The word “species” is derived from a Latin word meaning “appearance.”
However, appearance alone cannot be used to tell one species from another.
Figure 7.9-1a What Is a Species?–1 of 7
Figure 7.9-1d What Is a Species?–4 of 7

59. What types of species might not fit the definition above?
7.9 What is a species?
The most commonly used definition of species is a population that is capable of interbreeding to produce healthy, fertile offspring.
Figure 7.6-3a Mechanisms of Evolution–1 of 5
Active Learning: Mini question can be done as a short ASK-YOUR-NEIGHBOR activity.
What types of species might not fit the definition above?

60. 7.9 What is a species?
Our earlier definition focused on interbreeding doesn’t work for all species.
Bacteria reproduce asexually.
For extinct organisms, we can’t know if they were capable of mating.
For some organisms, we have to use appearance, or another means, to determine species groups.
Figure 7.9-1f What Is a Species?–6 of 7
Figure 7.9-1g What Is a Species?–7 of 7

61. 7.9 Reproductive barriers maintain species
For species that we can define as a group of individuals capable of successfully interbreeding, what keeps them separate?
One or more reproductive barriers prevent members of different species from breeding.
Figure 7.9-1b What Is a Species?–2 of 7
Figure 7.9-1c What Is a Species?–3 of 7
Active Learning: Mini question can be done as a short ASK-YOUR-NEIGHBOR activity.
What might prevent Eastern and Western meadowlarks from interbreeding?

62. 7.9 Reproductive barriers maintain species
Behavioral isolation: Members of a species often identify each other through specific rituals.
Mating time differences: Many species are able to reproduce only at specific times.
Habitat isolation: If species live in slightly different habitats, they may never meet.
Figure 7.9-2a Reproductive Barriers–1 of 6
Figure 7.9-2b Reproductive Barriers–2 of 6
Figure 7.9-2c Reproductive Barriers–3 of 6

63. 7.9 Reproductive barriers maintain species
Mechanical incompatibility: Members of different species often cannot mate because their anatomies are incompatible.
Gametic incompatibility: The gametes (sperm and egg of different species usually cannot fertilize each other.
Hybrid weakness: Offspring of two species may be unfit, or they may be sterile.
Figure 7.9-2d Reproductive Barriers–4 of 6
Figure 7.9-2e Reproductive Barriers–5 of 6
Figure 7.9-2f Reproductive Barriers–6 of 6

64. 7.9 Review Questions: Lions and tigers! Oh, my!
Lions and tigers can produce a hybrid
“liger” offspring.
Does this mean that lions and tigers are the same species? Explain.
Active Learning: Mini question can be done as a short ASK-YOUR-NEIGHBOR activity.
Background: Answers will vary. Students generally struggle with the concept of species without realizing that biologists also wrestle with the idea and that there is no clear definition of a species. A “liger” is a hybrid from a cross between a male lion (Panthera leo) and a female tiger (Panthera tigris).  Most students are familiar with “ligers” from popular films, but a short video may be fun.
Students should eventually focus on normal habitat isolation among lions and tigers.

65. 7.10 Opening Questions: How do we get new species?
Imagine that a small flock of forest birds gets blown off course during a hurricane. The flock lands on a small, dry, and grassy island. You locate this population 300,000 years later.
Do the current birds look the same or different from the original colonists? Draw pictures of your imagined birds.
Do they have the same behaviors?
Would you consider them the same species or different from the original species? Explain.
Figure Food Webs
Active Learning: Opening questions can be done as a 1-minute THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. Encourage students to use their drawing skills to illustrate their answers.
Background: Answers will vary.

66. 7.10 How do we get new species?
Speciation occurs when one ancestral species evolves into one or more new species.
Some event separates a population:
Time, space, or genetics
Populations then diverge along their own evolutionary path.
Original Population
Species A
Species B
Speciation can occur through various mechanisms.

67. 7.10 New species may form over long periods of time
In the graduated model, a species acquires small adaptations to its environment over millions of years.
Figure Graduated Model

68. 7.10 New species may form relatively rapidly
In the punctuated equilibrium model, there are periods of stasis interrupted by occasional bursts of speciation.
530 million years ago during a period called the Cambrian explosion, the rate of evolution was an order of magnitude higher than the normal rate. (It still required millions of years.)
Figure Punctuated Equilibrium

69. 7.10 New species may form after geographic isolation
Allopatric speciation may occur when a physical barrier isolates populations.
The formation of the Grand Canyon produced two isolated habitats. One species of squirrel is now found exclusively on each side of the canyon.
Figure c Allopatric Speciation–3 of 3

70. 7.10 New species may form within a parent species
Sympatric speciation may occur quite suddenly due to large-scale genetic changes. (There is no physical barrier.)
Figure Sympatric Speciation

71. 7.11 Opening Questions: What do we know about evolution anyway?
Write a short response to the following question:
What are at least three things you know that provide supporting evidence for evolution?
Active Learning: Opening questions can be done as a 1-minute WRITE-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.

72. 7.11 Taxonomy is the classification of life
Taxonomy is the identification, naming, and classification of species.
All life is classified into one of three large groups called domains based on cell type.
Figure 1.6-1a The Domains of Life–1 of 3

73. 7.11 Where does a tiger fit in the taxonomic hierarchy?
Starting with a domain, every organism can be placed into the taxonomic hierarchy, an ordered series of progressively smaller categories.
The hierarchy ends with the species name.
Panthera tigris
Figure i Taxonomy–9 of 9

74. 7.11 Where does a tiger fit in the taxonomic hierarchy?
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Figure a Taxonomy–1 of 9

75. 7.11 Where does a tiger fit in the taxonomic hierarchy?
Species are identified using the last two groups in the hierarchy: Genus species.
This binomial (two-part) is sometimes called a “scientific name.”
Panthera tigris
Figure b The Three-Domain System–2 of 2

76. 7.12 Opening Questions: How can we map our ancestry?
Sketch out a quick family lineage for your immediate family.
How far back can you go? Your grandparents? Great-grandparents? Great-great-grandparents?
We often refer to our “family tree” when discussing our ancestry.
What shape best describes your family sketch? Explain.
Active Learning: Opening questions can be done as a staggered THINK-PAIR-SHARE activity. The opening questions are designed as a set of engagement questions to get students thinking. The questions may also be adapted for the use of survey technology such as clickers.
Background: Tree-like relationships are common in human ancestry. Students should apply the same spatial conceptual thinking to evolutionary trees.
Why might trees be a useful term to represent relationships?

77. 7.12 Evolutionary relationships may be represented by branching trees
Phylogenetic trees are one way to reflect the evolutionary history of organisms.
Phylogenetic trees present a hypothesis about the evolutionary history of related species.
Species A
Species B
Species C

78. EVOLUTION: BIOLOGY’S UNIFYING THEME
Life evolves.
Each species is one twig of a branching tree of life extending back in time through ancestral species more and more remote.
Species that are very similar, such as the brown bear and polar bear, share a more recent common ancestor.
Reading the table:
10 million years ago how many species of bear existed (answer: 2)
Presently how many species of bear exist?
Answer: 8
Of the bears that exist today which two are most closely related?
phylogeny n : the sequence of events involved in the evolutionary development of a species or taxonomic group of organisms
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79. 7.12 Bear © 20## Pearson Education, Inc.
The Polar bear and the Brown bear are closely related
They share so many genes they are able to form hybrids
Which two bears species are most closely related after these two?
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80. The analysis of clades is called cladistics.
7.12 Clades can be thought of representing a branch on the tree of life
A clade is a any group of species that consists of an ancestral species and all its descendants.
The analysis of clades is called cladistics.
Figure Cladistics

81. 7.12 Reading phylogenetic trees can provide insights into the interrelationships of life
Species A
Species B
Species C
The tips of the tree represent groups of the most recently evolved species.
To determine how closely related two species are, find their most recent common ancestor.