GRADE LEVEL: 5-8

TOPIC/SUBJECT MATTER: Life Science

TIME ALLOTMENT: Two 45-minute class periods

OVERVIEW:

During this video-enhanced lesson, students will learn that all dogs came from one ancestor- the wolf. Students will watch and discuss video segments from the NATURE film “Dogs that Changed the World,” and explore different theories about how this transformation happened. Students will learn about different breeds of dogs and create a book with pictures and information about a variety of dog breeds. In the culminating activity, students will interview a dog owner and create a poster and/or a presentation about his/her dog.

MEDIA RESOURCES

Video

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Clip 1: From Wolf to Dog

Reflections about the transformation from wolf to dog

Clip 2: The Speed of Change

Exploring the speed of evolution

Clip 3: Today’s Dog

A quick look at the dogs of today

Websites

American Kennel Club

This Web site includes information about the internationally-recognized breeds.

National Geographic Web sites’ Animal Section
This Web site features many photos of animals including photos of dogs and wolves, which can be used in this lesson.

Standards:

National Science Education Standards, Grades 5-8

LIFE SCIENCE: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of

• Regulation and behavior

o       An organism’s behavior evolves through adaptation to its environment. How a species moves, obtains food, reproduces, and responds to danger are based in the species’ evolutionary history.

• Diversity and adaptations of organisms

o       Millions of species of animals, plants, and microorganisms are alive today. Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry.

o       Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.

MATERIALS

For each student:

• “Dog Breed” Student Organizer (PDF) (RTF)
• “Dog Interview” Student Organizer (PDF) (RTF)

For the class:

• Photographs of a few very different looking dogs, such as a Chihuahua, a Saint Bernard and a Greyhound. (A good source for these photos is the American Kennel Club Web site.)
• Two photographs of a wolf (full-body and close-up of head)

OBJECTIVES

Students will be able to:

• Explain that all dogs evolved from wolves;
• Discuss theories about how the wolf evolved into the dog;
• Explain how quickly the transformation from wolf to dog might have happened;
• Understand how breeding animals for specific traits can result in the altered look and behavior of the descendents of those animals;
• Describe different breeds of dogs;
• Discuss the behaviors, skills, appearance and personality of one particular dog and explain whether the dog “fits in” with the general description of the breed.

Prep for Teachers

Prior to teaching this lesson, you will need to:

Preview all of the video segments and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Print out a copy of the “Dog Breed” and “Dog Interview” Student Organizers for each student.

Print out photographs of a few (3-4) very different looking dogs, such as a Chihuahua, a Saint Bernard and a Greyhound. (A good source for these photos is the American Kennel Club Web site.)

Print out two photos of a wolf – a full body shot and a close-up of its head. (One good place to look for wolf photos is the Animal Section of the National Geographic Web site.)

Proceed to Activities

Excerpts from the NATURE episode, “From Wolf to Dog”

Downloadable QuickTime versions of the video segments:
(Note: To download a video, right click on the video title and click “Save Link As…’ or “Save Target As…”. On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)
Clip 1: From Wolf to Dog

Clip 2: The Speed of Change

Clip 3: Today\’s Dog

The olm, a troglobite

To see life on another planet, most would suggest a radio telescope or a NASA explorer vehicle. Yet immediately below the earth’s surface there exists an otherworldly ecosystem populated by creatures that never see the light of day. These animals are the troglobites — crustaceans, amphibians, insects and more — built to survive in the dark, limestone labyrinths that form most of the world’s cave systems.

A pseudoscorpion that doesn’t have a stinging tail and instead injects venom with its claws. A Nelson cave spider with claws on two of its super-long legs that measure just shy of six inches. A whitish, almost transparent cave crayfish that can live over 150 years. These are just some of the troglobites, many of which possess similar evolutionary adaptations: blindness, long limbs and spiky feet to better navigate rocky terrain, and lack of pigmentation as there is no need for camouflage in the dark.

Of all the troglobites, it is perhaps the proteus anguinus, or the olm, that is the star. In Slovenia, a tourism industry exists for those who desire a glimpse of the ghostly salamander that’s beguiled humans for hundreds of years. The first written account of the olm dates back to 1689, in which scholar Janez Vajkard Valvasor disputed the belief that olms were baby dragons. Found in the Dinaric Karst of Europe, it’s easy to see why olms could be fodder for myth. They are blind, yet have barely visible, regressed eyes covered by skin. Their serpentine body can grow over a foot in length, and is covered by whitish, translucent skin that’s artfully highlighted by two frilly pink gills at the back of its head. And, unlike other amphibians that metamorphose into an adult form, the olm retains its larval features, a phenomenon known as neotony. Olms spend their whole lives in water, and so there is no need for them to develop terrestrial characteristics.

In keeping with this fairytale-like appearance, olms are said to be able to live up to 100 years and can go without eating for several. Yes, several years. They, like many troglobites, have exceptionally slow metabolism in large part because of the dearth, or erratic availability, of food. Like other troglobites, the olm compensates for lack of vision by using other, specialized senses. Olms’ ears are capable of receiving sound waves in water and vibrations from the ground, their sense of smell is keener than that of most amphibians, and they possess sensors in their heads called “ampullary organs” that enable them to detect weak electric fields.

Despite such specialized capabilities, troglobites are critically connected to what’s going on above earth’s surface. For a nutritious banquet, some troglobites feast on piles of bat guano found on cave grounds. Tree roots that grow through cracks in a cave’s ceiling and leaves that flow in with water can also provide nutrition. But this water can also bring destruction. Human waste — such as sewer leaks, runoffs, and pesticides — can flow into caves disrupting an ecosystem so sensitive it is said that even human dandruff can upset its balance.

Excavations and the building of roads can also threaten cave life directly. It’s important to note that most of the world’s caves have yet to be fully explored or discovered. The limestone labyrinths beneath us are indeed the earth’s last frontier. It’s a fascinating notion –- some of us may be living above an ecosystem populated by strange species, some millions of years old, and not even know it. In 2007, environmental protection officials in Australia halted a multi-billion dollar iron ore mining proposal when 11 species of troglobite were discovered in the area to be mined. Unfortunately, the ruling was overruled several months later. The battle between moneyed interests and our wildlife continues, unfortunately with greater frequency and scope.

Troglobites are at great risk. This includes the beloved olm which is presently listed by the IUCN as threatened, a circumstance that should be taken very seriously, not only because we should be stewards of our planet (above its surface and below) or because the olm is a fascinating, wonderful species, but also because it is the olm’s very sensitivity to such things as pollution that portends what affects humans as well.

Photo © WNET.ORG/Icon Films

It soars the skies with an effortless elegance. It can catch falling prey mid-flight and even dive-bomb into rivers to snag wriggling salmon. There is no question about it: the American bald eagle is a highly specialized predator. But what is the evolutionary background that allows the bald eagle to pull off these amazing maneuvers?

It may be difficult to believe, but the ancestors of bald eagles have lived on Earth for eons. Evolutionary biologists believe that birds evolved from reptiles. From their skeletal structure to their blood cells, today’s birds share a surprising evolutionary foundation with reptiles. According to biologists, feathers may have evolved from the scales of reptilian skin.

Between 144 million and 66 million years ago, during the Mesozoic era, the first birds began to evolve. Fossil records from this period reveal that the earliest birds had teeth. Eventually, tens of millions of years ago, an ancient group of birds called kites developed. Like today’s bald eagle, early kites are thought to have scavenged and hunted fish.

Finally, about 36 million years ago, the first eagles descended from kites. First to appear were the early sea eagles, which — like kites — continued to prey on fish and whose feet were free of feathers, along with booted eagles, which had feathers below the knee. While no one knows precisely when the bald eagle appeared on the scene, the earliest known fossil remains that closely resemble the bald eagle date back to about a million years ago.

Like the kites, bald eagles have featherless feet, but they also developed a range of other impressive adaptations that help them hunt fish and fowl in a watery environment. Each foot has four powerful toes with sharp talons. Tiny projections on the bottom of their feet called “spicules” help bald eagles grasp their prey. Ospreys, which are also believed to be descendents of kites, have similar projections on their feet. Could these spicules be a remnant of the birds’ shared reptilian ancestry? A bald eagle also has serrations on the roof of its mouth that help it hold slippery fish, and incredibly, the black pigment in its wing feathers has been found to strengthen the feathers against breakage when diving into water.

Obviously, there is much more than their striking white heads that sets these iconic raptors apart from the crowd. Their incredible physiology, built for life near the water, is literally millions of years in the making.

Photo © Laura Johnson

GRADE LEVEL: Grades 9-10

TIME ALLOTMENT: Two to three 45-minute class periods

OVERVIEW: The structure of an organism is related to its function and the role it plays in its environment. Many structural differences can be found within a species. These structural differences are often adaptations that allow organisms to better survive in their particular environment. These evolutionary adaptations develop through the process of natural selection.

This lesson explores different adaptations and variations in birds, using the NATURE episode “Extraordinary Birds.” It focuses on bird beaks, migratory patterns, and birds’ ability to co-exist with humans. Students will define key concepts from the lesson, discuss and explore different adaptations of birds, and analyze relationships between the concepts learned. This lesson can be taught independently, or it can be used as a precursor to the New York State Core Curriculum “Beaks of Finches” lab. Students must have a basic knowledge of evolution and natural selection in order to successfully complete this lesson.

SUBJECT MATTER: Biology/ Living Environment

LEARNING OBJECTIVES:

Students will be able to:

• Discuss and define key concepts from the lesson, including adaptation, migration, and interaction between humans and birds;
• Describe how particular characteristics of bird beaks reflect birds’ adaptations to their particular environments;
• Explain how different environmental factors can affect the migration cycle of the Rufous Hummingbird;
• Demonstrate understanding of how adaptations in different species of birds assist their interactions with humans;
• Create a concept map using different adaptive traits of birds.

STANDARDS AND CURRICULUM ALIGNMENT:

National Science Education Standards:

CONTENT STANDARD A: Science Inquiry
As a result of activities in grades 9-12 students should develop abilities necessary to do scientific inquiry and understand about scientific inquiry. To develop scientific inquiry skills students must actively participate in scientific investigations and they must actually use the cognitive and manipulative skills associated with the formulation of scientific explanations.

CONTENT STANDARD C: Life Science
As a result of activities in grades 9-12 students should develop understandings of:

• Biological Evolution
• Interdependence of organisms
• Behavior of Organisms

Students’ understanding of biology will expand by incorporating more abstract knowledge, such as the theories of evolution.

NEW YORK STATE CORE CURRICULUM ALIGNMENTS

Living Environment Core Curriculum:

STANDARD 1: Students will use mathematical analysis, scientific inquiry, and engineering designs, as appropriate, to pose questions, seek answers, and develop solutions.

Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing and creative process.

Performance Indicator 1.2: Hone ideas through reasoning, library research, and discussion with others, including experts.

1.2a. Inquiry involves asking questions and locating, interpreting, and processing information from a variety of sources.

Key Idea 3: The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into natural phenomena.

Performance Indicator 3.1: Use various methods of representing and organizing observations (e.g., diagrams, tables, charts, graphs, equations, matrices) and insightfully interpret the organized data.

3.1a Interpretation of data leads to development of additional hypotheses, the formulation of generalizations, or explanations of natural phenomena.

STANDARD 4: Students will understand and apply scientific principles and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

Key Idea 1: Living things are both similar to and different from each other and from nonliving things.

Key Idea 2: Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.

Key Idea 3: Individual organisms and species change over time.

Performance Indicator 3.1: Explain the mechanisms and patterns of evolution.

3.1g: Some characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.

3.1h: The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.

3.1i: Behaviors have evolved through natural selection. The broad patterns of behavior exhibited by organisms are those that have resulted in greater reproductive success.

Key Idea 6: Plants and animals depend on each other and their physical environment

Performance Indicator 6.1: Explain factors that limit the growth of individual populations

6.1g: Relationships between organisms may be negative, neutral, or positive. Some organisms may interact with one another in several ways. They may be in a producer/consumer, predator/prey, or parasite/host relationship or one organism may cause disease in, scavenge, or decompose another.

MEDIA COMPONENTS

Video

NATURE, Extraordinary Birds, selected segments:

Clip 1, “A Variety of Hummingbirds.”

Describes different traits and adaptations in various species of hummingbirds.

Clip 2, “Little Brain, Big Journey.”

Shows the migratory patterns and habits of the Rufous hummingbird.

Clip 3, “The Pigeon Express.”

Profiles a small business in which homing pigeons play a central role.

Clip 4, “Birds of Kundha Kulam.”

Demonstrates birds’ extraordinary impact on the agriculture of a small Indian community.

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Bird Adaptations – Beaks
An interactive Web site featuring the beaks of nine different species of birds, with descriptions of their characteristics and what they are best adapted for. It also includes a similar page for adaptations of birds’ feet, and worksheets to assess student comprehension.

MATERIALS

For each student:

• Rufous Hummingbird Student Organizer (PDF) (RTF)
• Beak Characteristics Student Organizer (PDF) (RTF)
• Vocabulary Student Organizer (PDF) (RTF)
• Practice Regents Questions (PDF) (RTF)

For each pair or group of students:

• For the Gallery Walk Activity: one pen or marker (a different color for each group)
• For the Concept Map Activity: two flip chart pages or large sheets of paper, one pad of sticky notes, one pen or marker
• Computer with internet access

For the class:

• Computer with internet access, projector and screen
• For the Gallery Walk Activity: flip chart pages with the following vocabulary terms written at the top of the page (one word per page): variation, natural selection, adaptation, competition, environment
• Teacher Answer Key (PDF) (RTF)
• Sample Concept Map (PDF)
• Scenarios for Vocabulary Terms – 2 copies (PDF) (RTF)
• Hat or bag (to hold Vocabulary Term scenarios)
• Regents Questions Answer Key (PDF) (RTF)

PREP FOR TEACHERS

Prior to teaching this lesson, you will need to:

Preview all of the video clips and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Prepare all classroom materials. Print out and make copies of the student organizers and answer keys. Prepare for the Gallery Walk activity by writing the following vocabulary terms at the top of flip chart pages or large pieces of paper (one term per page): Variation, Natural Selection, Adaptation, Competition, and Environment. Post the flip chart pages around the room. If you are not familiar with conducting a “Gallery Walk” in your classroom, review the procedure at the “How to Use Gallery Walk?” Web page.

For the Culminating Activity: Print two copies of the Scenarios for Vocabulary Terms sheet. Keep one sheet for teacher reference, and cut up the other sheet so that each scenario is on a separate slip of paper. Do not include the right-hand column (Vocab Key Code) on the cut-up slips. Put all the slips of paper into a hat or bag and mix well.

Next: Proceed to Activities

Background:
Cattle originally evolved over millions of years through a process of natural selection-also known as “survival of the fittest”-which made them adaptable to a wide variety of environments, including most of those inhabited by another highly adaptable species: humans. Once humans discovered how to domesticate cattle about 4,000 years ago, they began to selectively, or “artificially,” breed them for specific desired traits like meat and milk production. This resulted in animals fit less for survival in the wild than the satisfaction of human needs, but in purely genetic terms, the arrangement has proven highly successful for cattle. Cattle now thrive throughout the world in over 800 different breeds, each more or less successfully adapted to their environment and the needs of their human caretakers.

The excerpted clips from the NATURE episode “Holy Cow!” illustrate some of the naturally evolved and artificially selected attributes of cattle.

Suggested Focus Questions:

Clip 1: A Cow’s Digestive System

1. What role do microbes serve in a cow’s rumen?
2. Does this clip illustrate naturally or artificially selected attributes?
3. Why would a cow’s ability to eat grass make it ideal for human domestication?

Clip 2: Desirable Breeding Traits in Cattle

1. How many different breeds of cattle have humans created?
2. Would the qualities that make good beef cattle help them survive in the wild?
3. Besides milk and meat production, what other traits might humans wish to breed in cattle?

Clip 3: Different Breeds of Cattle

1. What might indicate that a cattle breed is adapted to cold climates like Scotland?
2. What do the different breed names refer to?
3. Why might “adaptability” be a desirable trait in a specific breed?

Downloadable QuickTime versions of the video segments:
(Note: To downoad a video, right-click on the video title and click “Save Link As…” or “Save Target As…” On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)

Clip 1, “A Cow’s Digestive System”

Clip 2, “Desirable Breeding Traits in Cattle”

Clip 3, “Different Breeds of Cattle”

GRADE LEVEL: Grades 9-12

TIME ALLOTMENT: Two to three 45-minute class periods

OVERVIEW: Cattle evolved through the slow process of natural selection until human domestication, which rapidly accelerated their development as an artificially selected species fit less for survival than to satisfy human needs. This lesson focuses on how and why humans have been so successful in selectively breeding cattle to suit these needs, while also exploring the limitations and consequences of this success.

Natural selection describes the process by which organisms best adapted to their environments are the ones that survive and reproduce. The Introductory Activity helps students understand that some traits, such as the ability to digest grass, made certain species more desirable for domestication by humans. The Learning Activities explore how, by nurturing and protecting animals that might not have survived in the wild, human domestication interrupted the process of natural selection. Reproductive success was no longer primarily determined by an animal’s most naturally adaptive survival traits, but rather by its artificially selected traits desirable to humans (primarily milk and meat production). The culminating activity presents a case study in which students consider the consequences of losing the naturally selected attributes of breeds less adapted to domestication.

Students should already be familiar with the concepts of evolutionary adaptation, natural selection, and DNA/genetic engineering.

SUBJECT MATTER: Biology/ Living Environment

LEARNING OBJECTIVES:

Students will be able to:

• Describe the traits of cows that make them suitable for domestication.
• Explain how the cow’s digestive system has adapted to its environment.
• Compare and contrast natural and artificial selection.
• Describe various breeds of selectively bred cattle and their desirable traits.
• Discuss some limitations and negative consequences of selective breeding.

STANDARDS AND CURRICULUM ALIGNMENT:

From the National Science Standards for Science Content, Grades 9-12.

CONTENT STANDARDS C: Life Science
As a result of activities in grades 9-12 students should develop understandings of:

Biological Evolution

• Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
• The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
• Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms.

Behavior of Organisms

• Like other aspects of an organism’s biology, behaviors have evolved through natural selection. Behaviors often have an adaptive logic when viewed in terms of evolutionary principles.

New York State Core Curriculum Alignments
From the Living Environment Core Curriculum.

STANDARD 4: Students will understand and apply scientific principles and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

Key Idea 2: Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.

Performance Indicator 2.2: Explain how technology of genetic engineering allows for human to alter genetic makeup of organisms.

2.2a: For thousands of years new varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits.

2.2b: In recent years new varieties of farm plant and animals have been engineered by manipulating their genetic instructions to produce new characteristics.

Key Idea 3: Individuals and species change over time.

Performance Indictor 3.1: Explain the mechanisms and patterns of evolution.

3.1e: Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life-forms as well as for the molecular and structural similarities observed among the diverse species of living organisms.

3.1f: Species evolve over time. Evolution is the consequence of the Interaction of (1) the potential for a species to increase its numbers… (4) the ensuring selection by the environment of those better able to survive…

3.1j: Behaviors have evolved through natural selection. The broad patterns of behaviors exhibited by organisms are those that have resulted in greater reproductive success.

3.1k: Evolution does not necessitate a long-term progress in some set direction. Evolutionary changes appear to be like the growth of a bush: Some branches survive from the beginning with little or no change, many die out altogether, and others branch repeatedly, sometimes giving rise to more complex organisms.

MEDIA COMPONENTS

Video

NATURE, Holy Cow, selected segments:

Clip 1, “A Cow’s Digestive System”

Clip 2, “Desirable Breeding Traits in Cattle”

Clip 3, “Different Breeds of Cattle”

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Breeds of Livestock
An Oklahoma State University Web site featuring photos and descriptions of various breeds of cattle from around the world.

World Climate Map
A map of the world showing different climate zones.

Genetic Engineering
A Regents’ preparatory Web site featuring a description of how the meaty English Shorthorn cow was selectively bred with the heat-resistant Brahman cow to produce the Santa Gertrudis, a hybrid which possesses the positive characteristics of both parent breeds.

Punnett Squares
An interactive Web-site which explains how Punnett squares can be used to determine the likelihood that certain traits will be passed on to future generations.

A Dying Breed
A New York Times article which discusses the pros and cons of increasing hybridization by Bahiman cattle ranchers in Uganda of their native Ankole cattle with Holstein cattle from the United States.

MATERIALS

For each student:

• “Traits of Ankole and Holstein Cattle” Student Organizer (PDF)(RTF)

For each group:

• “Man’s Best Friend?” Student Organizer (PDF)(RTF)
• “Cattle Breeding” Student Organizer (PDF)(RTF)
• “Finding the Balance” Student Organizer (PDF)(RTF)

For the class:

• “Traits of Ankole and Holstein Cattle” Student Organizer Answer Key (PDF)(RTF)
• “Man’s Best Friend?” Student Organizer Answer Key (PDF)(RTF)
• “Cattle Breeding” Student Organizer Answer Key (PDF)(RTF)
• “Finding the Balance” Student Organizer Answer Key (PDF)(RTF)
• Computer with Internet access, projector, and screen

PREP FOR TEACHERS

Prior to teaching this lesson, you will need to:

Preview all of the video clips and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Next: Proceed to Activities.

Background:
As hummingbirds and other bird species evolved over time, they developed a variety of traits and skills beneficial to both the birds themselves and to the continuation of their species. The vast array of hummingbird species is an example of the result of these evolutionary processes. Certain birds have developed beaks allowing them to feed at particular flowers, others have cultivated brightly colored plumage, and yet others are known for the exceptional skills at navigation. Many highly skilled bird behaviors are innate – certain bird species are born with these abilities, as is the case of the homing pigeon’s innate homing ability. Scientists often do not know how these skills have been acquired in the population, except to note that these traits became advantageous for the birds as their populations evolved in their respective environments.

The segments from the NATURE episode “Extraordinary Birds” show examples of the adaptations of different birds to their varying environments.

Suggested Focus Questions:

Clip 1: A Variety of Hummingbirds

1. Describe two types of hummingbirds with beaks adapted to specific flowers.
2. What makes hummingbird flight different from the flight of other birds?
3. Why do you think the different colors of hummingbirds present an advantage to the birds? Why might this trait have developed in hummingbirds?

Clip 2: Little Brain, Big Journey

1. How long is the Rufous hummingbird’s migration route?
2. Describe the path of the Rufous hummingbird’s migration.
3. How does the Rufous hummingbird vary its migratory path? How does it know to do so?

Clip 3: The Pigeon Express

1. What service do the pigeons provide for Rocky Mountain Adventures?
2. How were these pigeons trained for their jobs?
3. Based on the information in the clip, what do you think gives pigeons their innate homing ability?

Clip 4: Birds of Kundha Kulam

1. When do the flocks usually appear in Kundha Kulam?
2. What is associated with the birds’ appearance and the rainy season?
3. Are the birds actually “bringing the rain”? Why might the birds’ appearance in Kundha Kulam coincide with the rainy season?

Downloadable QuickTime versions of the video segments:
(Note: To download a video, right-click on the video title and click “Save Link As…” or “Save Target As…”. On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)

Clip 1, “A Variety of Hummingbirds”

Clip 2, “Little Brain, Big Journey”

Clip 3, “The Pigeon Express”

Clip 4, “Birds of Kundha Kulam”

The icon of the Arctic, the polar bear, is the ultimate survivor in one of the harshest areas on Earth. Reigning over a world of ice, tundra, and snow, this carnivore would seem to have a lineage that traces back to some mammoth creature of the icy regions.

But in fact, the polar bear’s closest ancestor is a land carnivore we associate more strongly with our forests. Over the years, scientists have uncovered an evolutionary path suggesting that polar bears are a relatively new species, and actually a subspecies, of Ursus arctos, more widely known as the brown bear. Scientific evidence has found that the brown bear, a species that also includes grizzly bears, was a “precursor” to polar bears, which then went on to develop specializations for inhabiting the harsh Arctic.

Proving their genetic compatibility, brown bears and polar bears can mate and produce viable, or fertile, offspring. It is this reproductive viability that establishes that an animal belongs within a given species. In 2006, a hybrid grizzly/polar bear, which some call a “pizzly,” was discovered in the Canadian Arctic, providing researchers proof that polar bears and grizzly bears can interbreed, even in the wild. And when researchers in Alaska compared the DNA of brown bears from around the world, looking for genetic links, they made an interesting discovery about one population of brown bears in particular. Analysis of the DNA of a distinct population of brown bears living on Alaska’s ABC islands, 900 miles south of the nearest polar bear, revealed that the ABC bears were even more closely related to polar bears genetically than they were to other brown bears.

So just when did polar bears arise as a separate subspecies? Genetic models show that the emergence of the polar bear could have taken place as recently as 70,000 years ago or as many as 1.5 million years ago. For many years, a fossil found at Kew Bridge in London was considered the oldest polar bear specimen. The fossil then placed the evolution around 70,000 years ago. But recently, scientists uncovered a fossilized jawbone from an island in the Arctic Ocean midway between Norway and the North Pole, dated to be at least 100,000 years old. Scientists believe this jawbone may represent the remains of the oldest-known polar bear, thus marking the appearance of the polar bear earlier than previously thought.

Relying on the fossil record and DNA analysis, scientists have been able to arrive at a clearer picture of the polar bear’s evolutionary path over the millennia. Some 200,000 years ago, when glaciers covered much of Eurasia, the Arctic Ocean was completely frozen. It was during this challenging period that brown bears began to wander in search of food. Approximately 125,000 years ago a population of brown bears in the far north of their range was likely split off from their brown bear ancestors, perhaps because of competition for food. The population likely became isolated by massive glaciers and, while most died in the harsh environment, those bears with an evolutionary advantage — ideal coat color and thickness for extreme cold — survived and bred. Over thousands of years, this population of bears underwent further evolutionary change, adapting even more specialized traits for surviving the harsh polar environment. When life in the North demanded teeth better shaped for ripping apart seals than munching berries, the polar bear’s molar teeth changed significantly from those of the brown bear. The bears also grew white fur, which camouflaged them in their snow-covered surroundings and gave them a hunting advantage. Scientists believe that at first these bears scavenged seal carcasses that had washed ashore, and gradually began to hunt the seals by waiting at the water’s edge as the seals surfaced to breathe. This is believed to be an important step in the evolution of a new subspecies of bear — Ursus maritimus or the polar bear.

Nature once exerted such extreme pressure on the brown bear that it eventually gave rise to a new, better-adapted subspecies, the polar bear. Now, once again, evolutionary forces are acting on this long-enduring species. As the Arctic warms, the polar bear’s unique specializations that once lent it an evolutionary edge, may now be the creature’s downfall. A changing climate may name a new king of the Arctic — the fierce and opportunistic brown bear.

Though the crocodile’s ancestry dates back 200 million years, the crocodile, as we know it today, first evolved about 80 million years ago. According to the fossil record, their body plan has changed little since, enabling them to outlive the dinosaurs and become the most advanced of all reptiles and the most successful freshwater predator.

There is no single secret to the crocodile’s success. With few natural predators, a permanent armor of bony plates covering most of its body and strong jaw muscles capable of crushing anything from bones to cast iron, the croc is an extremely tough and robust creature. A croc can survive even after serious injuries such as a torn off limbs or tail and has a powerful immune system that helps it survive for decades.

But its adaptations go beyond being hardy. One of the keys to its survival is something one might think of as primitive: cold-bloodedness. Like all reptiles, crocs are ectotherms, which means they must gather heat from their environment. Crocodiles have developed behaviors to control their body thermostat: they bask in the sun when cool and seek shade or water when hot. Ectotherms like crocs don’t need to eat regularly to warm their bodies, and so they save an enormous amount of energy that can be put to other use or stored for later. A croc’s metabolism is so evolved that its body uses and stores nearly the entirety of the food it consumes. This is one reason why larger crocodiles can go for over a year without eating a meal. In extreme situations, crocodiles appear to be able to shut down and live off their own tissue for a long period of time.

But most crocs eat much more often than that. In fact, the average croc eats about 50 full meals a year. When they feast, crocodiles are certainly not picky eaters. It’s said that a croc will feed on anything it can outswim or ambush and overpower. These reptiles have extraordinarily adaptable diets. Larger crocodiles will eat larger mammals and birds, but they’ll also eat fish and mollusks like snails. During difficult times, they will even scavenge for carrion. In fact, crocs will consume almost everything they encounter. And that means everything. A croc’s stomach is the most acidic of all vertebrates, allowing it to digest bones, horns, hooves, or shells. Nothing gets left behind in a crocodile’s dinner. In fact these hard objects are used as “gizzard stones” in the croc’s stomach to help grind coarse food.

While the crocodile’s diet may be undiscriminating, its social interactions are a bit more complicated. Crocs are more social than all other reptiles. Though they primarily lead solitary lives, they resort to group behavior for important activities such as hunting or raising hatchlings. Crocs don’t merely recognize one other, they form long-term relationships. They are hierarchical and communicate by means of vocalization, postures, chemical signals, even touch.

A crocodile’s brain is more complex than that of any other reptile. These powerful predators also have an excellent sense of smell and superior sound perception. Noting the crocís ability to learn to avoid dangerous situations, researchers have found that they have to modify their techniques when capturing crocs. It’s very hard to catch a croc twice with the same trick.

Crocodiles have demonstrated behavioral, physiological and structural adaptations that have allowed them to thrive for hundreds of millions of years, but, unfortunately, surviving human encroachment may be their biggest challenge ever. Through habitat enhancement and environmental education, humans may be able to ensure that these once endangered prehistoric reptiles practice their sophisticated survival skills for years to come.