GRADE LEVEL: 5-8

TOPIC/SUBJECT MATTER: Life Science

TIME ALLOTMENT: One to two 45-minute class periods

OVERVIEW:

During this video-enhanced lesson, students will watch video segments from the NATURE film “The Secret World of Sharks and Rays” and learn about adaptations that have helped sharks and rays survive. Students will explore similarities and differences between sharks, rays and other fish. They will watch segments that provide information about physical features and behaviors that have helped sharks and rays survive, with specific attention paid to the angel, wobbegong and saw sharks and the electric, sting and manta rays. Students will work in small groups to research a specific type of shark or ray and share their findings with the class. Students will discover that different types of sharks and rays have different temperaments and diets and that some of the largest sharks and rays are the most gentle.

MEDIA RESOURCES

Video

Clip 1

Fish, Sharks and Rays: A comparison of fish, sharks and rays.

Clip 2

A Close Look at Sharks: A close look at angel, wobbegong and saw sharks and their survival techniques.

Clip 3

A Close Look at Rays: A close look at electric, sting and manta rays and their survival techniques.

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

Web sites

Ichthyology at the Florida Museum of Natural History

This site features a rich variety of information, games and photographs of a variety of fish, including sharks and rays. The following sections are recommended for this lesson:

• Sharks- This section features information, games and photographs of sharks.
• Biological Profiles- This section provides photographs and detailed information about specific sharks and rays, as well as other fish.

Kidzone Fun Facts for Kids: Sharks

This Web site features a variety of photographs, activities and facts about sharks.

National Geographic: Sharks
This Web site features many photos and facts about sharks, which can be used in this lesson.

Seaworld: Sharks and Rays

This site contains a variety of facts, photographs and diagrams of sharks and rays.

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
  • Behavior is one kind of response an organism can make to an internal or environmental stimulus. A behavioral response requires coordination and communication at many levels, including cells, organ systems, and whole organisms. Behavioral response is a set of actions determined in part by heredity and in part from experience.
  • 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.
• Populations and ecosystems

• Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some microorganisms are producers-they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.

• Diversity and adaptations of organisms
  • 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.

• 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 group of 2-3 students:

• Books, reference materials and/or computers to conduct research on sharks and rays.

For the class:

• A large sheet of paper or board and something with which to write.
• A photograph of a bull shark and a photograph of a whale shark. (See “Prep for Teachers” section for details.)
• One computer for the teacher with a digital projection system (to play video clips either downloaded or streaming from the Web).

OBJECTIVES

Students will be able to:

• Discuss similarities and differences between sharks, rays and other fish;
• Describe physical features and characteristics that have helped sharks survive, with specifics about angel, wobbegong and saw sharks;
• Provide details of physical features and characteristics that have helped rays survive, with specifics about electric, sting and manta rays;
• Explain that there are many different types of sharks and rays, with varied skills, physical features, temperaments and diets;
• Explain that some sharks and rays are harmful to humans, while others are not and provide specific examples of harmful and gentle species;
• Discuss that sometimes the largest species can be the most gentle;
• Provide detailed information about one species of shark or ray.

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 one photo of a whale shark and one photo of a bull shark to show the class. Make sure that the image of the whale shark is about 3 times larger than the bull shark. See the “Web sites” section above for a list of sites with shark photos.

Proceed to ACTIVITIES

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

Fish, Sharks and Rays

Clip 2

A Close Look at Sharks

Clip 3

A Close Look at Rays

Snowy owl with chicks during the summer. In wintertime, survival on Ellesmere becomes even more difficult.

Winter on Ellesmere Island is a far cry from the tranquil summer seen in White Falcon, White Wolf. As the most Northern part of Canada and extending into the Arctic Circle, Ellesmere Island experiences extreme winters. Shrouded in continual darkness, temperatures reach beyond “cold” to a bitter -20 or -30 degrees Fahrenheit. To survive in these harsh conditions, animals must develop special adaptations to stay warm, conserve energy, and find food in a barren, frozen world.

To stay warm, most animals rely on their thick winter coats. Some of these coats can be quite “high tech.” Polar bears have a watertight layer of insulating hairs, protected by a layer of longer guard hairs on top.  Other Arctic animals rely on a similar layered coat where guard hairs act as a protective shield against the elements. Arctic foxes, for example, have furry feet. The hairs on the soles of their feet help them retain heat as they trot across the tundra.

The ultimate goal of all arctic animals is to lose as little body heat as possible. In comparison to their cousins, the red foxes, arctic foxes have several morphological differences. The first, of course, is their coat color. Their coats change to all white as the winter begins, then turn brown again the next summer to allow for seasonal camouflage. Arctic foxes also have a rounder body, shorter legs, shorter tails, shorter muzzles, and shorter ears. These are adaptations common to Arctic animals. The more compact the body, the less heat is lost.

Besides physical features like fur and body proportions, Arctic animals have highly specialized thermoregulatory systems. The metabolisms of Arctic animals can adjust seasonally so that animals conserve energy during the winter. Arctic animals have to be able to adjust their systems to cope with lower caloric intakes, or even to go without food for long periods of time. To do so, animals must make the most out of what they can find during the winter. The musk ox, like most Arctic animals, does what it can to fatten up during the summer when food is abundant. During the winter when food is less accessible and less nutritious, musk ox rely on these fat reserves to help them avoid starvation. It can be difficult to find food during the winter. Plants exist in a dormant state between the frozen ground and the blanket of snow. The air trapped between these two layers acts as insulation, and the plants and lichen living under the snow mostly avoid freezing temperatures. But any creature that eats this winter vegetation must first be able to get at it. Musk ox and caribou dig through the snow with their hooves and horns, or graze in windswept areas where food is exposed.

What it takes to survive on Ellesmere Island today may be vastly different in the years to come. Climate change and global warming are already altering the landscape. Massive ice shelves larger than the island of Manhattan, and thousands of years old, are breaking off from the northern edge of Arctic Canada. Glaciers are retreating, and the average winter temperature is increasing. Most animals on Ellesmere Island are so well adapted to life in the Arctic that any change in climate could be catastrophic. Only time can tell what will happen to the handful of specialized animals that call Ellesmere home during winter.

For further information on climate change and the Arctic, visit our list of additional web and print resources.

Photo © Mark Smith 2007

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.

Uncertain Future for the Alpine Red Deer

However inhospitable the weather may turn in the highest regions of the Austrian Alps, evolution has equipped the diverse species that claim these heights as their home with the ability to survive. The variations in weather are often sudden and intense, and the adaptations and perseverance required of these alpine creatures in order to ensure species survival are remarkable.

Throughout the year, Austria’s red deer roam the alpine environment in search of food. In summer, the red deer migrate to the highest altitudes and can stay there all season long. But, over the course of the season, the force of the elements can vary widely. Frequent lightning strikes can decimate entire herds that frequent these regions. If the mountain grasslands go dry or are over-grazed by local herds, the red deer will move down the mountainside to lower pastures where there may be more vegetation.

Come autumn, the red deer descend to lower elevations in the forested river valleys and graze on vegetation there before the long, grueling winter. When winter arrives, the landscape is transformed. Snow accumulation can exceed a person’s height in just a few days. Red deer forage for the sparse remaining vegetation on the cliffs, where winds have cleared the snow and left patches of plant life. The strongest deer are able to adapt and reduce their need to eat in winter. As they take in fewer calories, their heart rate, body temperature and metabolism are drastically lowered, and they slow down to reduce their energy expenditure.

In winter, snow accumulation can exceed a person’s height in just a few days.

Humans are changing everything and disrupting the process of natural selection. Many deer in the Alps can no longer survive the seasons on their own because they have come to depend on handouts from local landowners, farmers and even hunters who put out food to attract the deer. Austria’s red deer management program, too, in an effort to keep deer populations large enough to guarantee hunting success, have set up feeding stations in fenced enclosures near roads, where many deer spend more than half the year.

Each year it gets more difficult for the red deer to fend for themselves as humans encroach on their terrain. Busy roads, hunting stations, eco-unfriendly ski resorts, and the effects of global warming are threatening the long-term stability of red deer populations.

Along with the fenced enclosures for feeding, roads and highways are disrupting the deer’s migration route. More than 10 million trucks and about 50 million cars cross the Alps each year. Seventy-seven million tons of cargo move through the mountains in an average year, including furniture, chemicals, livestock, mineral water and automobiles. By 2020, some predict, Trans-Alpine commercial transport will double. The mountains concentrate the fumes from all these vehicles, and the greenhouse gas emissions are trapped in narrow valleys. The rapid increase in these carbon-emitting fossil fuels is expected to have a profound effect on the climate of the Alps. For the red deer, the problem is that they have adapted to the cold, barren conditions of Austria’s Alpine region. Biologists fear that if the temperature keeps rising, many alpine animals will face quick declines or extinction. According to the Austrian Central Institute for Meteorology and Geodynamics, the Alps are warmer today than anytime in the past 1,300 years. Some creatures have adapted to the constantly changing and gradually more restrictive environment — shifting breeding and migration dates, according to Science Magazine. But the red deer have fewer places to migrate, since they are surrounded by roads and ski resorts.

In 2007, Austria held an international conference on how to cope with the warm winters and lack of snowfall caused by global warming. However, the focus of the conference was not the animals and their habitat, but rather the impact of climate change on tourism and ski resorts. Austria’s Federal Forest Administration is working with land owners, communities and traffic authorities to protect wildlife corridors by building green bridges. And, ski resorts in the Alps are answering the demand for sustainable tourism by offering incentives for visitors who use public transportation and hybrid cars. But even with these green initiatives, it’s uncertain what lies ahead for these mountain dwellers when human encroachment and global warming threaten their natural resources and habitat.

We — and every other organism on earth — are only young once. But childhood may be the most important part of our lives, the time when we learn the skills that will help us survive for the rest of our years.

A face that, perhaps, only a mother could love. NATURE’s Baby Tales takes a serious but playful look at childhood in the animal kingdom. There are plenty of cute baby pictures, from the heart-melting face of a trembling calf to the toothy grin of a newborn alligator — a face only a mother could love.

While some — such as chimpanzees and elephants — may spend years with mom or dad, others — such as sea turtles and many insects — never know their parents, and must fend for themselves from the moment of birth.

Exactly how these newborns learn to survive isn’t completely understood. Some important behaviors, such as knowing how to head for the sea and not to climb higher on the beach, are somehow encoded in the animal’s genes. But youngsters also learn how to hunt and defend themselves by watching their parents and siblings. And scientists believe that some animals — from cats to crows — learn important survival skills by just playing.

Yes, that lion cub swatting at its sister, that puppy chewing on a stick, and that group of kids playing tag may be gaining important life experience. The lion, for instance, may be learning how to hunt, while the puppy strengthens its teeth. And the kids are learning important lessons in rule-making and cooperation.

A face that, perhaps, only a mother could love.

But researchers have long differed on the role of play in a young animal’s life. Many biologists, for instance, once believed that play is not a distinct form of behavior, and dismissed it as a purposeless collection of activities that had no benefit to the animal. Increasingly, however, researchers believe that many animals not only engage in play to learn skills, but because it brings them pleasure and is key to social development

In studies of rats, for instance, Columbia University researcher Susan Brunelli discovered that playful infants made better parents than those that didn’t play. Other studies have shown that cats, rats, and mice that goof around as youngsters have better developed brains and muscles than those who lived more boring lives. Indeed, these animals tend to play the most when key organs and tissues are developing quickly. Other research suggests that play helps youngsters burn off excess energy and weight, and stay cozily warm.

Play helps cement animal relationships. Most animals that exhibit playful behavior are birds or mammals that live highly social lives. Play helps cement their relationships. But some observers believe insects and other invertebrates may play too. The great evolutionary biologist Charles Darwin, for instance, reported in the 1800s that naturalists observed what they believed to be playing ants — tiny crawlers that nipped and chased each other for no apparent reason.

Most modern scientists doubt that playing ants exist. But more recently, researchers have suggested that octopuses might amuse themselves with games. In an unusual experiment, biologists Jennifer Mather of the University of Lethbridge in Alberta, Canada, and Roland Anderson of the Seattle Aquarium gave eight octopuses empty plastic pill bottles. At first, each animal grabbed the bottle and “tasted” it, seeing if it was good to eat. Then, several of the animals began pushing the bottles around with jets of water, with two of them “playing” with the bottles for at least 10 minutes. “If a human were doing this, someone might say we were bouncing a ball,” Mather told reporters.

Of course, it’s hard to know if the animals were amused or just practicing some arcane prey-catching skill. Either way, researchers say its worth paying more attention to how animals — particularly babies — spend their free time. Play may provide “promising evidence of animal minds,” says Marc Bekoff, a leading play researcher at the University of Colorado. It would be unfortunate, he says, “if people decided that just because play was difficult to study, it was impossible to study.”

Producer: Ronnie Godeanu

Design Director: Sabina Daley

Designer: Lenny Drozner

Writer: David Malakoff

Animation: Lenny Drozner, Radik Shvarts

Page Building: Brian Santalone

Production Artists: Leela Corman, Meiza Fleitas

Production Assistant: Peter Tierney

Technical Director: Brian Lee

Scientific Consultant: Gianna Savoie

Thirteen Online is a production of Thirteen/WNET New York’s Kravis Multimedia Education Center in New York City. Anthony Chapman, Director of Interactive & Broadband. Carmen DiRienzo, Vice President and Managing Director, Corporate Affairs.

© 2001 Thirteen/WNET New York

All Rights Reserved

About the Writer

David Malakoff is a journalist covering research discoveries and the politics of science for SCIENCE MAGAZINE in Washington, D.C. His writing has appeared in a wide range of venues, including THE ECONOMIST, THE WASHINGTON POST, and ABCNews.com. He lives with his wife and three children — NATURE lovers all — in Alexandria, Virginia.

Television Credits:

A co-production of Green Umbrella Ltd., Thirteen/WNET New York, Trebitsch Produktion International GmbH, and Devillier Donegan Enterprises

Funder Credits

Funding for the TV series NATURE is made possible in part by Park Foundation. Major corporate support is provided by Canon U.S.A., Inc., Ford Motor Company, and TIAA-CREF. Additional support is provided by the nation’s public television stations.

In a mountain rainforest on the island of Trinidad, at the narrow entrance to a deep and noxious cave, TRIUMPH OF LIFE series producer Nick Upton and cameraman Jim ClarBatse prepare for an unusual challenge. Several hundred thousand bats, including vampire bats, live in the cave, along with millions of other creatures. When darkness comes, the bats will rush to fill the night sky. Upton’s goal is to film this fantastic exodus from inside the cave. The results are on view in the six-part NATURE series TRIUMPH OF LIFE.

From Nick Upton’s Diary:

“This is our sixth day at the cave. With luck, it will be our last and we can move on. I won’t miss lugging the equipment up that mountain terrain, and then lowering it piece by piece on a rope down a 30-foot shaft into the caveBats. But that isn’t the worst of it. When Jim and I need to clear our access ladder for a scene, we’ve had to enter the cave through the squeeze hole — an incredibly narrow passage that you have to wriggle through feet first. It bends in the middle and ends in a four-foot drop into piles of bat guano. It’s no joke, especially for a six-foot-three, 210-pounder like me. I’ve come close to getting stuck more than once. And all the while you’re maneuvering, bats are fluttering near your face and the cockroaches are skittering along the walls. We did this as many as six times some nights. Once, when I was about halfway through the squeeze-hole by myself, I knocked out the battery of my head-lamp and was stranded in total darkness. It took several jittery minutes to reinsert the battery and reconnect its wires by touch. Of course, I knew Jim would look for me eventually, but being wedged in solid rock with all that life teeming around me in the darkness made those minutes feel like hours.”

Night of the Guano

“The darkness, however, is by no means the only threatening aspect of this environment. The extreme heat and humidity are stifling, and the air is acrid with gases rising off the huge heaps of guano. Inhaling fungal spores in the air can cause a serious disease called histoplasmosis, so we wore face masks all the time. As for the creatures that share the cave with the bats, most are harmless, even the creepy-looking whip scorpions. But it’s essential to watch out for the poisonous snakes. The intense heat means that protective clothing is out, and one night I was bitten by a blood-sucking bug that sometimes carries a debilitating disease. But I managed to dislodge it before it could really go to work.

“Despite all the creatures in the cave and the dangers of navigating it, one thing above all else stands out as the most objectionable aspect of this underground environment — it seethes with millions of four-inch cockroaches. They live on the bat droppings and sometimes the ground actually seems to pulsate with them. In truth, the roaches aren’t really a physical danger, but they can be a bit disconcerting when they fly into you in the dark or crawl under your shirt.”

Rescuing the Pups

“Perhaps this will surprise some viewers, but the bats pose no danger either. BatsAnd that’s just as well, because in a few moments, Jim and I and a camera will be positioned between the cave’s exit and the third of a million bats that will fly past us at full speed. This should allow us to capture an amazing spectacle. So far, we’ve recorded some truly intimate aspects of bat behavior, such as feeding, breeding, and the dramatic rescuing of bat pups that fall from the roof of the cave by ‘baby-sitter’ bats. Until now, this fascinating behavior had been witnessed only by a handful of researchers. Capturing these scenes required a subtle touch. We used an infrared filming system to avoid disturbing the bats, and spent five long days in the cave, working in total darkness most of the time.

caption goes here

“However, the bats aren’t nearly so sensitive leaving the cave, and so for this scene we’ll use normal filming lights, powered by a large generator, which, by the way, we and our guide had to drag up the mountain, nearly killing ourselves.”

Exodus

“The sun has gone down, and already we can hear thousands of bats flitting around in a deeper portion of the cave, calling loudly. The charge is about to begin, and Jim and I have done all we can to prepare ourselves. And here they come, directly towards us, whizzing by our faces by the hundreds at first, then quickly by the thousands, the tens of thousands, the hundreds of thousands — pouring out into the night through the narrow exit. On and on it goes, for 40 heart-stopping minutes. But it seems like only five minutes to us, as we frantically switch lenses, change camera positions, adjust the lights, and record the eerie sounds.

“This is our chance to record this moment forever. It has been one of the most amazing experiences of my life — an entire civilization of bats swooping past us just inches away. And what an unforgettable demonstration of the astounding accuracy of their sonar abilities, for not one bat ever struck us! For the unique achievement inside that cave, I have the greatest admiration for my long-suffering cameraman. Jim seemed totally unfazed by the conditions; but then, he’s one of the real ‘hard men’ of wildlife filmmaking. As for me, despite all the hard work and discomfort, I find myself lookingBat forward to returning here some day. There is much more to film and to learn. Bats are remarkable animals, far more intelligent and sociable than people realize. I feel privileged to be in their strange, underground world and to have the opportunity to share the experience with the viewers of NATURE.”

A Powerful Organ Hearts, eyes, flippers and wings — evolution has forged many remarkable body structures. But none is more amazing than the brain, that bundle of nerve cells that allows us to sense our surroundings, sort out information, and make decisions. Indeed, the great importance of BRAIN POWER to evolution is the subject of this week’s installment of NATURE’s TRIUMPH OF LIFE series.

Brains are not essential to life. Many organisms, from algae to jellyfish, get along just fine without a central information-processing center. But there is no question that a brain gives many animals an edge. For in the struggle for survival, brawn often gives way to a brain that can outthink a competitor.

Not all brains are equal, however. Some brains consist of just a few hundred or few thousand cells, just enough to sense changes in light or temperature, or to sniff out important smells. Others, like ours, contain billions of cells, enabling everything from language to tool-making.

But simple is often more than enough to assure an animal’s survival. A flatworm’s basic brain, for instance, helps it sniff out earthworms, making the worm a lethal hunter. And while a honeybee’s brain is bigger than a flatworm’s, it is still not all that complex. Nonetheless, the bee is capable of amazing feats of memory, as BRAIN POWER shows.

In their short two-month lives, worker bees must learn to remember where nectar-producing flowers are located in relation to the hive, and exactly what time of day they produce the sweet liquid. The life-or-death memorization is aided by an amazing change in the bee’s brain: as it needs to retain more information, the brain grows, adding tens of thousands of cells on an as-needed basis! Once, scientists believed that such brain-changing abilities were limited to just a few animals. In recent years, however, evidence has shown that many animals’ brains are more flexible than once thought possible. Some birds, for instance, grow new brain tissue during the breeding season — perhaps to sing more complex songs — then lose the cells once mating is over. Other bird brains grow or shrink for migration.

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Watch this clip to find out how a bee’s brain can sense changes in time.

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Researchers have even had to rethink their views of the human brain. Once, they believed that our brains grew only during childhood. It was believed that once we reached adulthood, we only lost — and never gained — brain cells. But surprising new studies show that we continue to add some kinds of brain cells throughout life. And other research shows that although our brains are usually very specialized, with particular parts responsible for certain activities, the human brain can sometimes reorganize itself. People who have lost speech or coordination due to stroke or brain injuries, for instance, can sometimes regain those abilities by “training” a new part of the brain to take over. Such findings have raised new hopes for treating serious brain injuries and birth defects.

Scientists, however, are still puzzling over the question of why we evolved such big, complex brains. Clearly, they are a big help in outsmarting predators and finding food. But our brains may also be a product of social pressures. We expend enormous energy in forging complex social relationships and alliances, whether within a family, among neighbors, or among nations. Making these relationships work requires creative thinking, constant problem-solving, and the ability to understand how another person is thinking — all tasks that call for some serious brain power. Over time, evolution favored those individuals with the best social and survival skills.

For the moment, our brains have made us the most influential species on earth. Our tool-making skills have allowed us to reconstruct the landscape, building cities and plowing fields where forests and grasslands once reigned. We’ve figured out how to make the desert bloom, pumping water from far below the earth to quench our thirsts. And, unintentionally, we may even be altering the planet’s climate by burning massive quantities of coal, oil, and wood that produce carbon dioxide and other global warming gases.

It remains to be seen, however, whether even our brainpower will help us avoid the fate of so many other species in Earth’s history: extinction.