Name: ___________________________Period: _______dramatically. Geologists were suggesting that Earth was ancient and had changed over time. Biologists were suggesting that life on Earth had also changed. The process of change over time is called evolution. Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors. Darwin’s journey began in 1831, when he was invited to sail on the HMS Beagle’s five-year voyage along the route shown in Figure 16–1.

1. What theory did Darwin develop? __________________________________________________________________________________________________

If you think evolution is just about explaining life’s ancient history, you might wonder why it’s so important. But Darwin’s work offers vital insights into today’s world by showing how the living world is constantly changing. That perspective helps us understand modern phenomena like drug-resistant bacteria and newly emerging diseases like avian flu.

2. Give an example how the modern world is constantly changing. _____________________________________________________________________________

A collector of bugs and shells in his youth, Darwin had always been fascinated by biological diversity. On his voyage, the variety and number of different organisms he encountered dazzled him. In a single day’s trip into the Brazilian forest, he collected 68 species of beetles, and he wasn’t particularly looking for beetles! Darwin filled his notebooks with observations about the characteristics and habitats of the different species he saw. But Darwin wasn’t content just to describe biological diversity (biological diversity refers to the variety or assortment of living things such as plants, animals, and microorganisms). He wanted to explain it in a scientific way. He kept his eyes and mind open to larger patterns into which his observations might fit. As he traveled, Darwin noticed three distinctive patterns of biological diversity: (1) Species vary globally, (2) species vary locally, and (3) species vary over time.

3. What were Darwin’s three patterns of diversity he noticed? ______________________________________________________________________________

Darwin visited a wide range of habitats on the continents of South America, Australia, and Africa and recorded his observations. For example, Darwin found flightless,

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Name: ___________________________Period: _______ground-dwelling birds called rheas living in the grasslands of South America. Rheas look and act a lot like ostriches, see Figure 16-2. Yet rheas live only in South America, and ostriches live only in Africa. When Darwin visited Australia’s grasslands, he found another large flightless bird, the emu. Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe.

There were other puzzles, too. For example, Darwin found two species of rheas living in South America. One lived in Argentina’s grasslands and the other in the colder, harsher grass and scrubland to the south. Darwin noticed that different, yet related, animal species often occupied different habitats within a local area.In addition to collecting specimens of living species, Darwin also collected fossils, which scientists already knew to be the preserved remains or traces of ancient organisms. Some fossils didn’t look anything like living organisms, but others did. Darwin noticed that some fossils of extinct animals were similar to living species. One set of fossils unearthed by Darwin belonged to the long-extinct glyptodont, a giant armored animal. Currently living in the same area was a similar animal, the armadillo. You can see in Figure 16–3 that the armadillo appears to be a smaller version of the glyptodont. So, why had glyptodonts disappeared? And why did they resemble armadillos?

4. What are fossils? ________________________________________________5. Explain Figure 16-3. _________________

_____________________________________________________________________________________________________________________________________________________________________

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Name: ___________________________Period: ________________________________________

Population GrowthIn 1798, English economist Thomas Malthus noted that humans were being born faster than people were dying, causing overcrowding, as shown in Figure 16–4. Malthus reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone. The forces that work against population growth, Malthus suggested, include war, famine, and disease.

Darwin realized that Malthus’s reasoning applied even more to other organisms than it did to humans. A maple tree can produce thousands of seeds each

summer. One oyster can produce millions of eggs each year. If all the descendants of any species survived for several generations, they would overrun the world. Obviously, this doesn’t happen; most offspring die before reaching maturity, and only a few of those that survive manage to reproduce. When Darwin realized that most organisms don’t survive and reproduce he wondered which individuals survive … and why.

6. How are organisms’ population controlled? ____________________________________________________________________________________________

Evolution by Natural SelectionDarwin realized that if more individuals are produced than can survive, members of a population must compete to obtain food, living space, and other limited necessities of life. Darwin described this as the struggle for existence. But which individuals come out on top in this struggle? Here’s where individual variation plays a vital role. Darwin knew that individuals have natural variations among their heritable traits. He hypothesized that some of those variants are better suited to life in their environment than others. Members of a predatory species that are faster or have longer claws or sharper teeth can catch more prey. And members of a prey species that are faster or better camouflaged can avoid being caught.

7. Describe Darwin’s struggle for existence. ____________________________________________________________________________________________

Any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment is called an adaptation. Adaptations can involve body parts or structures, like a tiger’s claws; colors, like those that make camouflage or mimicry possible; or physiological functions, like the way a plant carries out photosynthesis. Many adaptations also involve behaviors, such as the complex

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Name: ___________________________Period: _______avoidance strategies prey species use. Examples of adaptations are shown in Figure 16–5.

8. What are adaptations? Give an example. _____________________________________________________________________________________________________________________________________________________________________

According to Darwin, differences in adaptations affect an individual’s fitness. Fitness describes how well an organism can survive and reproduce in its environment. Individuals with adaptations that are well suited to their environment can survive and reproduce and are said to have high fitness. Individuals with characteristics that are not well suited to their environment either die without reproducing or leave few offspring and are said to have low fitness. This difference in rates of survival and reproduction is called survival of the fittest. In evolutionary terms, survival means reproducing and passing adaptations on to the next generation.

9. Define fitness. _________________________________________________________________________________________________________________

10.How does an individual have high fitness? _____________________________________________________________________________________________

Darwin named his mechanism for evolution natural selection. Natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring. In both artificial and natural selection, only certain individuals in a population produce new individuals. But in natural selection, the environment—not a farmer or animal breeder, as in artificial selection—influences fitness. When does natural selection occur? Natural selection occurs in any situation in

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Name: ___________________________Period: _______which more individuals are born than can survive (the struggle for existence), there is natural heritable variation (variation and adaptation), and there is variable fitness among individuals (survival of the fittest). Well-adapted individuals survive and reproduce. From generation to generation, populations continue to change as they become better adapted, or as their environment changes. Figure 16–6 uses a hypothetical example to show the process of natural selection. Notice that natural selection acts only on inherited traits because those are the only characteristics that parents can pass on to their offspring.

11.Define natural selection. ___________________________________________ ______________________________________________________________

12.Explain how Figure 16-6 illustrates natural selection. ____________________________________________________________________________________________________________________________________________________________

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Name: ___________________________Period: _______Just as well-adapted individuals in a species survive and reproduce, well-adapted species survive over time. Darwin proposed that, over many generations, adaptation could cause successful species to evolve into new species. He also proposed that living species are descended, with modification, from common ancestors—an idea called descent with modification. Notice that this aspect of Darwin’s theory implies that life has been on Earth for a very long time—enough time for all this descent with modification to occur! For evidence of descent with modification over long periods of time, Darwin pointed to the fossil record. Darwin based his explanation for the diversity of life on the idea that species change over time.

13.What is descent with modification and what evidence did Darwin use to support this theory?__________________________________________________________________________________________________________________________________

To illustrate this idea, he drew the very first evolutionary tree - an example is shown in Figure 16–7. This “tree-thinking” implies that all organisms are related. Look back in time, and you will find common ancestors shared by tigers, panthers, and cheetahs. Look farther back and you will find ancestors that these felines share with dogs, then horses, and then bats. Farther back still is the common ancestor that all mammals share with birds, alligators, and fish. Far enough back are the common ancestors of all living things. According to the principle of common descent, all species—living and extinct—are descended from ancient common ancestors. A single “tree of life” links all living things.

14.What does the principle of common descent propose? ___________________________________________________________________________________

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Name: ___________________________Period: _______

Natural Selection Pre-LabWhat are some differences you’ve noticed in the size and shape of dogs in your neighborhood?

Do their differences make them better at some things, but not well-suited for others (give examples)?

What would happen if the world suddenly changed, so the only thing that dogs could eat was deer and there was absolutely no way for a dog to eat if it wasn’t big or strong enough to catch and kill a deer?

Most likely, smaller dogs would die off, and the bigger ones would survive and reproduce. After a while, instead of a population of dogs of all sizes, most of the dogs in the population would be big dogs.

Next, think about the mice shown below.

Describe what is happening to the mice as time passes from figure 1 to figure 3.

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Name: ___________________________Period: _______

Living things that are well adapted to their environment survive and reproduce. Those that are not well adapted don’t survive and reproduce. An adaptation is any characteristic that increases fitness, which is defined as the ability to survive and reproduce.

Below are descriptions of four female mice that live in a beach area that is mostly tan sand with scattered plants.

Color of fur Brown Tan Tan and Brown

Cream

Age at death 2 months 8 months 4 months 2 months

# pups produced by each

female

0 11 3 0

Running speed 8 m/min. 6 m/min. 7 m/min. 5 m/min.

According to the definition given for fitness, which mouse would biologists consider the fittest? Explain why this mouse would be the fittest.

If a mouse's fur color were generally similar to its mother’s color, what color fur would be most common among the pups?

A more complete definition of fitness is the ability to survive and produce offspring who can also survive and reproduce. Below are descriptions of four male lions.

Name George Dwayne Spot Tyrone

Age at death 13 years 16 years 12 years 10 years

# cubs fathered 19 25 20 20

# cubs surviving to adulthood

15 14 14 19

Size 10 feet 8.5 feet 9 feet 9 feet

According to this definition of fitness, which lion would biologists consider the “fittest”? Explain why.

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Name: ___________________________Period: _______Suppose that Tyrone had genes that he passed on to his cubs that helped his cubs to resist infections, so they were more likely to survive to adulthood. These genes would be more common in the next generation, since more of the cubs with these genes would survive to reproduce. A characteristic which is influenced by genes and passed from parents to offspring is called heritable.

Over many generations heritable adaptive characteristics become more common in a population. This process is called evolution by natural selection. Evolution by natural selection takes place over many, many generations.

Evolution by natural selection leads to adaptation within a population. The term evolution by natural selection does not refer to individuals changing, only to changes in the frequency of adaptive characteristics in the population as a whole. For example, for the mice that lived in the beach area with tan sand, none of the mice had a change in the color of their fur; however, due to natural selection, tan fur was more common for the pups than for the mother mice.

In summary, a heritable characteristic that helps an animal or plant to have more offspring which survive to reproduce will tend to become more common in a population as a result of evolution by natural selection.

Questions

1. Explain why a characteristic which helps an animal to live longer will generally tend to become more common in the population as a result of evolution by natural selection.

2. Not all characteristics which contribute to longer life become more common in the population. Some characteristics contribute to long life, but not more offspring. For example, a female cat, which is sterile and cannot have any offspring, may live longer because she will not experience the biological stresses of repeated pregnancies. Explain why a characteristic like this which contributes to a long life, but with few or no offspring, would not become more common as a result of evolution by natural selection.

Candy Corn Evolution LabThis activity demonstrates one mechanism for evolution through a simulation that models the principles of natural selection. It helps answer the questions: How might biological change have occurred and been reinforced? Differential survival and reproduction of organisms is due to a variety of environmental factors such as predator-prey relationships, resource shortages, and changes of habitat.

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Name: ___________________________Period: _______ObjectivesStudents will understand the concepts:

1. Species evolve over time2. How natural selection works on a population3. Determine which organisms are more or less fit

Materials Box of candy corn M&M’s – 30 of each color: orange, yellow, brown, red, blue and green Stop Watch

Procedure1. Select a student to be the “Game Warden”. The game warden will count the

number of M&M’s of each color and record this data in the table. Start with 7 M&M’s of each color. These M&M’s represent the “Beginning Population,” and then randomly dispurse these M&M’s in the candy corn habitat.

2. The other group member is the “M&M Predator”. The game warden will present the box of candy corn and M&M’s to the predator, and the predator is to quickly glance into the box and retrieve all the observable M&M’s in 20 seconds, using both hands.

3. Once the “hunting” is complete, have the warden count the number of prey remaining in the habitat, (# of the color starting in habitat - # hunted = surviving prey) and record this number in the data table.

4. To simulate reproduction of offspring, double the amount of surviving M&Ms of each color and add these to the candy corn habitat. For example, if 6 blue M&M’s are remaining in the habitat after hunting, add 6 more to the habitat for a total of 12. 12 is now your beginning population for the 2nd Generation in the data table.

5. Repeat these steps for each generation.

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Name: ___________________________Period: _______Candy Corn Lab Results

Data: Number of Prey (M&M’s) in the Habitat at the Start of Each Generation

M&M

color

1st Generation 2nd generation 3rd Generation

Beginning

population

Hunted

Survived

After reproductio

n

Hunted Survived

After Reproductio

n

Hunted Survived

Blue 7

Brown 7

Green 7

Orange 7

Red 7

Yellow 7

Analysis Questions: WRITE USING COMPLETE SENTENCES!!!

1. Which prey items possessed the highest survival rate (use actual data)? Why do you think that these M&M’s (prey) survived at such a high rate?

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Analysis: Using the graph provided, graph your data using a line plot. X axis = generations, Y = number of M&Ms. Use colored pencils as your key (if you do not have colored pencils design a key) Don’t forget a title!!

Name: ___________________________Period: _______2. What effect did capturing a particular color M&M have on the numbers of that

color in the following generations?

3. How are the survival rates of organisms in the environment and evolution by natural selection related? Support your answer with data from the graphs and tables.

4. How are predator populations affected by the changing frequency of prey population’s phenotypes?

5. If the candy corn habitat changed after the third generation, and you substituted it with “Tootsie Rolls”, make a hypothesis as to how the different color M&M populations would change.

6. Explain why evolution by natural selection cannot occur if the variation in a characteristic does not contribute to differences in fitness. Suppose, for example, that all the hunters in the simulation were blind-folded and could only find M&Ms by touch. Would you expect evolution by natural selection in the color of M&Ms and why?

7. How would you explain the expression “survival of the fittest” to help someone understand how natural selection actually functions?

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Natural Selection Pre-Lab - Mr. Lundgren's Science Site...

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