Unit 1-2 Theory of Evolution by Natural Selection PDF

What did Darwin observe? Charles Darwin was born in England in 1809. When he was 22 years old, Darwin graduated from college with a degree in theology. But he was also interested in plants and animals. Darwin became the naturalist -a scientist who studies nature- on the British ship HMS Beagle....

What did Darwin observe? Charles Darwin was born in England in 1809. When he was 22 years old, Darwin graduated from college with a degree in theology. But he was also interested in plants and animals. Darwin became the naturalist -a scientist who studies nature- on the British ship HMS Beagle. During his voyage, Darwin observed and collected many living and fossil specimens. He made some of his most important observations on the Galápagos Islands of South America. He kept a log that was later published as “The Voyage of the Beagle”. With the observations he made on this almost five-year journey, Darwin formed his idea about how biological evolution could happen. In biology, “evolution” refers to the process by which populations change over time. A population is all of the individuals of a species that live in an area at the same time. A species is a group of closely related organisms that can mate to produce fertile offspring. Darwin developed a hypothesis, which eventually became a theory, of how evolution takes place. A) Differences among Species Darwin collected birds from the Galápagos Islands and nearby islands. He observed that these birds differed slightly from those on the nearby mainland of South America. And the birds on each island were different from the birds on the other islands. Careful analysis back in England revealed that they were all finches! Eventually, Darwin suggested that these birds may have evolved from one species of finch. Darwin observed differences in beak size among finches from different islands. Many years later, scientists confirmed that these differences related to the birds' diets. Birds with shorter, heavier beaks could eat harder foods than those with thinner beaks. What other ideas influenced Darwin? The ideas of many scientists and observations of the natural world influenced Darwin's thinking. Darwin drew on ideas about Earth's history, the growth of populations, and observations of how traits are passed on in selective breeding. All of these pieces helped him develop his ideas about how populations could change over time. A) Organisms Pass Traits On to Offspring Farmers and breeders have been producing many kinds of domestic animals and plants for thousands of years. These plants and animals have traits that the farmers and breeders desire. A trait is a form of an inherited characteristic. For example, the length of tail feathers is an inherited characteristic, and short or long tail feathers are the corresponding traits. The practice by which humans select plants or animals for breeding based on desired traits is artificial selection. Artificial selection shows that traits can change. Traits can also spread through populations. B) Organisms Acquire Traits Scientist Jean-Baptiste Lamarck thought that organisms could acquire and pass on traits they needed to survive. For example, a man could develop stronger muscles over time. If the muscles were an advantage in his environment, Lamarck thought the man would pass on this trait to his offspring. Now we know that acquired traits are not passed on to offspring because these traits do not become part of an organism's DNA. But the fact that species change, and the idea that an organism's traits help it survive, shaped Darwin's ideas. C) Earth Changes over Time The presence of different rock layers, such as those in the photo, show that Earth has changed over time. Geologist Charles Lyell hypothesized that small changes in Earth's surface have occurred over hundreds of millions of years. Darwin reasoned that if Earth were very old, then there would be enough time for very small changes in life forms to add up.  D) A Struggle for Survival Exists After his journey, Darwin read an essay about population growth by economist Thomas Malthus. The essay helped Darwin understand how the environment could influence which organisms survive and which organisms die. All populations are affected by factors that limit population growth, such as disease, predation, and competition for food. Darwin reasoned that the survivors probably have traits that help them survive and that some of these traits could be passed on from parent to offspring. What are the four parts of natural selection? Darwin proposed that most evolution happens through the natural selection of advantageous traits. Natural selection is the process by which organisms that inherit advantageous traits tend to reproduce more successfully than other organisms do. There are four parts that contribute to the process of evolution by natural selection- overproduction, genetic variation, selection, and adaptation. A) Overproduction When a plant or animal reproduces, it usually makes more offspring than the environment can support. For example, a female jaguar may have up to four pups at a time. Across the jaguar population, only some of them will survive to adulthood, and a smaller number of them will successfully reproduce. B) Genetic Variation Within a population there are natural differences, or variations, in traits. For example, in the two jaguar skulls to the left, one has a larger jaw than the other. This difference results from a difference in the genetic material of the jaguars. Genetic variations can be passed on from parent to offspring. An important source of variation is a mutation, or change in genetic material. With each new generation, genetic variation introduces changes to the traits of a population. Greater genetic variation in a population increases the chance that some individuals will have traits that can help them survive environmental changes or diseases. Traits that enhance an individual's ability to reproduce will also increase the chance of survival of a species.  C) Selection Individuals try to get the resources they need to survive. These resources include food, water, space and, in most cases, mates for reproduction. About 11,000 years ago, jaguars faced a shortage of food because the climate changed and many prey species died out. A genetic variation in jaw size then became important for survival. Jaguars with larger jaws could eat hard-shelled reptiles when other prey were hard to find. Individuals with a particular trait, such as a large jaw, are more likely to survive long enough to reproduce. As a result, the trait is "selected" for, becoming more common in the next generation of offspring. D) Adaptation An inherited trait that helps an organism survive and reproduce in its environment is an adaptation. Adaptation is the selection of naturally occurring trait variations in populations. Jaguars with larger jaws were able to survive and reproduce when food was hard to find. As natural selection continues, adaptations grow more common in the population with each new generation, and new adaptations may arise. Over time, the population becomes better adapted to the environment. How do species change over time? In order for a population to change, some individuals have to be genetically different from other members of the population. Mutations are one of the main sources of genetic variation. Offspring sometimes inherit a gene that has a slight mutation, or change, from the gene the parent has. Mutations can be harmful, helpful, or have no effect. Beneficial mutations help individuals survive and reproduce. A) Over Generations, Adaptations Become More Common Adaptations are inherited traits that help organisms survive and reproduce. At first, an adaptation is rare. For example, imagine a population of birds in which some birds have shorter beaks. If more birds with shorter beaks survive and reproduce than birds with longer beaks, more birds in the next generation will probably have short beaks. The number of individuals with the adaptation would continue to increase. Some adaptations, such as a duck’s webbed feet, are physical. Other adaptations are inherited behaviors that help an organism find food, protect itself, or reproduce.  B) Genetic Differences Add Up Parents and offspring often have small genetic differences between them. Over many generations, the small differences can add up. These differences accumulate so that organisms alive now are often very different from their ancestors. As a result, there is great diversity among organisms. For example, the antibiotic penicillin was able to kill many types of bacteria in the 1950s. Today, some of those species of bacteria are now completely resistant to penicillin. The genetic makeup of these bacterial populations has changed. New fossil discoveries and new information about genes add to scientists' understanding of natural selection and evolution. C) Adaptations Can Allow a Species to Survive All organisms have traits that allow them to survive in specific environments. For example, plants have xylem tissue that carries water up from the roots to the rest of the plant. If the environment changes, a species is more likely to survive if it has genetic variation. For example, imagine a species of grass in which some plants need less water than others. If the environment became drier, many grass plants would die, but the plants that needed less water might survive. These plants might eventually become a new species if they cannot reproduce with the plants that needed more water. What happens to species as the environment changes? Certain environments favor certain traits. Consider a snake population with either brown- or green-colored snakes. In a forest that has many dead leaves on the ground, brown snakes will blend in better than green snakes will. But in an area with more grass, the green snakes may be better at hiding from predators. Changes in environmental conditions can affect the survival of organisms with a particular trait. Environmental changes can also lead to diversity of organisms by increasing the number of species. A) Adaptations Can Allow a Species to Survive All organisms have traits that allow them to survive in specific environments. For example, plants have xylem tissue that carries water up from the roots to the rest of the plant. If the environment changes, a species is more likely to survive if it has genetic variation. For example, imagine a species of grass in which some plants need less water than others. If the environment became drier, many grass plants would die, but the plants that needed less water might survive. These plants might eventually become a new species if they cannot reproduce with the plants that needed more water. B) Some Species May Become Extinct If no individuals have traits that help them to survive and reproduce in the changed environment, a species will become extinct. Extinction occurs when all members of a species have died. Greater competition, new predators, and the loss of habitat are examples of environmental changes that can lead to extinction. Some extinctions are caused by natural disasters. Because a natural disaster can destroy resources quickly, organisms may die no matter what adaptations they have. The fossil record shows that many species have become extinct in the history of life on Earth. ******************************************************** - Because grass snake's skin color looks like the plant stalk, it is able to hide from predators! This form of camouflage is the result of natural selection. - The plants and animals on the Galápagos Islands differed from island to island. This is where Darwin studied birds called finches. - Darwin left England on December 27, 1831. He returned 5 years later. - Darwin saw many plants and animals that were found only on certain continents such as Australia. - These rock layers formed over millions of years. - Not all of these jaguar cubs will survive long enough to reproduce. - Variation exists in the jaw sizes of these two jaguars. This variation will be passed on to the next generation. - A larger jaw makes it easier for this jaguar to eat hard-shelled turtles. - Large jaw size is one adaptation of jaguars. - The male frigate bird uses his red throat pouch to attract a female, which could lead to reproduction. - Dinosaurs went extinct 65 million years ago. - Darwin's theory of natural selection was influenced by his own observations and the work of other scientists. - The theory of evolution by natural selection states that organisms with advantageous traits produce more offspring. - Many extinctions have occurred over the course of Earth's history. ***************************************************** - How do you think this bird and this flower are related? Explain your answer. - Give examples of adaptations. - Fur color can help prevent an animal from being eaten (True / False). - The amount of available food can affect an organism's survival (True / False). - Your parents' characteristics are not passed on to you (True / False). - A species can go extinct if its habitat is destroyed (True / False). - How do you think the pointed beak of this woodpecker finch helps it to get food? - What are the names of other important thinkers who influenced Darwin's ideas? - Darwin studied artificial selection in the pigeons that he bred. List three other domestic animals that have many different breeds. - Explain why the size of your muscles is partly an acquired trait and partly dependent on DNA. - Describe how butterfly's long mouth part helps it to survive. - Through )natural / artificial selection(, breeders choose the traits that are passed on to the next generation. - Natural selection can act only on (acquired traits / inherited variation). - Because of environmental change, dinosaurs eventually became (mutated / extinct). - Describe Darwin's observations on the Galápagos islands during his voyage on - the HMS Beagle. - How does environmental change affect the survival of a species? - Why are only inherited traits, not acquired ones, involved in the process of - natural selection? - Describe What is the relationship between mutation, natural selection, and adaptation? ***************************************************** - What can you conclude from the two red growth lines on this graph? ***************************************************** - What might be a natural reason for low survival rates of jaguar cubs? - How did large jaws and teeth become typical traits of jaguars? - ***************************************************** - Use the diagram to answer the following question. 1- How is each of these lizards adapted to its environment? 2- What might happen to a population of rabbits in a forest if a new predator moved to the forest?  ***************************************************** - In the table below, explain how each part of natural selection works. # Principle of natural selection How it works 1 overproduction 2 genetic variation 3 selection 4 adaptation ***************************************************** - Use the following terms to fill below blanks: (evolution / mutation / artificial selection / adaptation / natural selection / extinction / variation) 1- The four parts of natural selection are overproduction, ____________ , selection, and adaptation. 2- _________________ is the process by which populations change over time. 3- The hollow bones of birds, which keep birds lightweight for flying, is an example of a(n) _______________. ***************************************************** - Environmental change has affected the environmental conditions near the North Pole. 1- How has ice cover near the North Pole changed in the last few decades? 2- How do you think this environmental change will affect species that live in the surrounding area? - Trace Darwin’s route on the map, and choose one of the following stops on his journey: Galápagos Islands, Andes Mountains, Australia. Do research to find out what plants and animals live there. Then write an entry in Darwin’s log to describe what he might have seen.  ***************************************************** - You can often define an unknown word by clues provided in the sentence. Use the sentence below to make an educated guess about the meaning of the word artificial. Example sentence: Many people prefer real sugar to artificial sweeteners made by humans. artificial: ***************************************************** - This chicken has been bred to have large tail feathers and a big red comb. - This chicken has been bred to have large head feathers. - This chicken has been bred to have feathers on its feet. **************************************************** - Cactus finch has a narrow beak that it can use in many ways, including to pull grubs and insects from holes in the cactus. - Vegetarian finch has a curved beak, ideal for taking large berries from a branch. - Woodpecker finch.