u6 l1 theory of evolution by natural selection

Unit 6 Lesson 1 Theory of Evolution by Natural Selection

Copyright © Houghton Mifflin Harcourt Publishing Company


Indiana Standards


• 8.3.1 Explain that reproduction is essential for the continuation of every species and is the mechanism by which all organisms transmit genetic information.

• 8.3.5 Identify and describe the difference between inherited traits and physical and behavioral traits that are acquired or learned.


Indiana Standards


• 8.3.7 Recognize and explain that small genetic differences between parents and offspring can accumulate in successive generations so that descendants may be different from their ancestors.

• 8.3.8 Examine traits of individuals within a population of organisms that may give them an advantage in survival and reproduction in a given environments or when the environment changes.


Indiana Standards


• 8.3.9 Describe the effect of environmental changes on populations of organisms when their adaptive characteristics put them at a disadvantage for survival. Describe how extinction of a species can ultimately result.

• 8.3.10 Recognize and describe how new varieties of organisms have come about from selective breeding.

Darwin’s Voyage


What did Darwin observe?

• Evolution is the process in which populations gradually change over time.

• A scientist named Charles Darwin developed a theory of how evolution takes place.

• Darwin formed the theory with the observations that he had made on an almost five-year journey.



• On his journey, Darwin observed and collected many living and fossil specimens.

• Darwin made his most influential observations on the Galápagos Islands of South America.




• Darwin collected birds from the Galápagos Islands and nearby islands.

• The birds on each island were different from the birds on the other islands, and all were different from the birds on the mainland.

• Darwin wondered if the birds had evolved from one species of finch.



Darwin’s Homework


What other ideas influenced Darwin?

• Darwin was influenced by the ideas of many scientists. These helped him develop his theory about how populations change over time.

• Farmers and breeders select plants or animals for breeding based on desired traits. This is called artificial selection.

• A trait is a form of an inherited characteristic.



• Scientist Jean-Baptiste Lamarck thought that organisms could bring about the changes they needed to survive in the environment.

• He did not know that acquired traits do not become part of an organism’s DNA and the traits cannot be passed to the offspring.

• His idea that organisms’ traits help them survive influenced Darwin’s theory.




• Geologist Charles Lyell theorized that small changes in rock have collected 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 collect over a very long period of time as well.




• Darwin read an essay by Thomas Malthus that suggested populations are limited by food resources, disease, competition, and predation.




• Darwin reasoned that survivors probably had traits that helped them survive in their environment.

• Darwin thought that some of these traits would be inherited by the offspring of the survivors.



Natural Selection


What are the four parts of natural selection?• Natural selection is the process by which

organisms that inherit advantageous traits tend to reproduce more successfully.

• Plants and animals can overproduce, meaning that they make more offspring than the environment can support.

• Only some of them will successfully reproduce.


What are the four parts of natural selection?• Within a species there are natural differences, or

variations, in traits.

• Variations come from differences in genetic material and can make an individual better able to survive.

• Genetic variation is important for the survival of a species.



What are the four parts of natural selection?• Individuals of a species try to get the resources

they need to survive.

• Darwin reasoned that individuals with a certain trait might be more likely to survive long enough to reproduce.

• As a result, the trait is “selected,” or is more common in the next generation of offspring.



What are the four parts of natural selection?• An adaptation is an inherited characteristic that

helps an organism survive and reproduce in its environment.

• As natural selection repeats from generation to generation, these adaptations become more common.

• Over time, a population becomes better adapted to the environment.



Well-adapted


How do species change over time?

• An incredible diversity of life exists because species have changed over time, or evolved.

• Populations evolve by becoming better adapted to their environment by the process of natural selection.


How do species change over time?

• Sometimes a population changes so much that the population becomes a new species.

• Some of the adaptations that help species survive are behaviors that help them to find food, protect themselves, or reproduce.



Why is adaptation important for survival?• The traits that help an organism survive depend

on both the needs of the species and environmental factors.

• Different environments have different factors.

• A green snake has a better chance of surviving to reproduce in green grass than on a brown forest floor.



Why is adaptation important for survival?• Changes in environmental conditions can affect

the survival of individuals with a particular trait.

• If no individuals are born with traits that help them to survive and reproduce in the changed environment, the species will become extinct.



Why is adaptation important for survival?• Extinction is when all of the members of a

species have died.

• The fossil record shows that many species have become extinct in the course of the history of life on Earth.



u6 l1 theory of evolution by natural selection

Science

theory of evolution

charles darwin

organisms traits

populations of organisms

advantageous traits

desired traits

traits of individuals

organisms dna