Evolution and Natural Selection

Evolution and Natural Selection

Middle School

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Learning Objectives

• Explain Darwin's theory of evolution by natural selection.

• Describe the role of adaptation and variation in evolution.

• Differentiate between natural selection, artificial selection, and speciation.

• Identify the four key factors that drive natural selection.

Key Vocabulary

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Evolution

The gradual change in a species over many generations as it adapts to new environmental conditions.

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Natural Selection

The process where organisms better adapted to their environment tend to survive and produce more offspring.

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Adaptation

A trait that helps an organism survive and successfully reproduce in its specific environment.

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Fitness

A measure of how well an organism can survive and pass its genes on to its offspring.

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Speciation

The evolutionary process by which a new species of plant or animal is created from a group.

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Common Descent

The principle that all living organisms are derived from common ancestors and have changed over time.

Key Vocabulary

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Genetic Variations

Any difference between individuals of the same species, which is essential for natural selection to occur.

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Darwin's Journey and Key Observations

• In 1831, Charles Darwin began a five-year voyage on the HMS Beagle.

• He was amazed by the diversity of life on the Galapagos Islands.

• Island iguanas had large claws to grip rocks, unlike mainland iguanas.

• He also saw that tortoise shell shapes varied from one island to another.

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Multiple Choice

What did Charles Darwin find particularly amazing during his voyage to the Galapagos Islands?

• The fact that all iguanas had small claws.

• The similar shapes of all tortoise shells.

• The wide diversity of life he encountered.

• The five-year duration of his journey.

Multiple Choice

What did Darwin's comparison of island iguanas and mainland iguanas reveal?

• The island iguanas had different physical traits suited to their environment.

• The animals were identical in every way.

• The mainland iguanas had larger claws.

• The island iguanas were unable to grip rocks.

Multiple Choice

What general conclusion is supported by Darwin's observations of both the iguanas and the tortoises?

• Darwin's voyage on the HMS Beagle lasted for ten years.

• The physical characteristics of animals can differ from one location to another.

• Animal species look the same no matter where they live.

• All tortoises on the Galapagos Islands have the same shell shape.

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Adaptation and the Dawn of a Theory

• Darwin saw that Galápagos finches had beaks adapted to their island's food.

• An adaptation is a trait that helps an organism survive and reproduce.

• This gradual change in a species over many generations is called evolution.

• He realized that populations of organisms evolve, not individual organisms.

Multiple Choice

What is the definition of evolution?

• The process of an individual organism changing to fit its environment.

• The gradual change in a species or population over many generations.

• A trait that helps a single organism survive and reproduce.

• The way an organism's beak is shaped to find a specific food.

Multiple Choice

Based on Darwin's observations, what is the relationship between a finch's beak shape and its environment?

• All finches have the same beak shape, regardless of the environment.

• The environment causes an individual finch's beak to change shape over its life.

• Beak shape is an adaptation to the specific food available in the environment.

• A finch's beak shape determines the climate of the island.

Multiple Choice

A population of finches with varied beak shapes lives on an island. If a disease suddenly wiped out all plants with small, soft seeds, leaving only plants with large, hard nuts, what would most likely happen to the finch population over many generations?

• Individual finches would grow stronger beaks to crack the nuts.

• Finches with naturally stronger beaks would be more likely to survive and pass on that trait.

• The finches would migrate to a new island with different food.

• The entire finch population would quickly die out from starvation.

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The Theory of Natural Selection

• Species have descended with changes from other species over time.

• Different species are derived from common ancestors through common descent.

• Individuals better adapted to their environment are more likely to survive.

• Fitness is the measure of an individual's hereditary contribution to the next generation.

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Multiple Choice

Which statement best describes the theory of natural selection?

• Species are designed perfectly and do not change over time.

• Individuals better adapted to their environment are more likely to survive.

• An individual can change its traits during its lifetime to survive.

• All individuals in a species have an equal chance of survival.

Multiple Choice

What does the term 'fitness' refer to in the context of evolution?

• The physical strength and speed of an individual.

• The ability of an individual to find the most food.

• The length of an individual's life.

• An individual's hereditary contribution to the next generation.

Multiple Choice

Based on the principles of common descent and natural selection, what is the most likely relationship between two different species that share many similar traits?

• They are not related and the similarities are a coincidence.

• They are derived from a shared common ancestor.

• One species evolved from the other one directly.

• They live in the same environment but are unrelated.

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The Four Factors of Natural Selection

• Species tends to produce more offspring than can survive and reproduce.

• Individuals within a species show natural differences, also known as genetic variations.

• Offspring must compete for limited resources like food, water, and shelter.

• Helpful variations increase an individual's chances of surviving and reproducing to pass on traits.

Multiple Choice

What is the main result of the process of natural selection?

• The amount of available resources in an environment increases.

• Helpful traits are more likely to be passed on to the next generation.

• Individuals within a species learn to stop competing for food.

• All offspring born in a species will survive and reproduce.

Multiple Choice

Why must individual offspring within a species compete for resources?

• Helpful variations are passed on only to the strongest offspring.

• All species naturally try to claim the most territory.

• Some individuals have genetic variations while others do not.

• More young are produced than can survive with the limited resources available.

Multiple Choice

What would most likely happen in a species if all individuals were genetically identical and had no variations?

• Competition for resources like food, water, and shelter would end.

• The species would be better able to survive and reproduce.

• The species would stop producing more young than can survive.

• The species would be less able to survive changes in the environment.

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Speciation and Artificial Selection

Natural Selection

• Natural selection can lead to the formation of new species through a process called speciation.

• This occurs when a group separates and develops unique traits to survive in a new environment.

• These changes can result in a new plant or animal species that is distinct from the original.

Artificial Selection

• Artificial selection, or selective breeding, is a process where humans control which organisms reproduce.

• Humans choose specific desired traits, such as feather type, to pass on to the next generation.

• This method created diverse pigeon breeds that look very different from their wild ancestors.

Multiple Choice

What is the result of speciation?

• Humans choosing which organisms get to reproduce.

• An organism learning a new behavior.

• A group of organisms moving to a new location.

• The formation of a new and distinct species.

Multiple Choice

What is the key difference between natural selection leading to speciation and artificial selection?

• Natural selection happens in plants, while artificial selection happens in animals.

• Natural selection results in new traits, while artificial selection does not.

• Natural selection is a fast process, while artificial selection is a very slow process.

• Natural selection is driven by environmental pressures, while artificial selection is guided by human choices.

Multiple Choice

A dog breeder wants to create a new line of dogs that are excellent swimmers. Based on the principles of selection, what is the most effective method?

• Separate the dogs into two groups and see which group learns to swim faster.

• Train all of their dogs to swim every day.

• Allow only the dogs that are naturally the strongest swimmers to reproduce.

• Hope that a new species of swimming dog appears naturally over time.

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Types of Speciation

With Geographic Barriers

• A species is divided into two groups by a physical barrier.

• Isolated groups evolve differently because they can no longer interbreed with each other.

• A small group can also break off from the main group.

Without Physical Barriers

• A species is spread over a large area without a physical barrier.

• A new species can arise even if members live in the same area.

• This can happen if a subgroup uses a new food source or habitat.

Multiple Choice

What is the key difference between the two types of speciation described?

• One happens quickly and the other happens slowly over time.

• One involves new food sources and the other does not.

• One happens to a small group and one happens to a large group.

• One is caused by a physical barrier and one is not.

Multiple Choice

How can a new species develop even if the population is spread out in the same large area?

• The members of the species can no longer find each other to mate.

• A physical barrier, like a mountain, divides the population.

• A subgroup starts using a different habitat or food source.

• The entire species learns to eat a different kind of food together.

Multiple Choice

A single population of fish lives in a large lake. A new volcano erupts, dividing the lake into two smaller, separate lakes. What is the most likely long-term outcome for the fish populations?

• The two separated fish populations will evolve differently and may become two distinct species.

• The fish in one lake will go extinct, while the others survive.

• The fish in both lakes will remain a single species because they were once connected.

• The fish will find a way to cross the land barrier to continue interbreeding.

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Common Misconceptions

Misconception	Correction
Individuals can evolve during their lifetime.	Populations evolve over generations. Individuals cannot change their genes to adapt.
Evolution means organisms are always getting "better."	Evolution is adaptation to the current environment, not a path to perfection.
Humans evolved from monkeys.	Humans and monkeys share a common ancestor but evolved on different paths.

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Summary

• Charles Darwin developed the theory of evolution by natural selection.

• Evolution is the gradual change in inherited traits over many generations.

• Natural selection is driven by variation and the struggle for survival.

• Adaptations are traits that help an organism survive and reproduce.

• Speciation is the process that forms new and distinct species.

• Selection can be natural (by the environment) or artificial (by humans).

Poll

On a scale of 1-4, how confident are you about the concepts of evolution and natural selection?

• 1

• 2

• 3

• 4