The Theory of Evolution by Natural Selection

The Theory of Evolution by Natural Selection

Middle School

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Learning Objectives

• Define genetic variations and explain how they arise in a population.

• Describe the key principles of natural selection as proposed by Charles Darwin.

• Classify the three main types of adaptations: structural, behavioral, and functional.

• Explain how advantageous traits become more common in a population over time.

Key Vocabulary

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Variation

Variation refers to the slight differences in inherited traits that exist among individuals within a population.

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Natural Selection

This is the process where better-adapted individuals are more likely to survive and reproduce successfully.

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Adaptation

An adaptation is a specific inherited trait that improves an organism's chances of surviving and reproducing.

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Structural Adaptation

These are physical features of an organism like its specific color, shape, or unique body parts.

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Behavioral Adaptation

This describes the particular way an organism acts or behaves in order to ensure its survival.

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Functional Adaptation

These adaptations are internal body processes that involve changes in the organism's biochemistry to survive.

Key Vocabulary

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Camouflage

An adaptation that allows a species to blend in with its environment, helping it to hide.

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Mimicry

This is an adaptation where one species evolves to resemble another species for protection or other advantages.

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Trait Distribution

This describes how often different traits, or characteristics, appear in a population of a particular species.

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Probability

In evolution, this is the mathematical likelihood a specific trait will help an organism survive and reproduce.

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Common Ancestor

This is an ancestor species from which two or more different, more recent species have since evolved.

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Genetic Mutation

A random change that occurs in the DNA of a cell, which can create new traits.

What are Genetic Variations?

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Advantageous Variations

• A beneficial trait increases the probability that an organism will survive.

• This helps organisms live longer and successfully reproduce in their specific environment.

• For example, green coloring helps an insect camouflage from predators on leaves.

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Disadvantageous Variations

• A harmful trait decreases the probability that an organism will survive.

• This makes it more difficult for organisms to live and reproduce.

• For instance, a yellow insect on a green leaf is easily seen.

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Neutral Variations

• A neutral trait does not have an observable effect on the organism.

• It neither helps nor harms the organism’s chances of survival or reproduction.

• For example, different fur colors in dogs of the same species.

Multiple Choice

What is the role of genetic variations in an organism's life?

• They can increase, decrease, or have no effect on an organism's ability to survive and reproduce.

• They only create traits that are harmful to an organism's survival.

• They only create traits that are beneficial to an organism's survival.

• They change the environment to better suit the organism.

Multiple Choice

What is the primary difference between an advantageous and a disadvantageous genetic variation?

• An advantageous variation increases survival probability, while a disadvantageous one decreases it.

• An advantageous variation is about color, while a disadvantageous one is about size.

• An advantageous variation makes reproduction harder, while a disadvantageous one makes it easier.

• An advantageous variation has no effect, while a disadvantageous one is always harmful.

Multiple Choice

A population of green insects lives on green leaves, but some are born yellow due to a genetic variation. If a plant disease caused all the leaves to turn yellow, what would be the most likely consequence for the yellow insects?

• The yellow insect's trait would become advantageous, making it harder for predators to see.

• The yellow insect's trait would remain disadvantageous, making it easier to see.

• The yellow insect's trait would become neutral because the leaf color no longer matters.

• The green insect's trait would become even more advantageous.

Darwin's Journey and Observations

• Charles Darwin developed his theory of evolution in the mid-1800s.

• His voyage to the Galápagos Islands was crucial for his work.

• He saw that tortoises on different islands had unique traits.

Multiple Choice

Who developed the theory of evolution in the mid-1800s?

• Charles Darwin

• Isaac Newton

• Albert Einstein

• Galileo Galilei

Multiple Choice

What was the significance of the Galápagos Islands to Darwin's work?

• It was a critical location for the observations that led to his theory.

• It was the place where he was born and raised.

• It was the only place in the world with tortoises.

• It was where he published his famous book.

Multiple Choice

What conclusion could Darwin draw from observing that tortoises on different islands had unique traits?

• That animals on different islands could develop unique traits based on their environment.

• That all tortoises in the world are genetically identical.

• That tortoises on different islands regularly swam between them.

• That the islands must have all been connected by land in the past.

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The Theory of Natural Selection

• More offspring are born than can survive, inheriting various traits from parents.

• Offspring show random genetic variations, making each individual unique.

• Individuals with advantageous traits are more likely to survive competition for resources.

• Helpful traits are passed on, increasing their proportion in the population.

Multiple Choice

Which statement best describes the theory of natural selection?

• Individuals with advantageous traits are more likely to survive and pass them on.

• All offspring born will survive and reproduce equally.

• Offspring can choose the traits they inherit from their parents.

• Genetic variations are caused by competition for resources.

Multiple Choice

What is the role of random genetic variation in the process of natural selection?

• It ensures that all offspring are identical to their parents.

• It is a direct result of competition for limited resources.

• It provides the variety of traits upon which natural selection can act.

• It guarantees that more offspring will survive than the environment can support.

Multiple Choice

Given that more offspring are born than can survive, what is the most likely long-term consequence for a population if its environment changes?

• The entire population would quickly develop new traits to survive.

• The proportion of individuals with traits suited for the new conditions would increase over time.

• The population would remain unchanged regardless of the environment.

• All individuals in the population would migrate to a different environment.

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Natural Selection and Trait Distribution

• Natural selection changes the traits of a whole population over many generations.

• It works on the probability of which individuals will survive and reproduce.

• Traits that help survival and reproduction become more common in a population.

• Traits that are harmful or disadvantageous for survival will become less common.

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Multiple Choice

What is the primary outcome of natural selection over many generations?

• The traits of a population change

• Individual animals decide to change their traits

• The environment of the population gets bigger

• All harmful traits disappear in one generation

Multiple Choice

Why do certain traits become more common within a population over time?

• Because they are the newest traits to appear

• Because they are passed down from a single parent

• Because they improve the chances of survival and reproduction

• Because they make an individual larger than others

Multiple Choice

If a new trait appears in a population that makes it harder for individuals to find food, what is the most likely prediction for the population over many generations?

• The harmful trait will be passed on to all offspring.

• The frequency of the harmful trait will decrease in the population.

• The entire population will disappear in one generation.

• The trait will become helpful to the population over time.

Types of Adaptations

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Structural Adaptations

• ​These are physical features an organism has to help it survive.

• ​​This includes a tortoise's shell or a chameleon's camouflage.

• ​These traits are inherited and passed down through generations.

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Behavioral Adaptations

• ​These are actions or behaviors that help an organism to survive.

• ​​Animals migrating to a warmer climate is one such example.

• ​Hunting in a pack is another key behavioral adaptation strategy.

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Functional Adaptations

• ​These are internal body processes that affect its biochemistry.

• ​​A snake producing venom for defense is a functional adaptation.

• ​A plant performing photosynthesis to create its own food is one.

Multiple Choice

What is a structural adaptation?

• A physical feature an organism has

• An action or behavior an organism does

• An internal process that an organism's body performs

• A place where an organism finds food

Multiple Choice

How does a behavioral adaptation, such as migrating, differ from a functional adaptation, such as producing venom?

• Behavioral adaptations are actions, while functional adaptations are internal processes.

• Behavioral adaptations are physical features, while functional adaptations are actions.

• Behavioral adaptations are inherited, while functional adaptations are not.

• Behavioral adaptations relate to defense, while functional adaptations relate to biochemistry.

Multiple Choice

An arctic fox has a thick coat of fur for warmth and hunts at night. Which statement correctly classifies these two adaptations?

• The thick fur is a structural adaptation, and hunting at night is a behavioral adaptation.

• The thick fur is a functional adaptation, and hunting at night is a structural adaptation.

• Both the fur and the hunting behavior are examples of structural adaptations.

• Both the fur and the hunting behavior are examples of functional adaptations.

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Adaptations

Camouflage

• Camouflage is a structural adaptation allowing a species to blend in with its surroundings.

• This adaptation helps organisms avoid being seen by predators, increasing their chances of survival.

• Rapid environmental changes can make camouflage ineffective, threatening the species’ long-term survival.

Mimicry

• Mimicry is an adaptation where one species evolves to look or act like another species.

• This tactic helps a harmless species appear more dangerous, providing it with great protection.

• This increases the probability of survival and reproduction for the individuals that possess it.

Multiple Choice

What is the primary purpose of adaptations like camouflage and mimicry?

• To increase the chances of survival and reproduction

• To allow a species to change its environment

• To make a species more intelligent over time

• To help different species communicate with each other

Multiple Choice

How does mimicry differ from camouflage as a survival strategy?

• Mimicry involves a species looking like another species, while camouflage involves a species blending in with its surroundings.

• Camouflage is an adaptation to avoid predators, while mimicry is an adaptation to attract prey.

• Mimicry is a short-term tactic for protection, while camouflage is a long-term survival strategy.

• Camouflage involves changing behavior, while mimicry involves changing appearance.

Multiple Choice

A species of lizard has coloration that allows it to be camouflaged in a sandy desert. If a sudden climate shift leads to widespread vegetation growth in the area, what is the most likely outcome for this lizard species?

• The species' camouflage would become ineffective, threatening its long-term survival.

• The species would immediately evolve a new color to match the new environment.

• The species' predators would no longer be able to see them.

• The species would switch to mimicry and copy a more dangerous animal.

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Common Misconceptions

Misconception	Correction
Individual organisms can choose to adapt.	Adaptation is not a choice; it happens to populations over generations.
Individuals evolve.	Populations evolve over time, not individual organisms.
Evolution is 'just a theory.'	In science, a theory is a well-supported explanation for natural phenomena.
All mutations are harmful.	Mutations can be harmful, neutral, or beneficial.

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Summary

• Genetic variations are random and provide the raw material for natural selection.

• Natural selection makes advantageous traits more common in a population over generations.

• An adaptation is a heritable trait that increases an organism's chances of survival.

• Rapid environmental change can lead to extinction if a population cannot adapt.

Poll

On a scale of 1-4, how confident are you about explaining how natural selection leads to changes in a population?

• 1

• 2

• 3

• 4