Natural Selection and Change Over Time

Natural Selection and Change Over Time

Middle School

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Learning Objectives

• Describe how natural selection changes the distribution of traits in a population over time.

• Explain how genetic variation increases a population's chances of survival and reproduction.

• Analyze fossil record data to identify patterns in the history of life.

• Use anatomical and molecular evidence to reconstruct evolutionary history and infer lines of descent.

• Explain how mathematical models represent the effects of natural selection on population traits.

Key Vocabulary

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Evolution

Evolution is the process of change in a species that occurs over many, many generations.

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Variation

Variation refers to the natural differences that exist between any individuals of the same species.

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Adaptation

An adaptation is an inherited trait that helps an organism better survive and reproduce in its environment.

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Natural Selection

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

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Fitness

Fitness in biology measures how well an organism can survive and reproduce in its environment.

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Fossil

A fossil represents the preserved remains, impressions, or traces of an organism that lived long ago.

Key Vocabulary

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Mutation

A mutation is a random change that occurs in the genetic material of an organism.

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Homologous Structure

Similar structures inherited from a common ancestor that may have different functions in different species.

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Trait Distribution

This refers to the pattern of how frequently different traits or characteristics appear in a population.

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Probability

This is the mathematical measure of the chance that a particular event, like inheriting a trait, will occur.

Early Ideas About Evolution

• Lamarck proposed that species change in small, gradual steps over time.

• Lyell showed Earth was old enough for gradual evolution to occur.

• Anning’s fossil discoveries provided evidence that species could become extinct.

Multiple Choice

What did Lamarck propose about how species change over time?

• They change in small, gradual steps.

• They never change at all.

• They change suddenly in large leaps.

• They only change when they become extinct.

Multiple Choice

How did the work of geologist Charles Lyell support the idea that species change gradually?

• It showed that Earth was old enough for these slow changes to occur.

• It proved that fossils were evidence of past life.

• It suggested that Earth's features were created all at once.

• It provided a list of all species that had ever lived.

Multiple Choice

When considered together, what do the contributions of Lamarck, Lyell, and Anning suggest about the history of life?

• Life on Earth has a long history of gradual change, and some species have disappeared over time.

• Species do not change, but they can become extinct.

• The Earth is very old, but this has not affected the development of species.

• Fossil discoveries are the main cause of gradual evolution.

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Darwin's Journey and Key Observations

• On the HMS Beagle, Darwin saw amazing biodiversity and fossils of extinct animals.

• ​On the Galápagos Islands, finches had unique beaks for different food sources.

• These unique beak shapes were adaptations that helped the finches survive and reproduce.

• Darwin concluded species change over generations to adapt to their new conditions.

Multiple Choice

What was the primary conclusion Darwin reached based on his observations of life's diversity and the fossil record?

• Species change over many generations to adapt to their environment.

• The diversity of life has been decreasing over time.

• Fossils are the remains of animals that no longer exist.

• All finches on the Galápagos Islands had identical beaks.

Multiple Choice

What is the significance of the different beak shapes Darwin observed in the Galápagos finches?

• They are specialized traits that help the finches survive by eating different types of food.

• They are decorative features used to attract mates from other islands.

• They are temporary changes that occur within a single finch's lifetime.

• They are random variations that provide no specific advantage for survival.

Multiple Choice

Based on Darwin's conclusions, what would be the most likely outcome if a new type of insect became the main food source on one of the Galápagos Islands?

• Finches with beaks adapted for the new food source would be more likely to survive and pass on their traits.

• All the finches would immediately grow new beaks to eat the new food.

• The finches would migrate to another island with their old food source.

• The finch population would remain unchanged regardless of the food supply.

The Mechanism of Natural Selection

• Inherited traits interact with the environment, influencing survival and reproduction.

• The process depends on overproduction, variation, and competition for resources.

• Favorable traits become more common in the population over many generations.

Multiple Choice

Which statement best defines the mechanism of natural selection?

• A process where favorable traits become more common in a population over many generations.

• A process where an individual animal can choose to change its traits.

• A process that allows individuals to adapt to the environment in their lifetime.

• A process that only occurs when there are unlimited resources for all.

Multiple Choice

What is the relationship between overproduction, variation, and competition in an ecosystem?

• They are the necessary components for natural selection to take place.

• They are the final results of the natural selection process.

• They prevent inherited traits from changing over time.

• They ensure that all individuals in a population are identical.

Multiple Choice

If a new predator enters an environment, how will this most likely affect a prey population with inherited variations for camouflage?

• The trait for better camouflage will likely become more common in the population over time.

• The entire population will immediately develop better camouflage.

• The environment will change to reduce the number of predators.

• The animals without the trait will learn to find new food sources.

Mutations

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Beneficial Mutations

• ​These mutations increase an organism's ability to survive and reproduce.

• ​​This is often referred to as an increase in fitness.

• ​An example is a beetle that can better resist pesticides.

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Harmful Mutations

• ​These mutations decrease an organism's ability to survive and reproduce.

• ​​This is often referred to as a decrease in fitness.

• ​Cystic fibrosis is an example of a harmful genetic mutation.

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Neutral Mutations

• ​These mutations do not have an observable effect on the organism.

• ​​They do not affect an organism's chances of survival or reproduction.

• ​An example is having a widow's peak hairline, red hair, hetereochromia, etc. in humans.

Multiple Choice

What is the primary effect of a beneficial mutation?

• It increases an organism's ability to survive and reproduce.

• It has no observable effect on the organism.

• It changes an organism's appearance but not its survival.

• It decreases an organism's ability to find a mate.

Multiple Choice

How does a harmful mutation's effect on an organism differ from a neutral mutation's effect?

• A harmful mutation decreases fitness, while a neutral mutation has no effect.

• A harmful mutation is caused by the environment, while a neutral mutation is not.

• A harmful mutation affects reproduction, while a neutral mutation only affects survival.

• A harmful mutation is always visible, while a neutral mutation is not.

Multiple Choice

A large population of beetles has lived in a farmer's field for many years. The farmer begins using a new pesticide to protect the crops. Which genetic change would be most likely to increase in the beetle population over time?

• A mutation that allows a beetle to better resist the pesticide.

• A mutation that results in a widow's peak hairline.

• A mutation that changes the beetle's color to be brighter.

• A mutation that slightly reduces the beetle's size.

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Evidence from the Fossil Record

• The fossil record is the chronological collection of all known fossils.

• Fossils are found in layers of sedimentary rock, with deeper layers being older.

• It documents the existence, diversity, and extinction of various life forms.

• This record reveals major evolutionary changes and new anatomical features over time.

Multiple Choice

What is the fossil record?

• The collection of fossils arranged in chronological order.

• A record of all rocks found within Earth's crust.

• A list of every species currently living on Earth.

• The study of how sedimentary rocks are formed.

Multiple Choice

How does the arrangement of fossils in rock layers provide evidence of evolution?

• Deeper rock layers contain older fossils, showing how life has changed.

• All rock layers contain the same types of fossils.

• The age of a fossil is determined by its size, not its location.

• Only igneous rock contains fossils that show changes in life.

Multiple Choice

If paleontologists consistently find fossils of simple organisms in deep rock layers and more complex organisms in shallower layers, what is the most logical conclusion?

• The organisms found in shallow layers are the ancestors of those in deep layers.

• Major evolutionary changes have occurred over geologic time.

• The rock layers have been overturned by geological events.

• All life forms appeared on Earth at the same time.

Anatomical and Embryological Evidence

• Homologous structures are similar structures inherited from a common ancestor.

• Early embryos of different vertebrates show remarkable similarities.

• These similarities help reconstruct the evolutionary history of organisms.

Multiple Choice

What is the definition of homologous structures?

• Similar structures inherited from a common ancestor

• Structures that have the exact same function in different species

• Structures that only appear in the embryonic stage of an organism

• Structures that have been lost over the course of evolution

Multiple Choice

What is the scientific importance of early embryos of different vertebrates showing remarkable similarities?

• They prove that the adult forms of all vertebrates are identical

• They show that all vertebrates live in the same type of environment

• They provide evidence for a shared evolutionary history

• They indicate that all vertebrate embryos grow at the same rate

Multiple Choice

Scientists observe that a human arm, a whale flipper, and a bat wing have a very similar underlying bone structure, even though they are used for different functions. What is the best conclusion that can be drawn from this observation?

• The organisms live in the same habitat

• The organisms likely share a common ancestor

• All three organisms evolved from a species that could fly

• The similarity in structure is purely a coincidence

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Modern Genetic and Molecular Evidence

DNA Comparison

• All known life uses DNA as its genetic material, pointing to a common ancestor.

• Scientists can directly compare the DNA sequences of different species.

• The more similar the DNA sequences are, the more closely related the species are.

Protein Comparison

• Genes contain the code for making specific proteins.

• By comparing amino acid sequences in a protein, scientists find evolutionary links.

• Fewer differences in the amino acid sequence mean a closer relationship.

Multiple Choice

What fundamental conclusion can be drawn by comparing the DNA or protein sequences of different organisms?

• How closely related different species are

• The exact age of a fossil

• Which habitats organisms prefer to live in

• How organisms reproduce

Multiple Choice

What is the relationship between the genetic information in DNA and the structure of proteins?

• The DNA sequence determines the amino acid sequence in proteins.

• Proteins are a more reliable source of evidence than DNA.

• All living things produce the exact same proteins.

• Amino acids are the building blocks of DNA.

Multiple Choice

A scientist compares a specific protein from three different species. The protein from Species A has 5 amino acid differences from Species B, and 28 differences from Species C. Which conclusion is best supported by this data?

• Species A and B are the most closely related.

• Species A and C are the most closely related.

• Species B and C are the most closely related.

• All three species are equally related.

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Modeling Changes in Trait Distribution

• Scientists use mathematical models to show how traits in a population change.

• For example, large beaks are an advantage when only hard seeds are available.

• A graph shows large-beaked birds increasing and small-beaked birds decreasing over time.

• This data shows that natural selection causes adaptation in a population.

Multiple Choice

What is the primary purpose of using mathematical models in the study of population traits?

• To show how traits within a population change over time.

• To count the exact number of individuals in a population.

• To prove that all birds have the same beak size.

• To prevent any changes in the food supply for animals.

Multiple Choice

Based on the example of bird beaks, what is the relationship between a change in food availability and the traits of a population?

• A change in food can give a survival advantage to birds with certain beak sizes.

• The beak size of a bird determines what food will be available.

• All birds will develop larger beaks when food changes.

• Changes in food availability do not affect bird beak size.

Multiple Choice

A graph of a bird population shows that, over time, the number of small-beaked birds increases while the number of large-beaked birds decreases. What is the most likely cause of this observed trend?

• The primary food source became more accessible to birds with smaller beaks.

• The birds with larger beaks decided to migrate to a new area.

• The overall bird population grew larger, including all beak sizes.

• The environment remained stable with no changes to the food supply.

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Common Misconceptions

Misconception	Correction
Individuals evolve during their lifetime.	Populations evolve over generations, not individuals.
Evolution means organisms are always getting "better."	Fitness depends on the environment, not on being "better."
All mutations are harmful.	Mutations can be harmful, neutral, or even beneficial.
Organisms evolve on purpose.	Evolution happens through random variation, not by trying.

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Summary

• Natural selection causes traits that aid survival to become more common over time.

• The ultimate source of all new traits is random genetic mutation.

• Evidence for evolution comes from fossils, anatomical similarities, embryology, and molecular data.

• The fossil record shows life's history, while math models track trait changes.

Poll

On a scale of 1-4, how confident are you in your ability to explain how natural selection leads to change in a population?

• 1

• 2

• 3

• 4