Evidence of Evolution

Evidence of Evolution

Middle School

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Learning Objectives

• Define the five main categories of evidence for evolution.

• Explain how each type of evidence supports evolution by natural selection.

• Distinguish between homologous and analogous structures to understand evolution.

• Analyze data to infer the evolutionary relationships between different species.

Key Vocabulary

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Evolution

The process of change in the inherited traits of biological populations over many successive generations.

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Natural Selection

Organisms better adapted to their environment are more likely to survive and produce more offspring.

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Comparative Anatomy

The study of similarities and differences in the anatomy of different species to understand evolution.

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Homologous Structure

A similar structure in related organisms because it was inherited from a common shared ancestor.

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Analogous Structure

A structure similar in function in unrelated organisms but with a different evolutionary origin.

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Vestigial Structure

A structure in an organism that has lost all or most of its original function.

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Darwin's Theory and Natural Selection

• Darwin's Galápagos voyage led to his groundbreaking theory of evolution.

• Organisms evolve over time through a process called natural selection.

• An organism's fitness is its ability to survive and reproduce.

• Helpful traits increase in a population over generations, not in an individual.

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Multiple Choice

According to the principle of natural selection, which organisms are most likely to survive and reproduce?

• Organisms that are best adapted to the environment.

• Organisms that can change their traits during their lifetime.

• The largest and strongest organisms in a population.

• Organisms that produce the highest number of offspring, regardless of their traits.

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Evidence for Evolution: The Fossil Record

• Fossils are preserved remains showing the history of life on Earth as evidence for evolution.

• Simpler organisms are found in older, deeper rock layers, a rule called superposition.

• The fossil record shows whales evolved from land-dwelling creatures over millions of years.

• Scientists use relative dating (position) and absolute dating (radioactive decay) to find fossil ages.

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Multiple Choice

According to the Law of Superposition, where would you expect to find the oldest fossils?

• In the deepest, undisturbed rock layers.

• In the top, most recent rock layers.

• Only in igneous rock formations.

• Scattered randomly through all rock layers.

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Comparative Anatomy

Homologous Structures

• These are structures in different species that are similar because they share a common ancestor.

• While their functions may differ, their underlying internal structure and development are the same.

• The forelimbs of humans, whales, and bats are examples of homologous structures.

Analogous Structures

• These structures have a similar function but did not evolve from a common ancestor.

• They evolved independently in species living in similar environments or facing similar challenges.

• The wings of a bird and the wings of an insect are both used for flight.

Multiple Choice

The wing of a bat and the flipper of a whale are considered homologous structures. What does this suggest about their evolutionary relationship?

• They share a common ancestor.

• They evolved independently to have similar functions.

• Bats evolved from whales.

• They live in the same type of environment.

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Embryology and Vestigial Structures

Comparative Embryology

• ​Comparative embryology is the study of how organisms develop before being born.

• ​​Many species look very similar in their early embryonic stages of development.

• ​Vertebrate embryos have gill slits and tails, which suggests a common ancestor.

Vestigial Structures

• ​A vestigial structure is a body part that has lost its original function.

• ​​These parts were useful to an ancestor but are no longer needed today.

• ​Examples include the human tailbone and small pelvic bones found inside some whales.

Multiple Choice

What does the presence of a vestigial structure, like the pelvic bones in a whale, suggest?

• The whale's ancestors likely lived on land.

• The structure will become functional in future generations.

• The whale is a very primitive organism.

• The structure has a hidden, unknown function.

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Biogeography and Molecular Evidence

Biogeography

• Biogeography is the study of where organisms live and why they are found there.

• Species living close to each other are more related than species in similar but distant habitats.

• Galápagos finches evolved different beaks to adapt to the various food sources on each island.

Molecular Evidence

• Molecular biology compares the DNA of different species to provide strong evidence for evolution.

• Organisms that are closely related have DNA sequences that are much more similar to each other.

• By comparing DNA, scientists can estimate when species diverged from a common ancestor.

Multiple Choice

Darwin's finches on the Galápagos Islands had different beak shapes. According to the concept of adaptive radiation, why did this occur?

• The finches evolved to best suit the different food sources available on each island.

• The finches on different islands were entirely different, unrelated species from the start.

• All the finches were trying to become one single, perfectly adapted species.

• The beak differences were random and provided no survival advantage.

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Common Misconceptions About Evolution

Misconception	Correction
Traits acquired during life are passed to offspring.	Only genetic traits are inherited, not traits acquired during life.
Individual organisms can evolve on their own.	Populations, not individuals, evolve over many generations.
Evolution is "just a theory," meaning it is a guess.	A scientific theory is a well-supported explanation based on evidence.
Evolution creates "perfect" organisms.	It favors organisms that are "fit enough" to survive and reproduce.

Multiple Choice

How does the evidence provided by homologous structures differ from the evidence provided by analogous structures in explaining evolutionary relationships?

• Homologous structures suggest a common ancestor, while analogous structures suggest convergent evolution.

• Homologous structures are about similar function, while analogous structures are about similar ancestry.

• Homologous structures prove that species live in similar environments, while analogous structures prove they do not.

• Homologous structures are only found in fossils, while analogous structures are found in living species.

Multiple Choice

A scientist unearths two fossils in undisturbed layers of rock. Fossil A is in a layer several feet below the layer containing Fossil B. What can the scientist conclude about their relative ages?

• Fossil A is older than Fossil B.

• Fossil B is older than Fossil A.

• Fossil A and Fossil B are approximately the same age.

• It is impossible to know without absolute dating.

Multiple Choice

If a species of bird that primarily eats small seeds is introduced to an island where the only available food is large, hard-shelled nuts, what is a likely long-term outcome according to the theory of evolution?

• Over generations, birds with naturally larger, stronger beaks will be more likely to survive and reproduce, leading to a population with larger beaks.

• All the birds will quickly learn to crack the hard nuts and pass this skill to their offspring.

• The individual birds will grow larger beaks during their lifetime to adapt to the new food source.

• The species will become extinct because it cannot adapt to the new environment.

Multiple Choice

Two species have very similar DNA sequences in a particular gene. What is the most logical conclusion that can be drawn from this evidence?

• These two species diverged from a common ancestor more recently than from species with more different DNA.

• These two species are not related to each other in any way.

• DNA similarity is a coincidence and does not provide evidence for evolution.

• One species evolved directly from the other.

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Summary

• The fossil record shows changes in species over time, ordered by age.

• Comparative anatomy reveals shared ancestry through homologous and analogous structures.

• Vestigial structures and embryology point to descent from common ancestors.

• Biogeography and molecular evidence from DNA confirm evolutionary relationships.

Poll

On a scale of 1-4, how confident are you about explaining the different types of evidence for evolution?

• 1

• 2

• 3

• 4