Evidence for Evolution: Comparative Anatomy — Reading Comprehension

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MS-LS4-2
MS-LS4-3

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This middle school science reading passage explores the evidence for evolution through comparative anatomy, aligning with NGSS standards MS-LS4-2 and MS-LS4-3. Students will learn about homologous, analogous, and vestigial structures and how these concepts reveal evolutionary relationships between species. The passage begins with observable patterns in animal anatomy and moves into mechanistic explanations, using real-world examples like human, whale, and bat limbs, as well as bird and insect wings. It emphasizes scientific thinking, cause-and-effect relationships, and the importance of anatomical evidence in understanding evolution. Integrated glossary terms, a multiple-choice quiz, writing prompts, graphic organizers, and both English and Spanish versions ensure accessibility for diverse learners. The resource is audio-integrated and designed for grades 6-8, supporting comprehension and critical thinking about evolution.

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homologous-structures-1 — Homologous structures in different animals show similar bone patterns

Comparative anatomy is a branch of science that examines the similarities and differences in the body structures of different organisms. Scientists have discovered that certain patterns in animal anatomy can only be explained by evolutionary processes. For example, the bones in a human arm, a whale flipper, and a bat wing appear very different on the outside, but their internal structures are strikingly similar. This evidence helps scientists answer the fundamental question: How do we know that different species are related through evolution?

Homologous Structures: Evidence of Shared Ancestry
A homologous structure is a body part that has a similar structure but may serve a different function in different species. For instance, the arm bones in humans, the wings of bats, and the flippers of whales all share a similar arrangement of bones—such as the humerus, radius, and ulna. These similarities exist because these animals inherited these structures from a common ancestor. Even though these limbs are used for grasping, flying, or swimming, their underlying bone patterns reveal their shared origin. According to research, over 90% of vertebrate animals have limb bones arranged in this way. This pattern supports the idea that species change over time, adapting their limbs to new environments and ways of life.

Analogous and Vestigial Structures: Variations and Remnants
Not all similar-looking body parts are inherited from a common ancestor. Analogous structures are features that serve similar functions but have different internal structures and evolutionary origins. For example, the wings of birds and insects both help them fly, but their wing structures are built differently. Bird wings have bones, while insect wings are made of a thin membrane. These features evolved independently, showing how different species can develop similar solutions to environmental challenges—a process called convergent evolution.

Another important clue comes from vestigial structures. These are body parts that have lost most or all of their original function. For example, humans have an appendix, which is a small, unused pouch in the digestive system, and whales have tiny hip bones, even though they have no back legs. Ostriches, which cannot fly, still have small wings. These structures are leftovers from ancestors that used them more fully, and their presence is best explained by evolution.

The Big Picture: Why Comparative Anatomy Matters
Comparative anatomy connects to many scientific principles, including natural selection and adaptation. By analyzing anatomical patterns, scientists can build family trees (phylogenies) that show how species are related. This helps researchers understand how living things respond to environmental pressures and change over millions of years. Comparative anatomy also has real-world applications, such as improving medical research. For example, understanding the similarities between human and animal anatomy helps doctors develop new treatments and drugs by testing them in animals first.

Comparative anatomy reveals the deep connections among living things. By studying homologous, analogous, and vestigial structures, scientists can trace the history of life on Earth and explain the diversity of species we see today.

Interesting Fact:
Whale hip bones, once thought to be useless, actually help support reproductive organs, showing how vestigial structures can sometimes develop new functions!

What is the main purpose of comparative anatomy in science?

To study similarities and differences in body structures to understand evolutionary relationshipsTo compare animal behaviors in different environmentsTo identify new animal species in the wildTo explain how animals use their organs to survive

Which of the following is an example of a homologous structure?

The arm bones in humans and the wings of batsThe wings of birds and the wings of insectsThe beak of a bird and the mouth of a fishThe gills of a fish and the lungs of a mammal

What does the presence of vestigial structures in animals suggest?

That species have changed over time and some body parts are no longer neededThat all animals use every body part equallyThat vestigial structures have always been uselessThat animals do not share any common ancestry

What does 'convergent evolution' mean as used in the passage?

Unrelated species develop similar traits due to similar environmentsSpecies evolve from a common ancestorAnimals lose their body parts over timeAll animals become more alike as they age

In the passage, what does the word 'phylogeny' refer to?

The evolutionary history and relationships among speciesThe physical strength of an animalThe feeding habits of animalsThe migration patterns of birds

Why do bird wings and insect wings look similar but have different internal structures?

They evolved similar features to solve the same problem independentlyThey both inherited wings from a common ancestorBirds and insects have the same bonesThey live in the same habitats and eat the same food

How does comparative anatomy help in medical research, as mentioned in the passage?

By showing which animals are similar to humans so doctors can test treatmentsBy identifying which animals are the strongestBy discovering new animal species for studyBy teaching animals how to use human medicine

True or False: All similar-looking body parts in animals come from a common ancestor.

TrueFalse

True or False: Vestigial structures are completely useless in modern animals.

TrueFalse

What percentage of vertebrate animals have their limb bones arranged in a similar way, as stated in the passage?

Over 90%About 50%Less than 10%None