Understanding Biological Evolution and Diversity — Reading Comprehension

Grades

Standards

RI.3.3
RI.4.3
RI.5.3
3-LS4-2

About This Reader

This passage addresses the NGSS standard 3-LS4-2 focusing on biological evolution and the unity and diversity of life. The content explains how evolution occurs over millions of years as organisms adapt to their environments. It discusses extinct species like dinosaurs and woolly mammoths, and explains how scientists use fossils to understand changes in organisms over time. The passage provides concrete examples such as horse evolution from small multi-toed ancestors to larger hooved animals in response to changing environments like expanding grasslands. Students will learn about the connections between modern organisms and their ancestors, understanding both the unity (shared ancestry) and diversity (different adaptations) that characterize life on Earth. The material is presented at an appropriate reading level for upper elementary students with clear examples that help visualize abstract evolutionary concepts. The passage supports learning objectives related to understanding that some animals that once lived on Earth are no longer found anywhere and that fossils provide evidence about organisms and environments from long ago.

CONTENT PREVIEW

When we look at the amazing variety of plants and animals on Earth today, we're seeing the results of a process called evolution. Evolution happens over very long periods of time—millions of years!—as living things change to better survive in their environments.

If we could travel back in time, we would see that many animals and plants looked different from those alive today. Some creatures that once lived on Earth, like dinosaurs and woolly mammoths, have disappeared completely—they became extinct when they couldn't adapt to changing environments.

How do we know this? Scientists find clues in fossils—the preserved remains of ancient organisms. By studying fossils in different rock layers, scientists can see how living things have changed over time. Sometimes, they find fossils of organisms that had features similar to modern animals but also important differences.

For example, horse fossils show that ancient horses were much smaller (about the size of a dog!) and had multiple toes instead of hooves. Over millions of years, as grasslands spread and the environment changed, horses evolved to become larger, faster, and developed hooves that were better for running on hard ground.

Even though living things look different from their ancestors, they share a unity—connections that show they're related. Just like you might have your grandmother's eyes or your father's smile, organisms share traits with their ancestors while developing new features that help them survive in their environments. This combination of shared ancestry (unity) and different adaptations (diversity) is what makes the story of life on Earth so fascinating!

According to the passage, evolution happens over:

hundreds of yearsthousands of yearsmillions of yearsbillions of years

What does the passage say happened to dinosaurs and woolly mammoths?

They migrated to different continentsThey became extinctThey evolved into modern animalsThey hibernated underground

What evidence do scientists use to learn about organisms that lived long ago?

Ancient books and writingsFossilsMicroscopic examination of living animalsDNA testing of modern animals

Ancient horses were different from modern horses because they:

were much larger than modern horseswere about the size of a dog and had multiple toescould fly short distanceslived in the ocean

According to the passage, why did horses evolve to have hooves?

To look more attractive to other horsesBecause horses with hooves were kept as petsTo be better at running on hard groundTo dig for food more efficiently

The passage suggests that organisms alive today:

are completely different from ancient organismsare exactly the same as ancient organismsshare some traits with ancient organisms but have new featurescan transform into their ancestors

The term "unity" in the passage refers to:

all organisms looking exactly the sameorganisms working together to surviveconnections that show organisms are relatedanimals living in the same habitat

What environmental change does the passage mention that influenced horse evolution?

The spread of grasslandsThe rise of mountain rangesThe formation of deep oceansThe increase in global temperature