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Natural Selection: Nature’s Way of Choosing Traits — Reading Comprehension

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MS-LS3-2

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This NGSS-aligned science reading passage explains the concept of natural selection and how it drives the evolution of traits in living organisms. Students learn how genetic variations lead to differences in survival and reproduction, and how certain traits become more common over generations. The passage uses real-world examples like camouflage and Darwin’s finches to help students understand how environments shape populations. It contrasts natural selection with artificial selection and reinforces the idea that natural selection is a key mechanism of evolution. This resource supports MS-LS3-2 and builds science comprehension through engaging, age-appropriate text.

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Charles Darwin 01 — "Charles Darwin" by Julia Margaret Cameron / Wikimedia Commons.

Natural selection is the process by which organisms that are better adapted to their environment are more likely to survive and reproduce. Over time, their traits become more common in the population. This idea was first described by Charles Darwin and is one of the main ways evolution happens.

In every species, individuals are born with slight differences, or variations, in traits like color, size, or speed. These variations are caused by genetic differences and can be passed from parents to offspring. Some traits give an organism an advantage—such as helping it find food, avoid predators, or survive harsh conditions. When these individuals survive and reproduce, they pass those helpful traits to the next generation.

For example, in a forest, green-colored insects may be harder for birds to see. If birds eat more brown insects, the green ones survive longer and have more offspring. Over many generations, more of the insect population becomes green. This is natural selection at work: traits that help survival become more common.

Natural selection is different from artificial selection, where humans choose which traits to pass on. In natural selection, the environment does the “choosing.” It shapes the traits of populations over time, often leading to new species.

Understanding natural selection helps explain why living things are so well-suited to their habitats and why traits can change over generations.

Fun Fact: Darwin’s study of finches in the Galápagos Islands showed how their beak shapes evolved based on the type of food they ate—some for seeds, others for insects!

What is natural selection?

Humans choosing traitsPlants growing faster in sunNature favoring helpful traitsRandom changes in DNA

Who first described natural selection?

Gregor MendelIsaac NewtonCharles DarwinAlbert Einstein

What causes variation in traits?

Water and sunlightDNA differencesFood choicesSeasonal changes

Why do green insects survive better in a forest?

They fly fasterThey eat moreBirds can’t see them easilyThey change colors

What happens to helpful traits over time?

They disappearThey stay the sameThey become more commonThey move to other species

How is natural selection different from artificial selection?

It’s slowerTraits are chosen by nature, not humansIt uses no genesIt only affects plants

What is the main idea of the passage?

Natural selection causes traits to disappearThe environment shapes traits through survivalAll organisms change randomlyTraits are chosen by scientists

If a drought affects a plant species, which plants will likely survive?

The ones with large leavesThe ones needing lots of waterThe ones adapted to dry conditionsThe ones that grow near rivers