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Theory of Evolution — Reading Comprehension

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MS-LS4-1
MS-LS4-2

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This middle school science passage explains the theory of evolution and the concept of common ancestry, aligning with NGSS standards MS-LS4-1 and MS-LS4-2. Students will learn how biological evolution describes changes in species over generations, the evidence for a shared ancestry among all living things, and Charles Darwin’s contributions through his observations on the HMS Beagle. The passage clarifies the scientific meaning of 'theory,' discusses mechanisms like natural selection, and provides real-world examples, including Galápagos finches and antibiotic resistance. Designed for grades 6-8, the resource includes a glossary, Spanish translation, simplified version, comprehension quiz, writing prompts, and interactive graphic organizers. Audio integration supports accessibility, making it ideal for diverse classroom needs. Keywords: evolution, common ancestry, Darwin, adaptation, natural selection, NGSS.

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Theory of Evolution and Common Ancestry — Representation of human evolution

Biological evolution is the scientific explanation for how living things change across generations. Scientists observe that species are not fixed—over long periods, populations shift in characteristics, sometimes leading to entirely new species. This ongoing process helps explain the enormous diversity of life on Earth. Understanding evolution is essential to modern biology and helps us answer big questions, such as why different organisms share similar features or how new species arise.

How Evolution Works: Variation, Inheritance, and Natural Selection

Evolution relies on three main mechanisms: variation, inheritance, and natural selection. Variation means individuals within a species are not all identical. For example, some finches on the Galápagos Islands have large beaks, while others have small beaks. Inheritance allows traits to pass from parents to offspring through genes. Natural selection is the process where individuals with traits suited to their environment tend to survive and reproduce more successfully. Over many generations, advantageous traits become more common, causing the species to adapt.

Evidence for Common Ancestry: The Tree of Life

Scientists have collected evidence—such as fossils, DNA similarities, and shared body structures—to show that all life forms are related. This idea is called common ancestry. The “tree of life” is a model that shows how species branch out from shared roots, with each split representing a common ancestor. For example, humans and chimpanzees share about 98% of their DNA. The presence of vestigial structures, such as tiny leg bones in whales, also supports this idea.

Darwin’s Discovery and the Scientific Meaning of Theory

Charles Darwin’s voyage on the HMS Beagle was critical for the development of evolutionary theory. Observing finches and tortoises on the Galápagos Islands, Darwin noticed that their differences were related to the environments they inhabited. He proposed that species change over time through natural selection. In science, a theory is not just a guess, but a well-tested explanation supported by evidence. Evolution is both a fact—because we observe change—and a theory—because it explains the mechanisms causing change. Importantly, evolution does not mean progress toward perfection; it describes adaptation to current environments.

Evolutionary principles have real-world applications, such as understanding antibiotic resistance in bacteria or breeding crops for specific traits. These concepts connect to broader scientific principles, showing how all life is interconnected and constantly changing.

Interesting Fact:
Some bacteria can evolve resistance to antibiotics in as few as 11 days, demonstrating how quickly evolution can occur under strong selection pressure.

What does biological evolution explain?

How living things change over generationsHow rocks are formedWhy the weather changesHow stars are created

Which of the following is NOT a mechanism of evolution mentioned in the passage?

VariationPhotosynthesisInheritanceNatural selection

What evidence supports the idea of common ancestry?

Fossils, DNA similarities, and shared body structuresMoon phasesSound wavesGravity

According to the passage, what did Darwin observe on the Galápagos Islands?

Finches and tortoises with traits related to their environmentsVolcanoes eruptingFish migration patternsRainforest weather

What does the term 'theory' mean in science, according to the passage?

A well-tested explanation supported by evidenceA wild guessA story from the pastA set of laws

In the context of evolution, what is natural selection?

The process where individuals with helpful traits survive and reproduce more successfullyThe study of plantsA random eventThe movement of tectonic plates

Why is evolution important in understanding antibiotic resistance?

Because bacteria evolve quickly and can become resistant to medicinesBecause it explains plant growthBecause it predicts earthquakesBecause it creates new planets

According to the passage, evolution means species become perfect over time. (True/False)

TrueFalse

According to the passage, evolution only happens in animals. (True/False)

TrueFalse

Which percentage of DNA do humans and chimpanzees share, as stated in the passage?

About 98%25%45%100%