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The Theory of Evolution by Natural Selection
life sciencebiologyevolution
普通
Reading
The Theory of Evolution by Natural Selection
life sciencebiologyevolution
普通
Paragraph 1
The theory of evolution by natural selection, first comprehensively formulated by Charles Darwin in his 1859 book On the Origin of Species, is the foundational principle of all modern biology. It provides a rational, evidence-based explanation for the immense diversity of life on Earth and the remarkable ways in which organisms are adapted to their environments. The theory is built upon a few key observations and inferences. Darwin observed that organisms produce more offspring than can possibly survive, that there is variation among individuals within a species, and that these variations are heritable. From these observations, he inferred that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits on to the next generation.
Paragraph 2
The core mechanism of the theory is natural selection, often summarized as 'survival of the fittest.' However, this phrase can be misleading. 'Fitness' in a biological context does not refer to physical strength or health, but rather to an organism's reproductive success—its ability to pass its genes on. Natural selection is the process whereby environmental pressures—such as predation, climate, and competition for resources—'select' for certain heritable traits. For example, in a forest inhabited by sharp-eyed predators, brown beetles may survive and reproduce more effectively than bright green beetles because they are better camouflaged. Over generations, this differential survival and reproduction leads to an increase in the frequency of the brown coloration trait in the population.
Paragraph 3
For natural selection to operate, there must be variation within a population. Without variation, all individuals would be identical, and there would be no traits to select for. The ultimate source of all new genetic variation is random mutation—changes in the DNA sequence. While most mutations are neutral or harmful, occasionally a mutation arises that confers a survival or reproductive advantage. Sexual reproduction is another major source of variation, as it shuffles existing parental genes into new combinations in the offspring. This constant generation of new variations provides the raw material upon which natural selection can act, allowing populations to adapt to changing environmental conditions over time.
Paragraph 4
The evidence for evolution by natural selection is vast and comes from many different fields of science. The fossil record provides a clear history of life on Earth, showing the gradual changes in organisms over geological time and the emergence of new species from ancestral forms. Comparative anatomy reveals homologous structures—features like the pentadactyl (five-fingered) limb found in humans, bats, whales, and cats—which share a common underlying structure despite their different functions, pointing to a common ancestor. Biogeography, the study of the distribution of species, shows that closely related species are often found in close geographic proximity, supporting the idea that they diverged from a local ancestor. Finally, modern genetics and molecular biology provide the most direct evidence, allowing scientists to compare DNA sequences and demonstrate the precise genetic relationships between different species.
Paragraph 5
It is crucial to understand that evolution by natural selection is not a random process, nor does it have a predetermined goal. While the underlying source of variation (mutation) is random, the process of selection itself is non-random. It consistently favors traits that enhance reproductive success in a specific environment. Evolution does not strive to create 'perfect' organisms; it simply adapts populations to their current circumstances. A trait that is advantageous in one environment might be neutral or detrimental in another. The theory provides a powerful framework for understanding not only the history of life but also pressing contemporary issues, such as the evolution of antibiotic resistance in bacteria and the conservation of biodiversity in a rapidly changing world.
The word 'foundational' in paragraph 1 is closest in meaning to...
The word 'detrimental' in paragraph 5 is closest in meaning to...
According to paragraph 2, what is the biological definition of 'fitness'?
What can be inferred from the example of the brown and green beetles in paragraph 2?
According to paragraph 3, what is the ultimate source of all new genetic variation?
Why does the author mention homologous structures in paragraph 4?
What does the author imply about the process of natural selection in paragraph 5?
Which of the following is NOT listed in paragraph 4 as a source of evidence for evolution?
Look at the four squares [■] that indicate where the following sentence could be added to paragraph 2. Where would the sentence best fit?
This leads to adaptation, the process by which populations become better suited to their environment over time.
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The theory of evolution by natural selection explains that life's diversity is the result of organisms adapting to their environments over time.
Select 3 answer choices that express the most important ideas in the passage. This question is worth 2 points.
Paragraph 1
The theory of evolution by natural selection, first comprehensively formulated by Charles Darwin in his 1859 book On the Origin of Species, is the foundational principle of all modern biology. It provides a rational, evidence-based explanation for the immense diversity of life on Earth and the remarkable ways in which organisms are adapted to their environments. The theory is built upon a few key observations and inferences. Darwin observed that organisms produce more offspring than can possibly survive, that there is variation among individuals within a species, and that these variations are heritable. From these observations, he inferred that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits on to the next generation.
Paragraph 2
The core mechanism of the theory is natural selection, often summarized as 'survival of the fittest.' However, this phrase can be misleading. 'Fitness' in a biological context does not refer to physical strength or health, but rather to an organism's reproductive success—its ability to pass its genes on. Natural selection is the process whereby environmental pressures—such as predation, climate, and competition for resources—'select' for certain heritable traits. For example, in a forest inhabited by sharp-eyed predators, brown beetles may survive and reproduce more effectively than bright green beetles because they are better camouflaged. Over generations, this differential survival and reproduction leads to an increase in the frequency of the brown coloration trait in the population.
Paragraph 3
For natural selection to operate, there must be variation within a population. Without variation, all individuals would be identical, and there would be no traits to select for. The ultimate source of all new genetic variation is random mutation—changes in the DNA sequence. While most mutations are neutral or harmful, occasionally a mutation arises that confers a survival or reproductive advantage. Sexual reproduction is another major source of variation, as it shuffles existing parental genes into new combinations in the offspring. This constant generation of new variations provides the raw material upon which natural selection can act, allowing populations to adapt to changing environmental conditions over time.
Paragraph 4
The evidence for evolution by natural selection is vast and comes from many different fields of science. The fossil record provides a clear history of life on Earth, showing the gradual changes in organisms over geological time and the emergence of new species from ancestral forms. Comparative anatomy reveals homologous structures—features like the pentadactyl (five-fingered) limb found in humans, bats, whales, and cats—which share a common underlying structure despite their different functions, pointing to a common ancestor. Biogeography, the study of the distribution of species, shows that closely related species are often found in close geographic proximity, supporting the idea that they diverged from a local ancestor. Finally, modern genetics and molecular biology provide the most direct evidence, allowing scientists to compare DNA sequences and demonstrate the precise genetic relationships between different species.
Paragraph 5
It is crucial to understand that evolution by natural selection is not a random process, nor does it have a predetermined goal. While the underlying source of variation (mutation) is random, the process of selection itself is non-random. It consistently favors traits that enhance reproductive success in a specific environment. Evolution does not strive to create 'perfect' organisms; it simply adapts populations to their current circumstances. A trait that is advantageous in one environment might be neutral or detrimental in another. The theory provides a powerful framework for understanding not only the history of life but also pressing contemporary issues, such as the evolution of antibiotic resistance in bacteria and the conservation of biodiversity in a rapidly changing world.
The word 'foundational' in paragraph 1 is closest in meaning to...
The word 'detrimental' in paragraph 5 is closest in meaning to...
According to paragraph 2, what is the biological definition of 'fitness'?
What can be inferred from the example of the brown and green beetles in paragraph 2?
According to paragraph 3, what is the ultimate source of all new genetic variation?
Why does the author mention homologous structures in paragraph 4?
What does the author imply about the process of natural selection in paragraph 5?
Which of the following is NOT listed in paragraph 4 as a source of evidence for evolution?
Look at the four squares [■] that indicate where the following sentence could be added to paragraph 2. Where would the sentence best fit?
This leads to adaptation, the process by which populations become better suited to their environment over time.
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The theory of evolution by natural selection explains that life's diversity is the result of organisms adapting to their environments over time.
Select 3 answer choices that express the most important ideas in the passage. This question is worth 2 points.