Which of the following observations led to Darwin's major inferences about natural selection?

• A. Individuals in a population vary in their heritable traits.
• B. Populations always remain the same size regardless of environmental conditions.
• C. Acquired characteristics are inherited by offspring.
• D. All individuals in a population have identical traits.

Answer: (A)

Verified step by step guidance

1. Understand the concept of natural selection: Natural selection is the process by which individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to the next generation.
2. Review Darwin's observations: Darwin observed that individuals in a population exhibit variation in their traits, and these traits can be inherited by offspring. This variation is crucial for natural selection to act upon.
3. Eliminate incorrect options: Analyze the provided options. For example, 'Populations always remain the same size regardless of environmental conditions' is incorrect because populations are influenced by factors like resource availability and predation. Similarly, 'Acquired characteristics are inherited by offspring' is incorrect because traits acquired during an individual's lifetime (e.g., muscle growth) are not passed genetically. Lastly, 'All individuals in a population have identical traits' is incorrect because variation is a key component of natural selection.
4. Identify the correct observation: The correct observation is 'Individuals in a population vary in their heritable traits,' as this variation provides the raw material for natural selection to act upon.
5. Connect the observation to Darwin's inference: Darwin inferred that individuals with advantageous heritable traits are more likely to survive and reproduce, leading to the gradual adaptation of populations to their environments over generations.