Struggle for existence and survival of fittest are related to `:`

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Terms:**
- The phrase "struggle for existence" refers to the competition among organisms for limited resources such as food, space, and mates.
- "Survival of the fittest" is a concept that describes how certain individuals are better adapted to their environment and thus have a higher chance of surviving and reproducing.

2. **Identifying the Scientist:**
- The question asks which scientist is associated with these concepts. The two prominent figures in evolutionary biology are Charles Darwin and Alfred Russel Wallace.
- Darwin is particularly well-known for his contributions to the theory of natural selection.

3. **Darwin's Theory:**
- Charles Darwin proposed that in the struggle for existence, those organisms that are better adapted to their environment (the "fittest") are more likely to survive and reproduce.
- This concept is encapsulated in his theory of natural selection, which explains how species evolve over time.

4. **Conclusion:**
- Based on the information, the struggle for existence and survival of the fittest are primarily related to Charles Darwin's theory of natural selection.

5. **Final Answer:**
- The correct answer is **B. Darwin**.

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