Which one of the following was not explained by the Darwinism?

Options

A. Natural selection
B. Struggle for existence
C. Arrival of the fittest
D. Origin of species

Explanation

**Step-by-Step Solution:**

1. **Understanding Darwinism**: Darwinism refers to the theory of biological evolution developed by Charles Darwin, which emphasizes natural selection as the mechanism of evolution.

2. **Identifying Key Concepts**: The main concepts associated with Darwinism include:
- **Natural Selection**: The process by which organisms better adapted to their environment tend to survive and produce more offspring.
- **Struggle for Existence**: The competition among organisms for resources necessary for survival.
- **Survival of the Fittest**: A phrase often associated with Darwin, indicating that those best suited to their environment are more likely to survive and reproduce.
- **Origin of Species**: The title of Darwin's seminal work where he outlines his theories.

3. **Analyzing the Options**: The question provides four options:
- Natural Selection
- Struggle for Existence
- Arrival of the Fittest
- Origin of Species

4. **Evaluating Each Option**:
- **Natural Selection**: Explained by Darwin as a key mechanism of evolution.
- **Struggle for Existence**: Also explained by Darwin as a fundamental aspect of survival.
- **Origin of Species**: This is the title of Darwin's book where he discusses his theories.
- **Arrival of the Fittest**: This phrase is not part of Darwin's theory. Instead, Darwin focused on the survival of those already present in the environment rather than the emergence of new species or forms.

5. **Conclusion**: Based on the analysis, the option that was not explained by Darwinism is **Arrival of the Fittest**.

**Final Answer**: Arrival of the Fittest

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