Sudden reappearance of certain ancestral chracters which had either disappeared or were reduced is known as

Options

A. Adaptive radiation
B. Atavism
C. Convergent evolution
D. Phylogeny

Answer

To solve the question regarding the sudden reappearance of certain ancestral characters that had either disappeared or were reduced, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept**:
- The question refers to a phenomenon where traits that were present in ancestral species but have since disappeared or diminished reappear in later generations.

2. **Identifying the Term**:
- This phenomenon is known as "atavism." Atavism refers to the re-emergence of traits that were present in distant ancestors but are not typically seen in the immediate ancestors.

3. **Example of Atavism**:
- A classic example of atavism is the reappearance of tails in some individuals of species that typically do not have tails. For instance, humans have a vestigial tailbone (coccyx), but in rare cases, individuals may be born with a tail due to genetic mutations.

4. **Differentiating from Other Terms**:
- It is important to differentiate atavism from other biological concepts:
- **Adaptive Radiation**: This is the process where organisms diversify rapidly into a variety of forms to adapt to different environments.
- **Convergent Evolution**: This occurs when unrelated species evolve similar traits due to similar environmental pressures, not because they share a common ancestor.
- **Phylogeny**: This is the study of the evolutionary history and relationships among individuals or groups of organisms.

5. **Conclusion**:
- Based on the definition and examples, the correct answer to the question is "atavism."

### Final Answer:
The sudden reappearance of certain ancestral characters which had either disappeared or were reduced is known as **Atavism**.

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