Which one has a real existence?

Options

A. Kingdom
B. Phylum
C. Genus
D. Species

Answer

### Step-by-Step Solution:

1. **Understanding Taxonomy**: Taxonomy is the science of classification of living organisms. It includes various hierarchical categories such as kingdom, phylum, class, order, family, genus, and species.

2. **Identifying Real vs. Theoretical Existence**: In taxonomy, higher categories like phylum, class, and genus are often considered to have a theoretical existence. This means they are classifications created by humans for convenience in organizing and understanding biological diversity.

3. **Defining Species**: The species is the basic unit of classification and is defined as a group of interbreeding populations that can produce fertile offspring. This definition indicates that species have a real, tangible existence in nature.

4. **Examples for Clarity**: For instance, if we consider the domestic cat:
- **Species**: Felis catus (this has a real existence as it refers to actual cats we see).
- **Genus**: Felis (this is a broader classification that includes several species of small cats, but it is more theoretical).
- **Family**: Felidae (this includes all cats, but again, it is a theoretical grouping).

5. **Conclusion**: Based on the above understanding, the only category that has a real existence in the biological world is the species. Therefore, the correct answer to the question "Which one has a real existence?" is **species**.

### Final Answer:
The species has a real existence.

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