We sometimes find the existence of following structures in human beings:
(a) Occurrence of short tail in some babies
(b) Presence of additional mammae in two rows down the front of the body of some persons
(c) Power of moving pinna, or
(d) Presence of very long and dense hair on the body.
Why does this happen in some persons? Also, name the phenomenon involved.

Explanation

### Step-by-Step Solution:

1. **Understanding the Structures**:
- The question lists certain structures found in some human beings: short tails in babies, additional mammae, the ability to move the pinna, and long dense body hair.

2. **Identifying the Common Theme**:
- All these structures are not commonly found in every individual but appear in some. This suggests a genetic or evolutionary basis for their occurrence.

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