Why do new-born mammals usually do not shiver in spite of lower temperature outside mother's womb?

Options

A. Due to presence of areolar tissue beneath the skin
B. Due to presence of brown fat
C. Due to presence of both brown fat and white fat
D. Due to presence of white fat

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why newborn mammals do not shiver despite being in a lower temperature environment outside the mother's womb.

2. **Identifying Key Factors**: Newborn mammals have a unique physiological characteristic that differentiates them from adults, particularly in terms of fat storage and thermoregulation.

3. **Role of Adipose Tissue**: Newborns have a significant amount of adipose tissue, which is a type of connective tissue that stores fat. This tissue plays a crucial role in insulation and energy storage.

4. **Types of Adipose Tissue**:
- **White Fat**: This type of fat primarily serves as an energy reserve and is stored in the form of lipid droplets.
- **Brown Fat**: This type is metabolically active and is rich in mitochondria. It is responsible for thermogenesis (heat production) by burning calories and breaking down fats.

5. **Thermoregulation in Newborns**: Newborn mammals have a higher proportion of brown fat compared to white fat. The presence of brown fat allows them to generate heat without shivering, which is a response typically seen in adults to maintain body temperature.

6. **Conclusion**: Therefore, the reason newborn mammals do not shiver in lower temperatures is due to the presence of brown fat, which provides insulation and generates heat through metabolic activity.

7. **Final Answer**: The correct answer is the presence of brown fat.

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