Many animals have not evolved to become thermoregulators because

Options

A. there are no perfect regulators
B. thermoregulation is energetically expensive process
C. the 'benefit' of thermoregulation is more than the 'cost' they would incur
D. thermoregulators are found only in tropical regions

Answer

### Step-by-Step Solution

1. **Understanding Thermoregulation**:
- Thermoregulation refers to the ability of an organism to maintain a stable internal body temperature regardless of external environmental conditions. This process is crucial for the survival of many animals.

2. **Energy Requirements**:
- The process of thermoregulation requires a significant amount of energy. Animals must expend energy to generate heat when it is cold and to dissipate heat when it is hot. This energy expenditure can be energetically expensive.

3. **Conformers vs. Regulators**:
- Organisms can be classified into two categories: conformers and regulators.
- **Conformers**: Their internal environment changes in accordance with the external environment. They do not maintain a constant internal temperature.
- **Regulators**: They maintain a constant internal environment despite changes in the external environment. This ability requires energy.

4. **Cost-Benefit Analysis**:
- For many animals, especially smaller ones, the cost of thermoregulation outweighs the benefits. Small animals have a high surface area-to-volume ratio, leading to rapid heat loss. Thus, maintaining a constant temperature becomes challenging and energetically costly.

5. **Conclusion**:
- Many animals have not evolved to become thermoregulators primarily because thermoregulation is an energetically expensive process. This is especially true for smaller animals that struggle to maintain their body temperature due to their high surface area-to-volume ratio.