Select the incorrect statement:

Options

A. An overwheliming majority of animals and nearly all plants maintian a constant internal environment
B. An orchid growing as an epiphyte on a mango branch is an example of commensalism
C. In brood parasitism, the parasite bird lays its eggs in the nest of its host and lets the host to incubate them
D. Very small animals are rarely found in polar regions

Answer

To determine the incorrect statement from the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement**:
- The statement claims that "an overwhelming majority of animals and nearly all plants maintain a constant internal environment."
- This statement is incorrect because most animals and plants do not maintain a constant internal environment. Their body temperature often changes with the ambient temperature. For example, ectothermic animals (like reptiles) and many plants adjust their physiological processes according to the external environment.

2. **Analyze the Second Statement**:
- The statement mentions that "an orchid growing as an epiphyte on a mango branch is an example of commensalism."
- This statement is correct. In this relationship, the orchid benefits by gaining a place to grow and access to sunlight, while the mango tree is neither harmed nor benefited. Therefore, this is a classic example of commensalism.

3. **Analyze the Third Statement**:
- The statement describes "brood parasitism" where "the parasite bird lays its egg in the nest of its host and lets the host incubate them."
- This statement is also correct. In brood parasitism, the parasite bird (like the cuckoo) lays its eggs in the nests of other birds, and the host birds incubate and raise the young, often at their own expense.

4. **Analyze the Fourth Statement**:
- The statement states that "very small animals are rarely found in the polar region."
- This statement is correct as well. Smaller animals have a larger surface area relative to their volume, which leads to rapid heat loss in cold environments. This adaptation makes it difficult for them to survive in polar regions.

### Conclusion:
After analyzing all the statements, the incorrect statement is the **first statement** regarding the maintenance of a constant internal environment by animals and plants.

### Final Answer:
The incorrect statement is: **"An overwhelming majority of animals and nearly all plants maintain a constant internal environment."**

---