In order for the human population to achieve zero population growth which of the following must occur ?

Options

A. There must be more postreproductive individuals than reproductive individuals.
B. There must be more prepreproductive than reproductive individuals
C. There must be the same number prereproductive individuals as there are reproductive individuals.
D. all of these

Answer

To determine the conditions necessary for the human population to achieve zero population growth, we need to understand the concept of zero population growth (ZPG). ZPG occurs when the birth rate equals the death rate, resulting in a stable population size. Let's analyze the options provided in the question step-by-step.

### Step-by-Step Solution:

1. **Understanding Zero Population Growth (ZPG)**:
- Zero population growth means that the number of births in a population is equal to the number of deaths. This leads to a stable population size where there is no net increase or decrease.

2. **Identifying Population Stages**:
- There are three stages of population:
- **Post-Reproductive Stage**: Individuals in this stage cannot give birth.
- **Reproductive Stage**: Individuals in this stage can give birth.
- **Pre-Reproductive Stage**: Individuals in this stage are not yet able to give birth but will enter the reproductive stage later.

3. **Analyzing the Options**:
- **Option A**: There must be more post-reproductive individuals than reproductive individuals.
- If there are more post-reproductive individuals, it means fewer individuals can reproduce, leading to a decrease in the birth rate. This would not achieve ZPG.

- **Option B**: There must be more pre-reproductive individuals than reproductive individuals.
- If there are more pre-reproductive individuals, they cannot reproduce yet. If the reproductive individuals are fewer, the birth rate will decrease, leading to a decline in population, not ZPG.

- **Option C**: There must be the same number of pre-reproductive individuals as there are reproductive individuals.
- If the number of pre-reproductive individuals equals the number of reproductive individuals, the reproductive individuals can give birth, and the population can stabilize. This condition can lead to ZPG as the birth rate can match the death rate.

- **Option D**: All of these.
- Since options A and B do not support achieving ZPG, this option is incorrect.

4. **Conclusion**:
- The correct condition for achieving zero population growth is **Option C**: There must be the same number of pre-reproductive individuals as there are reproductive individuals.

### Final Answer:
The correct answer is **Option C**: There must be the same number of pre-reproductive individuals as there are reproductive individuals.

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