Questions: What is the primary determinate of future human population size estimates?

The answer is the second one: How many children each woman decides to have.

Explanation for each option:

1. The number of elderly women: This is not the primary determinant of future human population size. While the number of elderly women can affect population demographics, it does not directly influence the growth rate of the population.

2. How many children each woman decides to have: This is the correct answer. The fertility rate, or the average number of children born to a woman over her lifetime, is a crucial factor in determining future population size. Higher fertility rates lead to larger population growth, while lower fertility rates can lead to population stabilization or decline.

3. The number of predators: This is not relevant to human population size. Humans do not have natural predators that significantly impact population size.

4. The amount of space on Earth: While space can influence population density and distribution, it is not the primary determinant of population size. Human populations can grow or shrink regardless of the amount of available space.

5. The amount of food present on Earth: Although food availability is important for sustaining populations, it is not the primary determinant of future population size. Advances in technology and agriculture can alter food production and distribution, but fertility rates are more directly linked to population growth.

Summary: The primary determinant of future human population size estimates is how many children each woman decides to have. This factor directly influences the fertility rate, which is a key driver of population growth.