Answers for "Check Yourself" questions: Current Population

(1) The global population is growing at 1.2% per year (given on the fact sheet by "Rate of Natural Increase [%]). Recall that this is equal to r * 100, where r is the net reproduction per individual = b - d. (Click on History to review these demographic parameters.)

Thus, "r" for humans is currently = 0.012. This means that for every 100 people, we now have a net gain of 1.2 persons.

(2) Not necessarily. Remember, G = rN. While r (the multiplier -- the rate of net reproduction per individual) has decreased, N has increased tremendously since 1970, and thus G has not declined as rapidly as r has declined..

(3) No. As we just demonstrated, you need information about the population's age structure as well as about its TFR to predict its growth. If you knew only the US's TFR, you would say that it is not growing, which is not true.

(4) It makes a great deal of difference. For example, in 60 years, you could "fit" only two generations if people delay reproduction until they are 30 years old, while you could "fit" three generations into that time if the average age of first reproduction were decreased to 20 years. (This is simplistic, of course, but I hope that you get the idea.) Particularly if the population is one with a high per capita rate of reproduction ('r" ), this difference in number of generations would translate rapidly into a huge difference in population growth. You can calculate the effect of generation time on "r" as:

r = natural log (ln) of the net reproductive rate for females (the average production of female offspring per female per generation) divided by the mean generation time in years.

Since the calculation divides by mean generation length, you can see that the generation length is very important. As a hypothetical example, if the net reproductive rate for females were 0.1 and the generation length were 20 years, we would have "r" = 0.005 (= 0.1 / 20). If, on the other hand, generation length was increased to 30 years, we would have "r" = 0.003 (= 0.1 / 30). Nearly a halving of "r" just by lengthening generations from 20 years to 30 years!

(5) India will add approximately 19.2 million people

China will add approximately 6.8 million people

(Remember G = r*N , where r is not a percentage. Thus, for India, G = 1.28 billion * 0.015 = 19.2 million and for China G = 1.36 billion * 0.005 = 6.75 million.)

(6) While we don't often think of them as being pronatalist, policies such as income tax deductions for dependent children and maternity and paternity leaves are essentially that. (There are good reasons for these policies being in place, of course, but they also certainly don't act to discourage having large numbers of children...)

Because they are essentially pronatalist policies, they have been eliminated in some nations that are seeking stabilization in population. For example, income tax deductions for dependent children have been eliminated in Tanzania, Sri Lanka and Nepal.

By contrast, some of the slow (or negative) growth nations in the world are actually beginning to institute more and more of these pronatalist policies, in response to concern about dwindling populations. Some nations actually are paying couples for each child that they have!!

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This page is maintained by Patricia Muir at Oregon State University. You can address comments or questions to me here (muirp@science.oregonstate.edu). Page last updated Nov. 15, 2013.

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