Demographic Puzzles

1. In 1990, the United States had a crude death rate (deaths per 1000 persons) of 8.6 and Mexico had a crude death rate of 5.3. But at every age, the United States had a lower age-specific death rate than Mexico. How can this be?

2. Most women are physiologically capable of having a birth every year for 25-30 years of reproductive life. But no population in recorded history has an average completed family size for women as high as 10. Why?

3. Each person has two biological parents, four biological grandparents, eight great-grandparents and son on. The number of your "lineal progenitors" n generations ago is simply 2ⁿ. Thirty generations ago, or approximately 900 years, each of you had 2³⁰ = 1.07 billion lineal progenitors. But the total world population 900 years ago was only about 1/4 billion. How can this be?

4. In the United States, women aged 45-49 in 1950 (who reached prime reproductive ages during the depression) had borne an average of only 2.29 children. Yet their children had, on average, 3.91 siblings, for a total average sibship size of 4.91. Explain.

5. A huge reduction in mortality occurred in Asia between 1950 and 1960, with no change in rates of childbearing or immigration. But the mean age of the population actually fell between these dates. Why?