I. The Age Transition
Migration, mortality and fertility operate differently to create inequalities in the ratio of males to females; this is known at the sex ratio. To determine the sex ratio you must determine the number of males, divide by the number of females and multiply by 100, this number equals the sex ratio. If the sex ratio is greater than 100 then there are a greater number of males than females, reversely, if the sex ratio is less than 100 then there are a greater number of females. However, the sex ratio is typically male dominate. This is a due to the fact that in virtually every human society more boys are born than girls. The typical sex ratio range is 104-110. The US tends to be on the low end of this trend, while China is on the high end. Chinese culture dictates that males are more valuable than females, so since in-utero sex id has been available, more sex specific abortions have taken place.
The population pyramid, also known as the age pyramid is a graphic representation of the distribution of a population by age and sex. The shape resembles a pyramid because the “classic” picture of a population is of a high fertility, high mortality society with a broad base built of numerous births, rapidly tapering to the top because of high death rates in combination with high birth rates. This classic pyramid was the norm in Mexico till the decline in fertility since the 1970s. Since the 70s the pyramid has begun to noticeably narrow at the base, meaning less births. One can conclude that Mexican’s, who once valued child birth as a religious duty, have shifted views over the past three decades. This may be in part to higher education, more migration and lower fertility rates. In comparison, the US population pyramid more resembles a rectangular age and sex distribution. This rectangular shape can be interpreted to mean that the US fertility is currently at the replacement level, births are replacing deaths. The US is a nation that has over the...