describe how the composition of the population changed ? Solution The major reason for population changes, whether in an individual country or for the whole world, is the change in birth and death rates. The birth rate is the number of live babies born in a year for every 1000 people in the total population. Death rates are number of people dying per 1000 people. When birth rates are higher than death rates the population of an area will increase. migration are the number of people migrate from one country or society to the other. BIRTH RATE: when babies are born, it results in a population change, The fertility rate in a country refers simply to the number of children born. This is different from the fecundity rate, which is the number of children who could be born in a given society. In other words, fecundity is the biological capacity of humans to produce children.The fecundity rate is greater than the fertility rate in most cases. Birth rates vary by society for a number of reasons, including personal choice and social and political factors. Factors such as poverty level, access to contraception, maternal and infant care, and availability of nutrition all impact the birth rate in a society. DEATH RATE: As the growth rates increases the death rate also increases. when babies are born, when members of a society die it changes the population. butthis is refered as the mortality rate, which is simply the number of deaths that occur in a society. This is usually calculated by looking at the number of deaths per 1,000 individuals. In the United States, for example, the death rate is 8/1000 people. Just like birth rate, the death rate in a country depends on things such as availability of quality medical care, disease, war, or famine. MORTALITY: The most important factor that accounts for a change in population is migration. Generally migration refers to movement; it\'s the flow or circulation of people in societies. There are two kinds of migration: emigration and immigration. Emigration means to leave one\'s own country for another. Immigration means to enter into a country other than one\'s own. Both of these process impact population change. The composition also depends upon age structure. Age structure varies according to age distribution of an individual, therefore the population size is expected to double or even triple before stabilizing for many developing countries with fairly large populations and large numbers of people under age 15..