Separating, somewhat artificially, the now more developed from the less developed regions, one can estimate that, in periods up to about 1850, in both sets of regions there was an average of about 35 deaths and about 40 births per 1,000 inhabitants each year, leaving similarly moderate balances of a natural increase in both sets of regions. But, after 1850, the annual average death rate in the now more developed regions decreased to about 28 per 1,000 in 1850-1900, to about 18 per 1,000 in 1900-1950, and up to 10 per 1,000 since 1950. In the now less developed regions the death rate may have averaged 38 per 1,000 during 1850-1900, and was still 32 per 1,000 during 1900-1950, as compared with an estimated 21 per 1,000 in 1950-1960, and 17 per 1,000 in 1960-1970. In these regions, as compared with the more developed ones, the modern diminution of mortality was delayed by nearly a century but now it is occurring with outstanding speed. Severe inequalities in risk of death still persist between the inhabitants of more developed and less developed regions, but at least it can justifiably be said that the gap, which was at its widest in the first half of this century, is now narrowing considerably. Nevertheless, there is a wide range between different regions and countries: in the less developed countries mortality rates in 1970-1980 vary between 4 and 46 and in the more developed countries between 7 and 21.
Due to the more youthful structure of their populations, the frequency of death (per 1,000 inhabitants of all ages) in some of the less developed countries has now fallen as low as, or even lower than, that in some of the more developed countries where the proportion of individuals at advanced ages is high.