Pre-industrial fertility & mortality
Death rates in pre-industrial societies were very high, especially among infants and children. In order to compensate for high infant and child mortality, women had around seven children over the course of their lifetimes (not including pregnancy losses, which are believed to have been much higher in the past). Unfortunately, infant mortality was so prevalent that records are very scarce and likely underreported; but conservative estimates suggest that roughly one quarter of infants did not see their first birthday, and only half of those born would make it to adolescence. In most individual years, birth rates exceeded death rates and this led to population growth, but regular famines or pandemics caused spikes in mortality, which reduced average population growth over longer periods. It is estimated that the world's population growth was just 0.04 percent per year between 10,000 BCE and the 19th century.Historical pandemics
The deadliest pandemics in history were caused by plague and smallpox; waves of these pandemics famously decimated the populations of Europe and the Americas, but they could also become endemic for longer periods. In many instances, smallpox became an accepted fact of life; there is even some evidence of families waiting until children had contracted the virus before naming them. Plague was mostly eradicated through improved infrastructure, rodent extermination, and distancing methods, but it was not until the development of the smallpox vaccination in 1796 that its effects began to dissipate; the final naturally-occurring case was recorded in 1977, and it remains the only human disease to have been eradicated in nature. Alongside improvements in sanitation and food stability, and better understanding of germ theory, widespread vaccination generally marks the beginning of a drastic decline in child mortality, which sees the onset of societies’ demographic transitions.Urban and regional variations
There was also variation by time and region; across the second millennium, Japan’s isolation and cultural traits offered protection from many pandemics and water-borne viruses, while imported crops from the Americas and agricultural advancements saw a rise in Western Europe’s life expectancy, leading to population growth. The Americas arguably underwent the most drastic demographic change after 1492; it took almost four centuries for its population to return to pre-colonization levels, by which point European migration and transatlantic slavery had greatly altered the ethnic composition of the continent. Urbanization also played a major part in demographic development; until the 1800s, fewer than five percent of the world's population lived in urban centers. This was due to the general dependency on subsistence agriculture; the vast majority of people lived on small holdings producing their own food, while urbanized areas were generally centered around ports, markets, or administrative centers. Urbanization is a relatively new phenomenon, and correlates with the industrial maturity of a country or region. In its early phase, urbanization often leads to higher mortality due to the more rapid spread of disease and a lack of sanitation infrastructure, but prosperity eventually results in higher living standards. Regional imbalances in industrialization and economic development also correlate with demographic development today, for example, Sub-Saharan Africa was the last major region to industrialize, doing so in the early-1900s, and some demographic trends are still in line with pre-industrial times (such as Niger’s fertility rate).
