diminished the benefits and increased the costs of raising children. In other words, it became more economically sensible to invest more in fewer children. This is known as the first demographic transition. This trend continued till around 1950. (The second demographic transition occurred due to the significant cultural shifts of the 1960s, leading to the decline in the desire for children.) Fertility rates and mortality rates The demographic transition is when a population shifts from being one of high child mortality rates and high fertility rates to one that is low in both. Western nations completed this transition by the early 1900s. It occurred in two stages. Initially, child mortality rates dropped significantly due to improved healthcare and sanitation and better nutrition, yet fertility rates remained high, leading to a population boom. Gradually, fertility rates fell as people became more affluent and had better access to contraception. By 1900, the infant mortality rate in England was 10 percent, down from an estimated 25 percent in the Middle Ages. There was no catastrophic epidemic or famine in England or Scotland in the nineteenth century—it was the first century in which a major epidemic did not occur throughout the whole country, and deaths per 1000 of population per year in England and Wales fell from 21.9 from 1848 to 1854 to 17 in 1901 (cf, for instance, 5.4 in 1971). Social class had a significant effect on mortality rates: the upper classes had a lower rate of premature death early in the nineteenth century than poorer classes did. In the Victorian era, fertility rates increased in every decade until 1901, when the rates started evening out. There were several reasons for this. One is biological: with improving living standards, a higher proportion of women were biologically able to have children. Another possible explanation is social. In the 19th century, the marriage rate increased, and people were getting married at a very young age until the end of the century, when the average age of marriage started to increase again slowly. The reasons why people got married younger and more frequently are uncertain. One theory is that greater prosperity allowed people to finance marriage and new households earlier than previously possible. With more births within marriage, it seems inevitable that marriage rates and birth rates would rise together. Birth rates were originally measured by the 'crude birth rate' – births per year divided