by total population. This is indeed a crude measure, as key groups and their fertility rates are not clear. It is likely to be affected mainly by changes in the age distribution of the population. The Net Reproduction Rate was then introduced as an alternative measure: it measures the average fertility rate of women of child-bearing ages. High rates of birth also occurred because of a lack of birth control. Mainly because women lacked knowledge of birth control methods and the practice was seen as unrespectable. The evening out of fertility rates at the beginning of the 20th century was mainly the result of a few big changes: availability of forms of birth control, and changes in people's attitude towards sex. In the olden days, people typically had had as many children as they could afford in order to ensure at least a few of them would survive to adulthood and have children of their own due to high child mortality rates. Moreover, it was the poor who had had an incentive to curb their fertility whereas the rich had lacked such a need due to greater wealth and lower child mortality rates. This changed due to the Industrial Revolution. Standards of living improved and mortality rates fell. People no longer needed to have as many children as before to ensure the propagation of their genes. The link between poverty and child mortality weakened. In addition, societal attitude towards contraception warmed, leading to the negative correlation between intelligence and fertility. Factors linked to general intelligence, such as socioeconomic status and educational attainment, were also found to be negatively correlated with fertility starting from the nineteenth century. Environmental and health standards rose throughout the Victorian era. Improvements in nutrition may also have played a role, though its importance is still debated. Economy, industry, and trade Progress Life in the late 1700s had been little different from life in the late Middle Ages. But the nineteenth century saw dramatic technological development. Someone alive in 1804 would know about the electric telegraph, the steam ship, the circular saw, the bicycle, and the steam-powered locomotive. If this person lived to 1870, he or she would have heard of the invention of the electric light bulb, the typewriter, the calculator, the rubber tyre, the washing machine, the internal combustion engine, plastic, and dynamite. Engineering prowess, especially in communication and transportation, made Great Britain the leading