By Pei Gao (NYU Shanghai) & Eric B. Schneider (LSE)
Since the mid-nineteenth century, the average height of adult British men increased by 11 centimetres. This increase in final height reflects improvements in living standards and health, and provides insights on the growth pattern of children which has been comparatively neglected. Child growth is very sensitive to economic and social conditions: children with limited nutrition or who suffer from chronic disease, grow more slowly than healthy children. Thus, to achieve such a large increase in adult height, health conditions must have improved dramatically for children since the mid-nineteenth century.
Our paper seeks to understand how child growth changed over time as adult height was increasing. Child growth follows a typical pattern shown in Figure 1. The graph on the left shows the height by age curve for modern healthy children, and the graph on the right shows the change in height at each age (height velocity). We look at three dimensions of the growth pattern of children: the final adult height that children achieve, i.e. what historians have predominantly focused on to date; the timing (age) when the growth velocity peaks during puberty, and, finally, the overall speed of maturation which affects the velocity of growth across all ages and the length of the growing years.
Figure 1. Weights and Heights for boys who trained on HMS Indefatigable, 1860s-1990s.
To understand how growth changed over time, we collected information about 11,548 boys who were admitted to the training ship Indefatigable from the 1860s to 1990s (Figure 2). This ship was located on the River Mersey near Liverpool for much of its history and it trained boys for careers in the merchant marine and navy. Crucially, the administrators recorded the boys’ heights and weights at admission and discharge, allowing us to calculate growth velocities for each individual.
Figure 2. HMS Indefatigable
We trace the boys’ heights over time (grouping them by birth decade) and find that they grew most rapidly during the interwar period. In addition, the most novel finding was that for boys born in the nineteenth century there is little evidence that they experienced a strong pubertal growth spurt unlike healthy boys today. Their growth velocity was relatively flat across puberty. However, starting with the 1910 birth decade, boys began experiencing more rapid pubertal growth similar to the right-hand graph in Figure 1. The appearance of rapid pubertal growth is a product of two factors: an increase in the speed of maturation, which meant that boys grew more rapidly during puberty than before and, secondly, a decrease in the variation in the timing of the pubertal growth spurt, which meant that boys were experiencing their pubertal growth at more similar ages.
Figure 3. Adjusted height-velocity for boys who trained on HMS Indefatigable.
This sudden change in the growth pattern of children is a new finding that is not predicted by the historical or medical literature. In the paper, we show that this change cannot be explained by improvements in living standards on the ship and that it is robust to a number of potential alternative explanations. We argue that reductions in disease exposure and illness were likely the biggest contributing factor. Infant mortality rates, an indicator of chronic illness in childhood, declined only after 1900 in England and Wales, so a decline in illness in childhood could have mattered. In addition, although general levels of nutrition were more than adequate by the turn of the twentieth century, the introduction of free school meals and the milk-in-schools programme in the early twentieth century, likely also helped ensure that children had access to key protein and nutrients necessary for growth.
Our findings matter for two reasons. First, they help complete the fragmented picture in the existing historical literature on how children’s growth changed over time. Second, they highlight the importance of the 1910s and the interwar period as a turning point in child growth. Existing research on adult heights has already shown that the interwar period was a period of rapid growth for children, but our results further explain how and why child growth accelerated in that period.
Eric B. Schneider