“The secular trend in human physical growth is a natural experiment which highlights the complex interplay between genes, physiology and environment in determining the size and shape of individuals from one generation to the next.”
(Cole 2003: 165)
As briefly discussed in the section on genetic influences on growth, a population experiencing environmental changes can show changing patterns in skeletal traits through time, which do not have a genetic origin. Commonly, the measure of these changes is stature and the observed change is called a secular trend (Hauspie et al.
1997). Secular trends relate to changes in the nutritional and disease environment as well as economic and political factors. Changes through time can be observed by examining statures between groups within the population or in the population as a whole. What is evident from the literature is that there is no uniform context in which
50
a secular change in height occurs but a variety of improving conditions that result in an increase in the standard of living in a population or worsening conditions that result in a decrease (Cole 2003; Floud et al. 1990; Hauspie et al. 1997; Komlos 1995). Published studies on secular trends with regard to appositional bone growth are limited and tend to focus on change over extensive periods of time, such as thousands (Macintosh et al. 2014; Ruff et al. 2015) or even millions of years, covering the entire Homo lineage (Ruff 2006). The general pattern in these studies has been gracialisation over time, which is argued to be related to changes in subsistence related activity patterns. Recently, Ruff et al. (2015) presented evidence that in Europe, the last notable decrease in bone strength and resistance to bending occurred during the beginning of the Neolithic. Some signs of gracialisation were observed through the Iron and Roman periods but no further changes were observed in more recent populations, latest of which were from the 20th century. The Finnish population studied here is included in Ruff et al.’s (2015) sample of ‘very recent’ humans. However, they use it just as a single data point as part of a pooled 19th and 20th century European comparative sample, and they do not take into account variation through time within the Finnish population, which is the focus of the current study.
Variation in the nutritional and disease environment seem to be important drivers of secular change in height (Mays et al. 2009) and this has been demonstrated for example by Bogin (1999) in his research on the Maya of Guatemala and the children of Maya immigrants brought up in the USA, who showed increased stature compared to their parents’ generation. The Maya children living in the US had access to better nutrition as well as lesser disease burden early in life (Bogin 1999).
This intergenerational difference in height also provides strong evidence for the argument that within population height differences are not entirely due to changes in gene frequencies but at least in part response to an improved living environment. A further example of the effect of socio-economic change on stature comes from Papua New Guinea, where a significant secular increase in children’s statures was observed among the small-scale Mountain Ok population after the opening of a mine, which greatly increased the population’s wealth and access to nutrition (Adhikari et al. 2011). Secular change has also been studied using skeletal remains, for instance, the long bone lengths of both Black and White Americans were inspected using multiple collections dated up to the 1970s (Jantz and Jantz 1999).
51
The study found that the lower limb long bones showed secular changes more clearly than the upper limb, and that changes were stronger in men than in women.
It concludes that the cumulative environmental conditions the study individuals were exposed during growth have improved over the last 200 years (Jantz and Jantz 1999). This supports the evidence from historical studied on secular changes in Western countries, discussed below.
In the Western world, the general trend of secular change in growth has been an increase in stature and growth velocity since the 19th century (Cole 2000). This follows, to an extent, the demographic and subsistence change from agrarian societies towards industrialised states (Hauspie et al. 1997). The industrial revolution itself, however, was followed by a decrease in stature in many European countries in late 18th and early 19th century (Cole 2000), as despite a rapidly growing economy (Komlos 1998), increasing numbers of people lived in overcrowded and poorly sanitized cities without adequate nutrition (Komlos 1995). The epidemiological transition occurred in many European countries well after industrialisation and English cities, for example, suffered from cholera outbreaks until the 1860s (Sharpe 2012). Thus, despite steady economic growth, the health of especially the poorest part of the population was not improved. The epidemiological transition takes place when there are changes in specific demographic markers, notably, when a population’s life expectancy starts to increase and mortality rate starts a permanent decline (Omram 1971). Figure 1.10 shows patterns of stature change in a sample of Western countries from 1790 to 1930, after Treme and Craig (2013). From this graph the mentioned decrease in heights in Europe and also the US is evident, as is the continuous secular increase in the heights of many European populations after the late 19th century. Secular trends in stature in Finland and neighbouring countries will be discussed in Chapter 2. The following pages discuss the skeletal collection I have used in detail, as well as the social history of 19th century Finland.
52
Figure 1.10 Secular change in stature in selected Western countries from 1790-1930, after Treme and Craig (2013)