There has been quite a bit of recent interest to potential evolutionary responses to warming climate in terms of decreasing mean body size of animals (e.g. Millien et al 2006. Ecology Letters 9:853–869). However, as pointed out by EGRU research, much of these declines could actually reflect environmentally induced plastic stress responses, rather than genetic adaptation to warming climate (Gienapp et al 2008. Molecular Ecology 17:167-178; Teplitsky et al 2008. PNAS 105: 13492-13496).
Due to course of scanning literature, I stumbled on an curious paper by Komlos published in Historical Methods in 2004. The point of this paper was to provide an additional test to disentangle in between disease and general nutritional conditions as explanations for the well-documented decline in mean body size of humans in Europe in the late part of 1700 century.
Kolmos reasoning was that if the cause of this decline was diseases – which impair effective conversion of nutrients to growth – the declining trend in body size should be confined to humans, and not show up in the size domestic animals, such as horses, which do not share their diseases with humans. However, if the cause was general shortage of nutritional resources, both horses and humans should show parallel decline in body size.
Using a database of horses purchased by Fourth Austrian Dragoons Regiment between 1774 and 1820, Kolmos was able to establish that the mean size of the horses declined as a function time in the similar way as the human stature (e.g Hungarian soldiers: 3.1% decline in mean stature). Hence, the conclusion was that declining resource availability, rather than diseases, was the likely cause of human body decline in late 1700 century.
What I found interesting in these results was that the decline in mean body size of humans and horses coincide with period known as “Little Ice Age”. I guess this might strengthen someone’s hunch that much of the trends in mean body size in response to climatic variations reflect plasticity rather than adaptation.
Komlos J. (2004) The size of horses during the industrial revolution. Historical Methods 37:47-53.