High mortality makes small people shorter
22 September 2009, by Sara Coelho
Low life expectancy and disease during a century of colonial rule has made the small-bodied people from the Andaman Islands, also known as pygmies, become even smaller.
Anthropologist von Eickstedt in 1927, with small-bodied people of the Andaman Islands.
'Body size is one of the most important features of human populations because it's a powerful indicator of environmental conditions,' says lead author Dr Jay Stock from the University of Cambridge.
Stature is related to good health and food quality, and can be used as a gauge for a society's overall development. 'If people start getting smaller, that means that something has gone terribly wrong,' Stock says.
This is exactly what has happened to the small-bodied indigenous people of the Andaman Islands in the Bay of Bengal.
'The colonial history of the Andaman Islands is tragic but provides an opportunity to research the consequences of high mortality in human body size.'
Dr Jay Stock,
University of Cambridge
Together with Cambridge colleague Dr Andrea Migliano, Stock spent many months hunting for Andamanese body-size measurements in old publications, museums and archives. The pair looked for height records of three tribe groups: the Great Andamanese who were always friendly to the Europeans, the Onge who came into contact with outsiders in the 1920s and the Jarawa who remained hostile until the 1980s.
The different degrees of friendliness towards outsiders set the fate of these three tribal groups.
When the islands were first occupied by the British in the late 1880s, Great Andamanese males measured on average 148 cm tall (4 ft 10 inch) while women were slightly shorter. Over the next two decades, their life expectancy plummeted due to high mortality rates and exposure to measles, tuberculosis and other European diseases.
By the turn of the 20th century, their numbers had dropped to 600 people, about a tenth of the original population size. During the same period of time, the Andamanese became smaller: the average male in the 1920s was around 2 cm shorter than the men that first encountered the British. Between 1879 and 1986, periods of high mortality are followed by decreases in the height of Andaman Islanders.
Stock thinks that the high mortality rates in the Andaman Islands during the colonial period are related to the stature decrease. Overall low life expectancy influences the timing of life's events: if people don't live long, they start having children earlier.
'If mortality is high, energy is shifted towards early age reproduction and not growth.' And if growth is hampered, people do not get as tall as they would otherwise become.
The hostile tribes
The Onge's isolation until the 1920s protected them against infectious diseases until later but their average height also dropped during the decades following contact with outsiders. As colonial rule became more relaxed, life conditions improved and the Onge's mean stature increased.
The Jarawa are the tallest tribal group in the Andaman Islands, at about 155 cm tall (5 ft 1 inch). Data from the Jarawa is only very recent because the tribe was hostile until the late 1980s, during Indian rule. The report published last week in Curent Anthropology argues that their isolation kept high mortality in check and prevented a decrease in stature. 'I'm not surprised that the Jarawa are the tallest, because they had the most stable population,' says Stock.
'The colonial history of the Andaman Islands is tragic but provides an opportunity to research the consequences of high mortality in human body size,' says Stock. The different kind of relationships established between the Andaman people and the colonists 'led to differences in mortality among these tribes, which appears to have been a fundamental determinant of variation in body size,' he concludes.
J. T. Stock and A. B. Migliano. Stature, Mortality, and Life History among Indigenous Populations of the Andaman Islands, 1871-1986. Current Anthropology doi:10.1086/605429, October 2009.
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