Mortality leads to small stature

Stature, Mortality, and Life History among Indigenous Populations of the Andaman Islands, 1871-1986:

Despite considerable interest in the evolution of small body size, there is little evidence for changes in body size within smallâbodied human populations. This study combines anthropometric data from a number of studies of the body size of Andaman Islanders from 1871 to 1986. The colonial history of the Andaman Islands is characterized by high rates of mortality among the indigenous populations. However, longâterm conflicts between tribal groups of the Andaman Islands and British and Indian settlers led to some groups being relatively isolated and sheltered from infectious disease and the high rates of mortality that affected other groups. When temporal trends in stature are compared in this context, there is evidence for a reduction in stature among the Great Andamanese who had close contact with the British during the period of highest mortality. Adult stature among the Onge appears to have increased as government involvement diminished following Indian independence. The Jarawa, who had lower rates of mortality throughout the past century, have significantly higher stature than the other groups. These results are interpreted in the context of lifeâhistory theory, adaptation, and plasticity. They provide the first longâterm diachronic evidence for a relationship between mortality and stature among smallâbodied humans.

The differences among Andaman Islander groups is well known to me. What is novel is the idea that the mortality rates could be driving selection for earlier maturation, and so resulted in smaller stature. My own assumption was that morality is a consequence of illness which generates morbidity, and small stature is simply an outcome of that morbidity. After all, in Farewell to Alms Greg Clark reports data that populations which have been subject to recurrent plagues are wealthier and larger than those who have not. In this case, mortality and morbidity have been decoupled, and the "thinning out" of the population shifts it below the Malthusian limit and increases standard of living (the same was evident for some Native American groups in the wake of the Great Dying).

See ScienceDaily for more.

Citation: Stature, Mortality, and Life History among Indigenous Populations of the Andaman Islands, 1871-1986 J. T. Stock and A. B. Migliano, Current Anthropology 2009 50:5, 713-725, DOI: 10.1086/605429

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morality is a consequence of illness

Depends. If you get a really high fever you might, say, dream up some crazy religion.

Regarding the paper, it seems a bit counter-intuitive. I would have expected contact populations to have reduced selection on shorter stature and increase selection on greater stature. But that would have been just a guess on my part.