Intended for healthcare professionals

Observations Only Connect

The anthroposphere is changing

BMJ 2009; 338 doi: (Published 15 April 2009) Cite this as: BMJ 2009;338:b1534
  1. Nicholas A Christakis, professor of medical sociology, Harvard Medical School, and attending physician, Mt Auburn Hospital, Cambridge, Massachusetts
  1. christak{at}

    Men already outnumber women but sex ratios are set to get even more uneven. Nicholas Christakis considers the perils of our changing population

    The human population is undergoing a rapid and inexorable demographic change in ways that will affect medicine and public health. I do not mean that our numbers are exploding—a topic that has been attracting attention since Malthus. Nor do I mean that life expectancy is rising—a fact that is widely appreciated. I mean a very modern and massive set of changes in the composition of the human population.

    Changes in four aspects of population structure are key: sex ratio, age structure, kinship systems, and income distribution.

    Sex ratios are becoming increasingly unbalanced in many parts of the world, especially in China and India (which account for 37% of the global population). The usual sex ratio at birth is roughly 106 males for every 100 females, but it may at present be as high as 120 for young people in China, or as high as 111 in India. This shift may arise from preferential …

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