An old foe

Natural History, March, 2008 by Stephan Reebs

The first early human species to migrate out of Africa, nearly 2 million years ago, was probably Homo erectus. Moving northward into temperate latitudes forced our relative to adapt to reduced sunlight--but when and how? Fossilized H. erectus skull bones bearing signs of disease, recently unearthed in Turkey, are helping to answer those questions.

Quarry workers discovered the fossils in travertine formed 500,000 years ago--but not before slicing the rock into tiles, thus preserving only thin cross sections of bone. John Kappelman of the University of Texas at Austin and five colleagues examined the skull fragments and discovered small indentations on the internal surface of one. The indentations' shape and location betrayed a case of tuberculosis of the meninges--the membranes surrounding the brain and spinal cord. (Tuberculosis, or TB, usually targets the lungs, but it can also attack other organs and can affect the growth of overlying bone.) The Turkish fossils thus represent the oldest known human case of TB.

Vitamin D, which is produced in skin exposed to ultraviolet light, appears to help the immune system fight the bacteria that cause TB. Kappelman speculates that the bones' original owner--probably a young man--had dark skin, which blocks UV rays. Away from sunny Africa, dark skin may have unduly hindered vitamin D production, exacerbating vulnerability to TB in some portion of the H. erectus population and eventually prompting selection for lighter skin. (American Journal of Physical Anthropology)