Front Matter

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• Science and Culture: Solving a math problem to create art
  How and why one mathematician takes an artistic approach to the Traveling Salesman Problem. Image courtesy of Robert Bosch.

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• Inner Workings: Orbiting experiment may help decode the mysteries of rubbly asteroids
  Does the surface matter of asteroids exhibit the “Brazil nut effect,” sorting itself like mixed nuts in a can? Image courtesy of NASA/JPL-Caltech.

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• Science and Culture: Looking at a shared sky, through the lens of art
  Two major telescope projects demonstrate how modern astronomy can share fundamental questions with ancient cultures—even as it collides with their sensibilities. Image courtesy of Yamaji Art Centre.

PNAS in the News

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• Obstructed labor in humans
  A mathematical model of human obstetrics finds that weak selection for a large newborn, a narrow female pelvis, or both factors might account for the large number of cases in which newborn size and maternal pelvis dimensions result in obstructed labor.
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• Plant diet of early humans
  At the mid-Pleistocene archaeological site Gesher Benot Ya‘aqov, Israel, researchers found 780,000-year-old botanical remains of 55 food plant species that likely complemented a diet of aquatic and terrestrial animals, findings that suggest a varied plant diet, staple plant foods, and the use of fire in food processing.
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• Geoengineering without ozone loss
  Researchers report a solar geoengineering method based on the injection of calcite particles, rather than the more frequently suggested sulfuric acid, into the stratosphere to mitigate the effects of climate change, and suggest that this method might help cool the planet while simultaneously healing the ozone layer.
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