One of the year's most popular posts examined the evolutionary pull of running and high-aerobic activities on our brains. Above, a man runs past the Sydney Harbour Bridge in April.
Ryan Pierse/Getty Images
Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006.
Mosquitoes like this one can carry the virus that causes dengue fever, which may become a bigger problem in some regions as biodiversity is lost.
James Gathany/CDC Public Health Image Library
Photographer Freya Najade journeys into the weird sci-fi world of Europe's agricultural production. In one cow-milking facility she visited, "two people are needed to milk twice a day 300 cows," she writes.