A blood test developed by Harvard researchers checks for evidence of past infection with more than a thousand strains of virus, from about 200 virus families. The swine flu virus shown here, A/CA/4/09, rarely infects humans.
C. S. Goldsmith/CDC
One of these things is not like the other: A 3-D printed model of a beige cowbird egg stands out from its robin's egg nest mates, though their shape and heft are similar.
Ana Lopez/Courtesy of Mark Hauber
The most recent common ancestor of all today's snakes likely lived 120 million years ago. Scientists believe it used needle-like hooked teeth to grab rodent-like creatures that it then swallowed whole.
Julius Csotonyi/BMC Evolutionary Biology
The skull of a chicken embryo (left) has a recognizable beak. But when scientists block the expression of two particular genes, the embryo develops a rounded "snout" (center) that looks something like an alligator's skull (right).
Bhart-Anjan S. Bhullar