The heart beats in a mouse embryo grown with stem cells made from blood. Now the research that claimed a simple acid solution could be used to create those cells has been retracted. Courtesy of Haruko Obokata hide caption

itoggle caption Courtesy of Haruko Obokata

The CRISPR enzyme (green and red) binds to a stretch of double-stranded DNA (purple and red), preparing to snip out the faulty part. Illustration courtesy of Jennifer Doudna/UC Berkeley hide caption

itoggle caption Illustration courtesy of Jennifer Doudna/UC Berkeley

A high-resolution image of the molecular carrier that moves the botulinum toxin from the intestine into the bloodstream. The carrier (silver) creates gaps in the gut lining by grabbing the rope-like molecules (red ribbons) that tether one intestinal cell to the next. Rongsheng Jin, UC Irvine, and Min Dong, Harvard Medical School hide caption

itoggle caption Rongsheng Jin, UC Irvine, and Min Dong, Harvard Medical School

Made for a tight grip: The female penis of an insect species newly discovered in Brazil has spines on it. Courtesy of Current Biology, Yoshizawa et al. hide caption

itoggle caption Courtesy of Current Biology, Yoshizawa et al.

Kent Stephenson, a research participant at the University of Louisville's Kentucky Spinal Cord Injury Research Center, has his level of muscle activity and force measured by Katelyn Gurley. Courtesy of the University of Louisville hide caption

itoggle caption Courtesy of the University of Louisville

Cat Or Dog? Sure, you can easily tell the difference. But a machine may not be able to guess on the first try. iStockphoto hide caption

itoggle caption iStockphoto

New research finds a close connection between the flu that devastated the horse population in North America in the 1870s and the avian flu of that period. Hulton Archive/Getty Images hide caption

itoggle caption Hulton Archive/Getty Images

The brain edits memories of the past, updating them with new information. Scientists say this may help us function better in the present. But don't throw those photos away. iStockphoto hide caption

itoggle caption iStockphoto

A mouse embryo grows from stem cells made by stressing blood cells with acid. The blood cells are tagged with a protein that creates green light. Courtesy of Haruko Obokata hide caption

itoggle caption Courtesy of Haruko Obokata

The sexually transmitted cancer is common in street dogs around the world. Noel Celis/AFP/Getty Images hide caption

itoggle caption Noel Celis/AFP/Getty Images

The superglue developed by scientists sticks to wet, bloody surfaces. Researchers hope the adhesive could one day seal a torn vessels or fix heart defects. Randal McKenzie / McKenzie Illustrations. hide caption

itoggle caption Randal McKenzie / McKenzie Illustrations.

There's data to support the notion that pot, or a drug based on its active ingredient, could help ease the fears of PTSD. Ted S. Warren/AP hide caption

itoggle caption Ted S. Warren/AP

Research excavations like these in Siberia's Denisova Cave are yielding clues to the mating choices of early hominids. Bence Viola/Nature hide caption

itoggle caption Bence Viola/Nature

Yes, you could do this at home. Growing bacteria you find in a pile of dirt or a local pond might reveal the next big antibiotic. Charlotte Raymond/Science Source hide caption

itoggle caption Charlotte Raymond/Science Source

President Obama walks into an auditorium in the Eisenhower Executive Office Building Monday for a speech about World AIDS Day. Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP

Lefties don't necessarily do everything with their left hand, and the ones who do might not use the right side of their brain for language. iStockphoto hide caption

itoggle caption iStockphoto