Research with living systems is never simple, scientists say, so there are many possible sources of variation in any experiment, ranging from the animals and cells to the details of lab technique. Geoff Tompkinson/Science Photo Library/Getty Images hide caption

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Researchers Unravel Strange And Contradictory Feelings About Power

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Alex Reynolds/NPR

When The Brain Scrambles Names, It's Because You Love Them

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Spider Silk Is Stronger Than Steel — And Now It Can Be Made In A Lab

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The highly rated variety of medical marijuana known as "Blue Dream" was displayed among other strains at a cannabis farmers market in Los Angeles in 2014. Frederic J. Brown/AFP/Getty Images hide caption

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Marijuana's Health Effects? Top Scientists Weigh In

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For the first time, scientists have synthesized a three-stranded molecular braid that twisted into a knot with eight crossings, as in this rendering. Stuart Jantzen/Biocinematics.com/Science hide caption

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Stuart Jantzen/Biocinematics.com/Science

Scientists Have Twisted Molecules Into The Tightest Knot Ever

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New Gene-Editing Techniques Hold the Promise Of Altering The Fundamentals Of Life

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The killer whale J2, better known as "Granny," pokes her head out of the water in the Salish Sea near the San Juan Islands of Washington in July 2016. Granny, who was thought to be about 105 years old at the time, was presumed to have died later that year. Mark Malleson/Center for Whale Research/AP hide caption

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Mark Malleson/Center for Whale Research/AP

Menopause Mystery: Why Do Female Killer Whales Experience The Change Of Life?

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The hyolith Haplophrentis extends the tentacles of its feeding organ (lophophore) from between its shells. The paired spines, or "helens," are propping the animal up off the ocean floor. Danielle Dufault/(C) Royal Ontario Museum hide caption

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Danielle Dufault/(C) Royal Ontario Museum

Despite efforts to reduce pedestrian deaths, many cities have become more dangerous for walkers in recent years. Alessandro Scagliusi / EyeEm/Getty Images/EyeEm hide caption

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This 52-million-year-old fossilized tomatillo was found in Patagonia, Argentina, shedding light on the origin of nightshade plants. In this specimen, the slender stalk is preserved, and the former papery and lobed husk is broken at top to reveal the large, fleshy berry underneath — now turned to coal. Peter Wilf, Penn State University hide caption

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Peter Wilf, Penn State University

Dungeness crabs for sale at Fisherman's Wharf in San Francisco. California's Dungeness crab season was shut down in 2015, when record high ocean temperatures and lingering toxic algae blooms raised the domoic acid in shellfish to unsafe levels. A new study links dangerously high levels of the neurotoxin to warmer ocean temperatures, suggesting such closures could become more common in the future. Eric Risberg/AP hide caption

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Eric Risberg/AP

Humans Worry About Self-Driving Cars. Maybe It Should Be The Reverse

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