The bdelloid rotifer Philodina gregaria. Bdelloid rotifers are tiny invertebrates that reproduce asexually. Courtesy of Micrographia hide caption

itoggle caption Courtesy of Micrographia

An artist's rendition of two Sinosauropteryx dinosaurs, showing their short, bristle-like feathers along the midline of the head, neck, back and around the tail, forming irregular stripes. Chuang Zhao and Lida Xing hide caption

itoggle caption Chuang Zhao and Lida Xing

Tools like these ax heads from Vinelz, Switzerland, were used by Neolithic farmers and may have been part of their sex appeal to hunter-gatherer women. Sandstein via Wikimedia hide caption

itoggle caption Sandstein via Wikimedia

Researchers dyed sperm from each deer mouse a different color; in this case, red represents one male and green another. The sperm joined together with their own kind, as seen here, allowing them to swim faster than those that did not cluster together. Heidi Fisher hide caption

itoggle caption Heidi Fisher

White-rumped sandpiper chicks on northern Canada's Bylot Island. Laura McKinnon hide caption

itoggle caption Laura McKinnon

This decorative shell ornament, attributed to Neanderthals, shows signs of being painted with orange pigment. It's one of several examples of ornamentation that researchers have found in Spain, at sites that were used by Neanderthals as far back as 50,000 years ago. Courtesy of Joao Zilhao hide caption

itoggle caption Courtesy of Joao Zilhao

A two-dimensional representation of E8 symmetry, the type of symmetry exhibited by particles in the study. John Stembridge hide caption

itoggle caption John Stembridge

A view of the central region of the Milky Way galaxy. Dark matter accounts for over 70% of the mass of the Milky Way, but because dark matter is invisible, all we see when we look up in the sky is a small amount of stars, planets and gas. AP/NASA hide caption

itoggle caption AP/NASA

Our sense of time can be influenced by things like drinking coffee, or being on an adrenaline rush from an amusement park ride like this one at Dreamworld in Australia. Bradley Kanaris/Getty Images hide caption

itoggle caption Bradley Kanaris/Getty Images