Cyrtophora citricola, a type of orb-weaving spider, live in big colonies. So males potentially have a large pool of females from which to choose a mate. Buschwerk/Flickr hide caption

The four cuts at the top of this skull "are clear chops to the forehead," says Smithsonian forensic anthropologist Douglas Owsley. Based on forensic evidence, researchers think the blows were made after the person died. Donald E. Hurlbert/Smithsonian hide caption