Each and every person of non-African descent carries traces of DNA derived from ancient hominin species to a varying extent.
"No result like this had ever been described anywhere in the animal kingdom," said study author Daisy Robinton.
Researchers link a supernova explosion 2.6 million years ago to the extinction of marine megafauna.
Twins are common in deer. Conjoined twins are not.
Scientists think the genetic mutation behind these teeth protected babies against an intense lack of sunlight.