Cranium 5, a skull found at Sima de los Huesos and thought to be either a late Homo heidelbergensis or an early Neanderthal. (Credit: Rept0n1x/Wikimedia Commons)

There’s a murky chapter in human evolution, one that occurs right before our species entered the scene.

Over 1 million years ago our ancestors belonged to the primitive-looking species Homo erectus. Jump to 300,000 years ago and Earth is home to at least three lineages of big-brained humans: Homo sapiens, Neanderthals and Deniso