By 600 million years ago we’re finding people who don’t fit comfortably into Homo erectus. A jawbone from around this time was unearthed in Germany, near Heidelberg, in 1907, and is sometimes assigned to a new species, Homo heidelbergensis. Another find from the same period, often assigned to the same species, comes from Bodo, Ethiopia.
This guy clearly isn’t modern Homo sapiens, but his brain is starting to get out of the Homo erectus range, and his browridge is a double arch, rather than an erectus-style straight bar. He’s also got cut marks on skull and face, from someone “defleshing” him.
For a long time, we could tell a story about how Homo heidelbergensis was the ancestor to both modern humans and Neanderthals, but the latest DNA calibration suggests the split may go back earlier. We’re not really sure that all the specimens assigned to heidelbergensis really were one species.