Their big eyes meant that they devoted a larger part of their brain to seeing.

However, Pearce suggests that this came at a cost to their social world. Other parts of their brain would in turn have been smaller.

“Since Neanderthals evolved at higher latitudes and also have bigger bodies than modern humans, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking,” Pearce said at the time.