opinion:
As different as the Naldi homo species was from the Neanderthal, the Neanderthal was probably different from us. We may have viewed them as wildmen. 80% of Homo Sapiens possess the cooperative trait of empathy.
My hypothesis within the theory of Survival of the most cooperative is that Neanderthals were without empathy which made them by our definition psychopaths. Empathy is a nascent trait as is narcissistic psychopathy.
Prison populations contain over 30% psychopaths. Evolution may diminish that trait over time. Brain size is not the issue but the nature of the brain is most crucial. 20% of the current population are psychopaths may sound high but psychopaths in suits are a real problem. It is not an accident that Trump's base is also 20$.