Started on the Big Think article and it's already full of wrong information. Chimps do NOT regularly gang up on and kill males from other bands. Most of the time, they stick to the center of their territories in order to not actually encounter other animals. If a band finds a lone male from another troop, they probably will kill him, but it's not a regular or even common occurrence.
"In most cases, unless one group of chimps is vastly bigger and stronger than another, they never even get close to each other in the wild, but instead will pant-hoot at each other from afar. In fact, chimps rarely patrol the edges of their territory, preferring to keep more to the center, where they are less likely to encounter strangers. As is noted in Chimpanzees, Warfare, and the Invention of Peace, a chapter written by Michael L. Wilson, “Because aggression generally involves costs, animals usually avoid getting into direct fights if they can (Fry & Szala, chapter 23). Instead, they threaten and display at their rivals. If they do get into a direct fight, animals usually seem content to chase rivals off rather than pursuing, capturing, and killing them. Fatal fights may occur, however, when the value of the resource is particularly high, or when the fighters do not expect to live long, or when the cost of killing their opponent is low.” (p. 363)
I tried to read a bit more but it's just so full of unsupported horseshit that I just can't... Finding a couple of skulls that have been bashed in is NOT evidence of war. It's evidence of murder or execution, perhaps but it's not evidence of intentional, wide-spread, organized violence. And as noted in the other piece, most of those bashed in skulls were from before we ever encountered each other — so really not evidence of warfare with humans.
This kind of lazy, undereducated piece that just conflates all sorts of things and doesn’t really know what it’s talking about really pisses me off, but the other two links were highly informative and interesting.
