Not really. From the time of the cave paintings at Lubang Serij Saleh 40,000 years ago, as well as 10,000 years before that, up to the beginning of the Neolithic revolution 10,000 years ago, all evidence is humans lived rather peacefully. As is evidenced also by similar remaining bands over the past centuries until now. The Neolithic revolution and rise of surplus, class societies, warrior castes and such was the beginning of such things. And that only spread over the entire globe over the past 600 years.

How does this jive with the inland Papuan tribes in Papua New Guinea? They were quite isolated and from what I read they can be just as violent (of course, not on the scale of mechanized slaughter by moderns)

It depends on what you mean, as I did not argue that life for the average person in a traditional society was filled with violence.

What I argued is that whenever two competing groups came into contact, wanting the same land, the result was usually genocide (or one of the groups fled to another area, where they would have to fight those inhabitants), and as a result, when history records a new group "inhabiting" or "settling" a peace of land that is new to them, then that inhabitation is generally not peaceful, but genocidal in nature. Regardless of whether there is a written history to record the violence, we can have confidence that the violence did occur.

Now, given that modern humans have been around for 300,000 years at least (the date keeps being pushed back, since before the Moroccan discovery, it was thought to be 100,000 years), and have been swarming over the whole earth, that is a lot of violence and genocide, even though it was certainly possible to live a life of peace as well for a specific individual, since migrations weren't going on all the time in all places.