The gist of Wrangham's idea is that chimps and humans inherited their violent tendencies from a common ancestor. As such, they both have a similar predisposition for becoming murderers in similar scenarios. Specifically, when the aggressor thinks that the attack will be low risk. Chimps, for example, prefer to attack when they can ambush their prey. If the element of surprise is lost the attack is abandoned.
And that's about as far as the video goes. The claim seems reasonable. All our close relatives (except the bonobos) have a tendency towards violence, which would suggest that our common ancestor also had it. And that we inherited it from them. This idea has a name. It's a condensed version of "demonic ape hypothesis", of which Wrangham is a big proponent. He's published assorted papers on it in the past; and even a book by about it too.
However, it does all hinge on there being parallels between human and chimp violence. If they're very different, positing a common ancestor (or at least, a common ancestor that behaved the same way) becomes a lot less reasonable. The main parallel discussed in the video is the way we both favour one-sided conflict. The full version of the hypothesis has another big one: that the ultimate goal of this violence is to gain territory; as having more territory is extremely beneficial for both chimps and humans.
Both of these similarities have been contested by other researchers.
For instance, colonial records from the Andaman islands indicate that violence between the indigenous groups is rarely one sided. Raiding parties often have casualties of around 85%. Hardly the sign of the one-sided tactics seen in chimps. Although even that behaviour in chimps has been contested. Whilst chimpanzee violence is prevalent for a primate, it still only results in one death per 7 years at each site. Whilst these deaths do often stem from ambushes; the rarity has led some to question whether it can really be considered an evolved behaviour.
Returning to the Andamans; the indigenous population there also presents a challenge to the idea that it's all for territory. Because of the violence between groups, people avoid the borders of their range. This artificially shrinks their territory. On the other hand, some groups in the region are more peaceful. Thus they can happily exploit the entire range of their territory without fear of attack. As such, it should come as no surprise that the peaceful groups wind up being larger as they can gather more food.
Of course, Wrangham hasn't taken these critiques lying down. He's conducted surveys of violence in indigenous populations. This reveals that ambushing is the preferred technique; and often results in a one-sided conflict. However, this work only examined 11 groups; with a lot of the data coming from the folk memory of the groups involved. Hardly the most complete, or objective, work. The Andamans and their evenly distributed casualties are also conspicuously absent from this work.
As this back and forth shows, violence is a complex thing. On the other hand, the demonic ape hypothesis is rather simple. A nice little narrative with a handful of causes and parallels. I think it's ultimately too simple to explain why humans do sometimes become murderers.
Of course, that's not to say it has no factual basis (chimps do like to ambush after all). Or that violence has no evolved component. Simply that this simple idea (hahaha) doesn't have enough depth to explain why.
And if Wrangham disagrees with me I'll fight him over it.
