I don't have to go any further than how they look. Visually they're glaring, textbook "primitive African savage" stereotypes. It's obvious. All that's missing is the "mushmouf". Oh wait, look at their whole lower jaw. And the color of their skins. And the deep black shading. And the hair. And, oh, everything. Come on, really. This couldn't be more obvious. "Umgug?"
And part of that kind of stereotype WAS that they were less well-evolved than Westerners/whites. I'm not sure how that's a difference, in fact it makes it even worse.
Here's a test. Show this to an African-American friend and ask them if they think it's racist and if they're supposed to be black: