Interesting!!!
Easy to conclude from this study that: Inequality is inherent to any society. It's in the DNA for groups to give 2-3 wives to the big men who have a lot of children and to leave the others childless: this is natural selection, like we observe in groups of wolves, lions etc.
We need to compare this study with Scandinavia where inequality is at its lowest in the world and see what factors have made Scandinavia what it is today. From some TV programs like "Vikings" that enact some components of history - some - we see that only 500 years ago, Scandinavia was more like the tribes of the study. It means that a fundamental change happened quickly, during a few centuries only.