I am not sure where you are going with your point about human nature.
Avarice, greed, jealousy, anger, violence, and desire for power all seem to me to be at the ready in human development as much as are generosity, lovingkindness, empathy, and desire to serve others. I believe it can readily be argued that these two kinds of traits are equipotential within us. You may be ready to argue that cultural evolution gone awry has nurtured these less desirable traits, but that would not take away from the argument of equipotentiality. Yes, the ik and the pygmies we read about so long ago developed opposing traits due to the differences in natural resources within their niches, and for whatever reason that I don't remember, the Ik could not expand their territory. Jealousy or avarice can aid the survival of the individual and therefore the species. (And it is the survival of species rather than individual that evolution selects for). So there is not really a need to selects against jealousy, greed, except for the nurturance of the young and family life of course.
About human nature:
First, what I will be showing in the next installment does not make claims about what human nature is. Rather, what I claim to pretty well prove is that the history of civilization manifests a destructiveness and an ugliness that would be there regardless of human nature. I will try to show that any species that crossed that threshold -- extricating itself from the niche in which it evolved into "inventing its own way of life" -- would inevitably trace a similarly destructive and ugly course.
That being said"
Clearly, human beings have the "potential" to be avaricious, violent, lusting for power, and all those other ugly things. If we did not, humans would not have been capable of doing what history shows greedy and power-hungry people doing.
But I don't know if there's any reason to assume that the worst of our potentials are of equal potential to the best ("equipotentiality," you call it).
I know that you are deeply familiar with Harlow's studies of the rhesus monkey infants raised without mothers but either with terry-cloth-covered fake mothers or merely wire fake mothers. The one's who got nothing warm and cuddly at all grew up to be completely maladjusted, whereas the ones that got terry-cloth -- though they must have been rather less well nurtured than infants that had real mothering from their real mothers -- were a lot better off.
We would not conclude that the monkeys' potential to be like the wire-raised monkeys was equal to their potential of being sufficiently well adjusted to have normal social interactions with other monkeys and to engage in normal mating behavior when adult, would we? The rhesus infant is born with a reasonable expectation to be in the highly probable rhesus situation, not the warped circumstance that Harlow constructed for them.
Similarly with the Ik and the Pygmies. As I recall, it turned out that the tribe called the Ik were studied at an extremely abnormal state in their tribal history: their society and their way of life had been pretty much devastated, the social order had almost completely broken down. And it was in that circumstance that they showed a number of pathological social behaviors, like complete amorality.
There is pathology and there is health. Evolution favors health, but does not guarantee it.
But just as a rhesus monkey is more likely to develop into a normal monkey from a normal upbringing, and be helped to become a fully functional member of a rhesus group, so also with us human animals. Over the hundreds of thousands (and before that, millions) of years of our evolution, our kind has generally been born into social groups that were reasonably functional. Those that weren't would likely disappear from the gene pool. And I believe that the Ik were well on the way to collective disappearance at the time they were studied.
We can become like the Ik, but only under abnormal circumstances. And so that outcome, I would argue, is not rightly seen as "equipotential."
What the parable of the tribes shows is that a new evolutionary process arose -- not dictated by human nature -- that created a warped, evolutionarily abnormal social environment for human beings to grow up in. It describes how and why this second social-evolutionary force that has been, in many ways, hostile to the human nature shaped by the biological-evolutionary force that instilled our basic needs and tendencies.