The instinct to form social hierarchies and pecking orders is in virtually all social species. In our long prehistory of hunting and gathering, we were egalitarian out of necessity, because we were struggling to survive with few advantages against animal predators and the shifting environmental conditions. Before civilization we had no means of storing up private possessions or of enforcing social hierarchies, so as a practical matter we lived in small egalitarian clans. I go into this more in the article linked below.
Boehm seems to argue that egalitarianism is implicitly hierarchical since the weak gang up on the strong. That's consistent with what I'm saying here, since our nature (brain) is internally conflicted; hence the divide between animalists/reactionaries and humanists/progressives.
The conservative's authoritarian and regressive impulses are too primitive to stop at the imposed egalitarianism of the Paleolithic period. Their surrender is to the older, more universal mammalian parts of the brain that look for signs of amoral dominance and submission.
You say we need evidence-based policies. Policies in what direction? To what end? That's where the existential choice must be made between animalism and humanism. Science and instrumental reason don't tell us how society should be organized or what we should be striving for. Once we choose our ideals, we can think about how to fulfill them, taking note of the evidence, empirical restrictions, and so forth. So your appeal to evidence-based policies is neither here nor there.
You think I'm indulging in so much overheated rhetoric, though. On the contrary, I'm laying bare the truth that's obscured by the cliches and conventions of the polarized political discourse.
I don't say liberals have transcended their animal nature, so that's a strawman. What the analysis implies is that liberals (humanists) aim consciously to do so, whereas conservatives are opposed to that attempt at transcendence. See, for example, transhumanism, which is precisely a liberal (secular humanistic) plan for transcending our animal nature.