It's pretty much like monkeys invading and killing the next
tribe of monkeys if they think they can get away with it. We
really haven't evolved very far in the direction in which we like
to think we've evolved. The bible is full of killing off neighboring
tribes, of course. Jehovah even commands it, as I recall.
Haidt uses the metaphor of an elephant and a rider to
describe humans. The elephant is in charge. The rider just
provides justification for what the elephant (which I associate
with "desire" - close to what Haidt was saying, I think) wants
to do, plus some planning and scheming I guess. Haidt
picked an elephant rather than a horse specifically to
symbolize the relative strength of the two components.
Haidt also mentions that Hume wrote, approximately, that
"reason is always in the service of emotions, and should be."
That's the opposite of the Socratic/Platonic idea of the mind
being the summit of man's condition. I'd agree with Haidt
that Hume is right. The rider would not be able to decide to
do anything were it not for the emotions of the elephant which
give him a sense of "purpose", however chimerical. It's like
Brahman's early mistake, making the first humans perfect,
but all they did was sit under a tree near the river and
contemplate the infinite. He corrected that mistake with his
second batch of humans, filling their minds with desires, to
make them get busy and do something more interesting.
(That bit about Brahman is not in the Haidt.) I need to read
another book, so I can stop talking about that one.