Gestures of humility in social mammals
Dogs and wolves draw in their tails and whine when they are inferior or
weaker than an attacking dog/wolf. Some predatory animals present their
unprotected throats to superior/stronger animals of the same species. As
far as I know, primates do not show such behavior, Humans blush when
they are ashamed, no other primate species does that. Turning pink is
regulated by the autonomic nervous system, but there is no explanation,
as far as I know, about its origin in evolution. It could be a gesture
of ritualized simulated exhaustion.