What would be the evolutionary reason for blushing?

I saw someone embarrassed today (in a fun way) and he blushed (face turned red). Interesting and strange biological/physiological reaction. Any theories as to why this occurs?What would be the evolutionary reason for blushing?
Normal response to stress.





Under stress, the body pumps more blood to the head, to provide the brain with the oxygen, nutrients and hormones it needs to negotiate the ';dangerous situation.'; On some people, this rush of blood to the head appears as blushing.





Suspect this person also has a red face after jogging/sprinting/playing sports.





While an embarrassing situation poses no physical danger, the stress response still appears -- probably due to the awareness of the loss of social capital.





As far as evolutionary reason, one can only presume that individuals that exhibited an obvious blushing response to sexual advances increased the success of those advances.What would be the evolutionary reason for blushing?
I would guess that facial expressions would mean a big deal when communicating throughout social life. Blood is pumped more into the face probably to provide the facial muscles and tissues with more nutrients and oxygen to make humans able to express more easily in embarrassing situations.

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