|A big blusher.|
The answer is simple: acceptance comes to those who blush. Think about it. When we're with a new group of people and we blush, we reveal something about ourselves. This lets the group know we're "one of them". In essence, blushing is a way to share personal values with observers. And there's no way to fake a blush so the observer gains here too. It's so weird: it's a communication tool, albeit one that is often embarrassing.
Blushing confers a direct evolutionary advantage on the blusher: group acceptance. Without that, early man would not have thrived. Nothing in life exists unless there's a good reason for it. Evolution is totally cool.
Here's a link to an article about the evolutionary aspects of blushing. I think this is a very cool science fact.