Stress and Crabbiness

I got a good look at the relationship between stress and crabbiness yesterday for Aidan’s first day of Kindergarten. It was easy to see Aidan’s anxiety being manifested as difficulty picking out clothes. When I suggested a certain shirt (a nice collared polo shirt), he DID NOT want to wear that one. Of course, he ended up picking that one when given a choice of 5 nice shirts. I saw other similar reactions to what would usually be easy choices and routines that morning. What was more interesting was noticing my own stress and my wife’s resulting in exactly the same pattern. So I noticed a much greater than usual reaction when my wife did not hang up her used towel and did not turn on the bathroom fan (my pet peeves, that I trying to let go of and did not mention even though I dearly wanted to.) Any she was expressing some her pet peeves as well. So the way stress was manifesting was clear. What I wondered is: why is this way of letting out stress functional or is it? It seems like it would be more functional to let go of the small stuff under stress from an evolutionary standpoint.