@mig
Standardized behavior.
You have 2 options. Left and right. Maybe by accident, 51 percent of cases people decided to dodge to the right. When they did so successfully, their brain noticed that it was working better.
51 percent became 52...53... 80... 90
and now, from something that was a cointoss became a solved problem.
@LukeAlmighty yes, I think there is a right-left-handedness at the beginning and as a result it synchronises, so then left-handers do it too (but I don't know anyone who did this "research" as well :-))