From a scientific perspective, there is nothing natural about a 12-hour cycle. The Earth rotates once on its axis in about 24 hours (which is 12 hours of day and 12 hours of night). We could easily have chosen to split this rotation into 10 hours, 100 hours, or any other number. The choice of 12 is human-made, though it does match up nicely with the 12 cycles of the moon we see in a year.