Your dog is getting ready to take a nap: as he heads with sleepy eyes towards the soft blanket you have placed for him on the floor, he sniffs the area and then curiously starts turning around meaninglessly in circles. It may take three or four turns before he curls up and gets ready to snooze. The ritual takes place every time now and you have grown eager for a plausible explanation.
There may be several theories but one of the most valid ones comes from the belief that in the wild dogs turned around in circles in order to press down the tall grass so to make a comfortable bed. Today, therefore this instinct may well still be alive in our domesticated dogs, even though they may no longer sleep in grassy areas but have a soft blanket and pillows instead.
Another valid theory is that dogs may turn around in circles because in the wild canines used to dig and sleep in dens. Dens were underground areas where dogs used to sleep in and raise their puppies. Digging dirt up to create a comfy spot is still as of today common practice in dogs especially in the summer, when dogs dig up dirt to create a shallow and cool area to sleep in. Turning around in circles therefore may be a dog's instinctual trait with the primary purpose of creating ''den like impressions'' with its paws before falling asleep.
Some experts may on the other hand claim that dogs turn in circles to sniff the ground and check for the scent of enemies. Indeed, often dogs that turn around in circles will do so by keeping their head quite low to the ground as if carefully inspecting the sleeping place. Only once the area appears safe, the dog will therefore lay down and enjoy a well deserved sleep.
Among all these theories, I personally believe that the ''stepping on grass instinct'' is the most valid. Both my dogs, have slept on the tile floors all summer long and have never turned around in circles, until this winter when they were offered a comfy blanket. Both started this turning around behavior out of nowhere and they now seem to put a lot of effort in making their ''bed'' comfy each night.
Turning around before laying down is therefore part of the many ingrained instincts dogs may carry along from the wild. Often such behaviors cannot be stopped and will continue in dogs no matter what. No dog teaches another dog this behavior, but it is rather programmed in their mind and will occur regardless if they live indoors or outdoors.