The squirrels are the new dominate species of the known Earth. Skwerls come from piles of excess dryer lint. When these piles reach a certain weight they attain critical mass, and thus a skwerl is born. Skwerls are, of course, fungal. The absurdity of this placement is obvious to anyone with a backyard.
Adults form sporangia under the cute bushy tails and leave the spore everywhere.
This is also the reason they are so difficult to eradicate. As anyone who has experienced a fungal infection can tell you, the cure is often elusive, and the infestation persistant. My theory is that Squirrels evolved from the squirrelissimo latino, as did their close relatives, the chipmunks. There is no theory. They were creted by God on the sixth day.