epidermis

"No one likes to lose hair, but when it comes down to survival in stressful times, repairing the epidermis takes precedence," says Fuchs.

It removes the epidermis and leaves the nerves exposed.

They expand clonally instead, aided by KIT ligand signals released from surrounding tissue and the epidermis.

Butts are, after all, the indoor kids of the epidermis.

"We discovered at least two different stem cell populations -- one that regenerates tissues such as epidermis and neurons, and another that forms muscles and connective tissue," says Adelmann.