What forces enable a gecko to climb up a vertical surfaces?

The thousands of small hairs or "setae" found on the pads of their feet have the unique ability to adhere to surfaces without using sticky fluids, suction, or the more usual tiny hooks (found on insect feet). Scientists are still studying the exact mechanisms involved, but have suggested electrostatic forces (Van der Waals) or capillary action as likely explanations. Geckos are able to adhere to almost any surface.