Final answer:
Geckos have tiny hairs on their feet called setae that branch into triangular tips called spatulae, which provide an extensive surface area. This surface area allows geckos to stick to surfaces through weak intermolecular attractions known as van der Waals forces. Geckos can control their stickiness.
Step-by-step explanation:
Geckos have an extensive surface area on their feet due to the presence of hundreds of thousands of tiny hairs called setae that branch into triangular tips called spatulae. These spatulae provide a large total surface area for the gecko to stick to surfaces through weak intermolecular attractions known as van der Waals forces. The total attraction over millions of spatulae is strong enough to support many times the gecko's weight.
By changing the angle between their spatulae and the surface, geckos can turn their stickiness 'on' and 'off,' allowing them to easily transition between sticking and unsticking from a surface. This ability is achieved by curling and uncurling their toes, which alters the contact between their spatulae and the surface. Further research on geckos' adhesion mechanisms may lead to the development of better adhesives and other applications in various fields.