[2] All geckos, except species in the family Eublepharidae lack eyelids; instead, the outer surface of the eyeball has a transparent membrane, the brille.

Since they cannot blink, species without eyelids generally lick their own brilles when they need to clear them of dust and dirt, in order to keep them clean and moist.

The gecko eye, therefore, modified its cone cells that increased in size into different types, both single and double.

[4] Many species are well known for their specialised toe pads, which enable them to grab and climb onto smooth and vertical surfaces, and even cross indoor ceilings with ease.

Geckos are well known to people who live in warm regions of the world, where several species make their home inside human habitations.

These, for example the house gecko, become part of the indoor menagerie and are often welcomed, as they feed on insect pests; including moths and mosquitoes.

[9] The smallest gecko, the Jaragua sphaero, is a mere 16 millimetres (0.63 inches) long, and was discovered in 2001 on a small island off the coast of Hispaniola.

[10] The Neo-Latin gekko and English 'gecko' stem from Indonesian-Malaysian gēkoq,[11] a Malay word borrowed from Javanese,[12] from tokek, which imitates the sounds that some species like Tokay gecko make.

[19][20] These van der Waals interactions involve no fluids; in theory, a boot made of synthetic setae would adhere as easily to the surface of the International Space Station as it would to a living-room wall, although adhesion varies with humidity.

[21][22] However, a 2014 study suggests that gecko adhesion is in fact mainly determined by electrostatic interaction (caused by contact electrification), not van der Waals or capillary forces.

Gecko adhesion is typically improved by higher humidity,[21][22][28][29][30] even on hydrophobic surfaces, yet is reduced under conditions of complete immersion in water.

Use of small van der Waals force requires very large surface areas; every square millimetre of a gecko's footpad contains about 14,000 hair-like setae.

[32] The setae of a typical mature 70-gram (2.5-ounce) gecko would be capable of supporting a weight of 133 kilograms (293 pounds):[33][34] each spatula could exert an adhesive force of 5 to 25 nN.

Recent studies[30][36] have moreover shown that the component of the surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers (up to 100 nm beneath the surface); taking that into account, the adhesive strength can be inferred.

Development effort is being put into these technologies, but manufacturing synthetic setae is not a trivial material design task.

[58] Madagascar day geckos engage in a mating ritual in which sexually mature males produce a waxy substance from pores on the back of their legs.

[60] Appropriate segregation during meiosis to form viable progeny is facilitated by the formation of bivalents made from copies of identical chromosomes.