sinistrality

Sinistrality is the quality or state of being sinistral, meaning left-handed or oriented to the left. The term comes from Latin sinister meaning left. It is used in several scientific and general contexts to describe a preference, orientation, or morphologic trait that is left-facing, with the opposite term dextrality or dextral for right-facing.

In humans, sinistrality most often refers to left-handedness, the preference for using the left hand in tasks such as writing or throwing. Left-handedness is observed in about 10 to 12 percent of the population and is influenced by genetic, developmental, and cultural factors. The term sinistrality is largely technical; most literature uses left-handedness.

In biology, sinistrality commonly describes the direction of shell coiling in gastropods. Most snail shells coil dextrally (to the right); a minority coil sinistrally (to the left). Sinistral shells can affect mating compatibility and survival, and they have been of historical interest in evolution and population genetics. The left-coiling trait occurs in various land and freshwater snails, including some species in the genus Amphidromus, among others.

In anatomy and embryology, sinistral can describe structures that lie on the left side or that display leftward asymmetry, but the term is less widely used outside specialized fields. The term is generally paired with dextral to describe bilateral asymmetry or handedness.