• handedness;
  • head turning;
  • early development;
  • genetic, biological and environmental factors

This paper reviews the earliest documented manual and postural asymmetries, in the fetus and during the first months of life. I attempt to analyze which genetic and/or environmental factors are likely to trigger each one, as well as its consequences for the other ones. I conclude that right-handedness is prevalent in all cultures because an intrinsic tendency toward right-handedness has many occasions to be reinforced, from the uterine to the perinatal environment and from the familial to the cultural environment. Finally, the combination of potential genetic factors—direct (motoric) or indirect (postural)—with varied biological and cultural environmental influences over various periods during development may explain the high variability of handedness in typical populations (as long as hand preference is not equated with the hand used for writing).