What triggers handedness? Genetics can play a part. Estimated inheritability of handedness may be about twenty-five percent. This may be reflected in left-handers who have a first-degree relative who is also left-handed. Identical twins may have differing dominant hand preference, especially if they are ‘mirror twins’. Epigenetics can play a part, as well. A weak association between ultrasound screenings during pregnancy and non-right-handedness has been found. Many children who were innately left-handed have been forced to use their right hand as their dominant hand, sometimes by having their left hand tied to their belt behind their back. Negative consequences can accrue from forcing the brain to operate differently from its innate preference. Meaning that the left hemisphere is wired to orchestrate muscle movements in a person who is right-handed. The right hemisphere directs muscle movements in a person who is left-handed. Preventing a person from using their innate dominant hand does not, apparently, change this brain design; it just makes it more energy-intensive to develop skills in their nondominant hand. More tomorrow.