Keyboard history - Alternatively Sized Piano Keyboardssmallpianokeyboards.org/keyboard-history/
Piano keyboards used to have narrower keys. Today's keyboard size dates from the1880s, designed to suit concert venues and large-handed male virtuosos. + https://paskpiano.org/about/ via Saintloup
The Thumb Zone: Designing For Mobile Users — Smashing Magazinesmashingmagazine.com/2016/09/the-thumb-zone-designing-for-mobile-users/
If there is one thing that will stand the test of time, it’s thumb placement on mobile devices. This makes consideration of the "thumb zone", a term coined in Steven Hoober’s research, an important factor in the design and development of mobile interfaces.