In the 18th and 19th centuries, hereditary deafness was common on Martha's Vineyard, off Massachusetts: in some villages, about one person in 25 was deaf. As a result, hearing islanders signed too, every day. Deafness there was hardly a social barrier. The island's sign language died out in the mid-20th century.
In Kuşköy, a mountain village in northern Turkey, people talk across valleys by whistling Turkish. A 2015 study showed that whistled Turkish draws on both hemispheres fairly evenly, whereas spoken Turkish relies mostly on the left. The physical form of the signal, it turns out, matters to the brain.
Speech has no gaps between words. In 1996, researchers played 8-month-old babies a continuous stream of made-up syllables for just two minutes. The infants picked out the 'words' by tracking which syllables tend to follow one another. That's probability calculation, done without a calculator or any visible effort.