In a report to the Convention in June 1794, Abbé Grégoire estimated that at least six million French people knew no French at all, and as many again couldn't hold a conversation in it. Those who spoke it 'purely' numbered no more than three million, out of roughly 28 million inhabitants. His report's title was blunt: it called for 'annihilating the patois'. It took, among other things, compulsory schooling from the 1880s to change that.
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.