The art and science of bird song and human speech: understanding their beautiful and expressive relationship. From the article:

The [Hmong] language is perhaps most beautifully expressed during a now rarely-performed act of courtship, when boys wander through the nearby villages at nightfall, whistling their favourite poems between the houses. If a girl responds, the couple then start a flirty dialogue. The couple may create their own personal code, adding nonsense syllables to confound eavesdroppers

It’s not just the enticing melodies that make it the perfect language of love. Compared with spoken conversations, it is hard to discern the identity of the couple from their whistles – offering some anonymity to the public exchange….

These mysterious languages demonstrate the brain’s astonishing capacity to decode information from new signals – with insights that are causing some neuroscientists to rethink the fundamental organisation of the brain. The research may even shed light on the emergence of language itself….

[Julien] Meyer has now identified whistled languages in every corner of the globe. Given that the whistles can travel much further than normal speech – as far as 8km (5 miles) in open conditions – they are most commonly found in mountains, where they help shepherds and farmers to pass messages down the valley….

Not only does this [research] demonstrate the brain’s flexibility; the results, published in 2015, might even help people rebuild their lives after a stroke. Damage to the left hemisphere can render someone unable to speak – but [Onur] Gunturkun’s findings would suggest that they might still be able to shift their processing to the right hemisphere and talk in whistles instead. As he puts it: “There are many ways to Rome”. He emphasises that this was not the primary aim of the research, however. “It was just curiosity – for the sake of understanding the world around us.”…

Delve even further, and we might begin to understand how those traits arose in pre-history. Music and language both involved extraordinary changes: refined articulation, the capacity to imitate others and the ability think symbolically. But what set it all in motion?

One particularly elegant solution to this conundrum dates back to the father of evolutionary theory, Charles Darwin, who proposed that the two traits arose together as a kind of “musical protolanguage”. According to this view, humans first started singing before we could talk – perhaps as a kind of courtship ritual.