Sad songs, as Elton John so presciently suggested all the way back in 1984, say so much. Elton – or, more accurately, his lyricist Bernie Taupin – was clearly on to something: they have increasingly become the prevailing musical currency. Where once we revelled in the unambiguous joys of thrilling pop songs, we now prefer them as bleak and miserable as the average British summer.
This is no mere conjecture. Psychologists have, albeit in inverted commas, proved it. A study from the universities of Toronto and Berlin has concluded that songs have indeed become progressively sadder over the past 50 years, both in tempo and mood. Its analysis of the most popular 1,000 songs since 1965 has revealed that, with each passing decade, the biggest hits have become more lugubrious and reflective. In the 1960s, 85 per cent of songs were written in a major key; today it's just 42 per cent – and, of course, the more minor the key, the sadder it sounds. Meanwhile, today's average song speed is a listless 100 beats per minute compared with 116 five decades ago.
There is a reason for this, according to the report's co- author E Glenn Schellenberg. "People like to think they are smart," he suggests. "And unambiguously happy-sounding music has come, over time, to sound more like a cliché. People have come to appreciate sadness and ambiguity more. Life is more complicated, and they want the things that they consume as pleasure to be similarly complex."
What he means, essentially, is that The xx, who are a Mercury Prize-winning group of catastrophically somnambulant disposition, could only ever be selling records in 2012. It's been a seismic shift. Where the carefree days of the 1960s were accompanied by the exclamatory pop songs of The Beatles, the 1970s by Abba's life-affirming kitsch, and the 1980s by Wham!'s silly ebullience, such frippery has now officially gone into recession, replaced by, frankly, the doom and gloom merchants.
Take grunge, which in the 1990s killed the happy hedonism of heavy metal and replaced it with stomach-ulcered angst. Then, soon after, Radiohead removed the posturing from British rock altogether in favour of post-millennial tension, and a deliberate absence of melody. (And when The Darkness tried to put it back, we all laughed, quickly discarding them.)
Even dance music has been affected. Kanye West, hip hop's best advert for extrovert living and monomaniacal arrogance, delivered, in 2008, an album called 808s & Heartbreak in which he sounded all but suicidal. West recovered, but later collaborated with US folkie Bon Iver, a man who is to happiness what Night Nurse is to clubbers.
The virus has spread. One of the most celebrated artists of the year is Lana del Rey, an American beauty as melancholic as an octogenarian on her deathbed lamenting lost love. Coldplay have taken their maudlin anthems – the slower, the more effective – into stadiums worldwide. Adele has reinvented the power ballad. And how else to explain the preponderance of Damien Rice covers on The X Factor? TV talent shows are surely places for joyful plastic pop, not the navel-gazings of either Rice or, for that matter, Leonard Cohen, whose magisterial "Hallelujah" was 2008's X Factor winner Alexandra Burke's winning single.
But "Hallelujah" was chosen for good reason: the show's producers realised, like Professor Schellenberg, that we are all in the grip of our own existential crises these days, worried about our lives, the economy, the Premiership. And we want our inner pain articulated by those who do it better than we ever could – even on Saturday-night telly.
Of course, there will always be exceptions to the rule, and pop can still bring uncomplicated joy. The authors of the research cite Lady Gaga, for example, whose single "Born This Way", they say, "sounds fresh, recalling popular music from an earlier time".
And there are further anomalies to remind us that pop doesn't have to be exclusively morose. Take Psy, quite possibly the happiest South Korean who ever lived, and surely the only South Korean to score a UK top-three hit. His single "Gangnam Style" is a nonsensical global smash, a proper pop song that, in this current climate, is practically alone in shining a light at the end of a very long tunnel.
But, don't worry, Psy's a flash in the pan, clearly. Normal, glum service will be resumed shortly.