The first song Human Nature ever sang together was Earth Angel by The Penguins.
That was back in November 1989, long before the days of the Australian band's hit single He Don't Love You.
Then they were just Sydney schoolmates, the only four guys in the choir.
"Andrew arranged Earth Angel for our end-of-year school concert after he saw it on Back to the Future, when Marty McFly plays it with the band at the prom," Phil Burton tells AAP.
The rest is history.
From there the Motown-inspired quartet formed The 4 Trax, before renaming themselves Human Nature in the `90s when Mike Tierney says they "jumped on the boy band bandwagon" along with the Backstreet Boys and 'N Sync.
A quarter-century later, the US-based vocal group are singing Earth Angel again.
Leaving the classic `50s track out of their 11th studio album simply wasn't an option.
Jukebox, their latest offering, is a compilation of covers of hits from the `50s and `60s including Under The Boardwalk, Unchained Melody, Wonderful World, Stand By Me and Twist and Shout.
"That era of music was sort of the basis of pop music in a sense," bass singer Toby Allen says.
"So many amazing songs are born from those eras."
There's only one original song on the album (End of Days, written by Andrew Tierney) but Human Nature's harmonising adds a unique touch to the classics.
The group have been based in Las Vegas since 2009, spending more than three years at the Imperial Palace and then moving to a residency at The Venetian in January to perform Human Nature: The Motown Show.
Their current musical flavour is almost unrecognisable against their earlier power pop days when they frequented the Australian and international charts.
Approaching their 25-year anniversary, they're comfortable with their own evolution, and no longer feel the need to follow any trends.
"We've been through lots of different phases in our career. I don't think we ever like to stay doing just the same thing for too long," Burton says.
"For us the Motown stuff and the Jukebox record is kind of going back to our roots and revisiting it, because Motown was some of the first music that we ever performed - that classic doo-wop stuff was what we did when we got together.
"We've developed enough over the years that we can go back to the past in a confident manner."
- Tickets to Human Nature's 2015 The Jukebox Tour - A 25th Anniversary Celebration go on sale on October 31.