I've always believed that people could sing before they learnt to talk, and that it's a more basic form of language.
...............................................

I imagine it won't be long before someone comes up with evidence that female mice sing too.

To hear the mouse squeaks, the researchers played them back at one-sixteenth of the recorded speed and dropped the pitch to reveal what sounds remarkably like birdsong, with a similar richness and diversity.

I'm looking forward to the mousesong records coming out. Preferably in time for Christmas.
....................................

But that bit about how singing "in mammals had been thought to be restricted to humans, whales and bats." I known the old libel about horses not singing, but what about cats? Or gibbons? Or wolves?