Over 19 years, a once rare song sang by sparrows in western Canada has spread across North America, replacing a traditional song along the way, according to new research.
The big picture: Birdsongs, like human languages, have dialects that can evolve, and birds and humans learn their languages in similar ways and timeframes.
Senility is becoming an overt line of attack for the first time in a modern U.S. presidential campaign.
Why it matters: As Americans live longer and work later into life and there's more awareness about the science of aging, we're also seeing politicians test the boundaries of electability. Biden is 77; Trump, now 74, already is the oldest person to assume the U.S. presidency.
