Sour may be the oldest taste

What does danger taste like? Around 500 million years ago in the deep ocean, danger tasted sour. Very sour. Fish evolved the ability to taste acidity in water which can be harmful for the animals.

But as this PBS Eons video explains, "In a few animal groups, including us, its role has reversed. The taste of danger became something it was dangerous for us to avoid."

image: AlexChGraphics/