The feeling of existential loss was long thought to be uniquely human. But studies of coyotes, cockatoos and other creatures are prompting some scientists to reconsider.

© Loren Elliott for The New York Times

There are more than 1.5 million known zoological species on Earth, with at least as many enigmas. Here are our top 10.

© Craig Cordier/Alamy

The feeling of existential loss was long thought to be uniquely human. But studies of coyotes, cockatoos and other creatures are prompting some scientists to reconsider.

© Loren Elliott for The New York Times

There are more than 1.5 million known zoological species on Earth, with at least as many enigmas. Here are our top 10.

© Craig Cordier/Alamy

Models of the insect’s nervous system have been trained to solve a Rubik’s Cube, play video games and even parallel park a car.