Animals

Jellyfish didn’t need novel genes to take an evolutionary leap in complexity.

A report that a fish can pass the “mirror test” for self-awareness reignites debates about how to define and measure that elusive quality.

How does evolution select the fittest “individuals” when they are ecosystems made up of hosts and their microbiomes? Biologist debate the need to revise theories.

For decades, researchers have commonly assumed that higher oxygen levels led to the sudden diversification of animal life 540 million years ago. But one iconoclast argues the opposite: that new animal behaviors raised oxygen levels and remade the environment.

An unlikely team offers a controversial hypothesis about what enabled animal life to get more complex during the Cambrian explosion.

Game theorists have developed a new model of communication among animals. It suggests evolution will produce a situation in which members of a species are honest most of the time, but not always.