​The changing of organisms with time.

​​evolution

​Catastrophic event that kills off many species.

​​mass extinction

​An inheritable change in an organism's genes.

​​mutation

​The mechanism for how living things might evolve with the passage of time.

​​natural selection

The formation of a new species.

​​speciation

​A group of interbreeding organisms that is reproductively isolated from all other forms of living things.

​​species