The game supports up to five players (original game) or four players (newer edition), each of whom can have up to four species in play. Each species is either a predator or an herbivore, and players place representatives of their species on a board whose food sources and hostile terrain elements are in flux. Species can acquire traits like armor, anti-armor (sharp teeth), marine (able to swim), nocturnal, speed, and others. Predators need to keep up with their prey -- if the herbivore you're depending on develops speed, you need to as well or you'll need another food source. If two species want the same resource, it's time to fight it out.
The game mechanics between version 1 and version 2 are rather different from each other.