Evolution is a card game that allows you to create unique species and throw them out into the food chain to see if they can co-exist peacefully or eat their competitors as carnivores.  Bottom line is, the more you eat, the more victory points you score, and the less you eat, the more you go extinct.  Everybody secretly throws some food into the watering hole at the beginning of a round.  Then you play your cards to add traits to your species, such as Pack Hunting, Horns, Hard Shell, and Long Neck.  Each of your species can have three traits at once, creating unique combinations that could have a tree climbing, horned carnivore coexisting with a hard-shelled, long-necked vegetarian with unstable DNA.  The traits in Evolution interact both obviously and subtly to produce interesting results at feeding time between the different species.  In addition to adding traits to your species you also have to discard cards in order to increase body size and population or to start an additional species.  A carnivore can only eat a species with a smaller body size.  Certain traits reek havoc on this rule, however, like Pack Hunting and Defensive Herding.  Population determines how much you can eat and score per round.  After all players play or discard cards, a feeding round ensues.  At the end of feeding phase you get more trait cards and start a new turn.  You play until the deck is empty and then score victory points.
We have played this game numerous times, and it never ceases to amaze me how the theme is captured so well in Evolution.  You get the sense that if you don’t adapt to what other players are doing (evolving) you will find your species starving to death or being eaten.  Having a giant carnivore without Climbing try to eat a tiny tree climber is impossible.  But if that same carnivore has the Intelligence trait, you can discard a card at feeding time to cancel the tree climbing trait for a moment so you can take a chunk out of the little bugger.  Again, the game really shines in this regard.  I can imagine my smart carnivore shaking the tree so a few of those smug morsels fall out.  The art in the game (both first and second edition) is wonderful and evocative.  Also, each player gets a player aid card that shows all the types of traits in the game and their characteristics.  Each player aid card also contains a unique list of monikers that allow you to make up funny names for your creations based on their combination of traits.  This makes it a little sadder when they go extinct but more glorious when they are fat and well fed at the end of the game.  Evolution is great, because win or lose, you get the feeling that you created something that had a real place in the world, whether it got eaten right away, or evolved into a total bad-ass victory point eating machine to stand the test of time.