Q: I don't understand what you mean by 'evolve', can you explain it?
A: The explanation is long, so the answer gets its own page. Also, hi, I'm Disgustedorite! I'm one of the staff members and the oldest newbie.
In nature, evolution is the process by which living things change as a whole over time. Think apes becoming men, or dinosaurs becoming birds. On Sagan 4, we mimic that with art as our method of adding new, fitting species to the world that are based off of previous species.
For example, when I was still very new to the project, I saw this species, the Harnessback:
...and I decided I wanted to make another species based off of it. So, I made the Hearthead:
The Hearthead is similar to the Harnessback, but it's faster and has a stronger bite, and it has better eyesight. It's basically like a cheetah version of the Harnessback.
Q: That sounds really limiting, my idea is more different than that.
A: It might sound limiting on the surface, but evolution can be chained, and the changes can stack up. After I made Hearthead, I made another new species based off of it, Brighteyes:
Brighteyes also chases down small prey like Hearthead, but it jumps off of cliffs to do so and has long feathers on its legs so it can break its fall by "running" in mid-air. It also has even better eyesight than before, letting it see distant prey from its high vantage points.
And then I made another species based off of Brighteyes, the Interbiat:
...which turns that mid-air running into wing beats to fly. I basically turned the original Harnessback into an alien bird in only 3 steps. The only limit is how many species you're willing to make to get there!
Q: Do I have to make long lines like that?
A: No, you're free to just do one-offs--and maybe someone will like your one-off idea so much that they'll do something with it, too!
For example, OviraptorFan decided to make his own descendant of Brighteyes, the Vibrant Manestrider:
...which, instead of flying, sprints around the undergrowth using its improved eyesight to find fruit and small critters to eat! And it also has a colorful mane to attract mates. And I myself also like this species, and have my own idea for one based off of it that turns that mane into a peacock-like display.
You can go back and forth like that, or many different people can evolve a lineage in sequence. Who knows, maybe your one-off species will become the start of something greater!