While there are no completely independent instances of natural evolution on Earth, there are partially independent instances. Where major diversifications have occurred, isolated either by geography or epoch from other similar diversifications, we have the opportunity to observe whether evolution tends to take the same routes or is always quite different. We can compare the marsupial mammals of Australia to the placental mammals of the rest of the world, or the modern mammals to the reptiles of the age of dinosaurs, or the bird fauna of the Galapagos to the bird faunas of less isolated islands.
What we find again and again is an uncanny convergence between these isolated faunas. This suggests that there are fairly strong ecological attractors which evolution will tend to fill, more or less regardless of the developmental and physiological systems that are evolving. In this view, chance and history still play a role, in determining what kind of organism fills the array of ecological attractors (reptiles, mammals, birds, etc.), but the attractors themselves may be a property of the system and not as variable. Synthetic systems may also contain fairly well defined ecological forms which may be filled by a wide variety of specific kinds of organisms.
Given their evident importance in moving evolution, it is important to include ecological interactions in synthetic instantiations of life. It is encouraging to observe that in the Tierra model, ecological interactions, and the corresponding evolutionary races emerged spontaneously. It is possible that any medium into which evolution is inoculated will contain an array of ``ecological attractors'' into which evolution will easily flow.