Romansh: I simply cannot see how an asteroid crashing into the earth can be called Natural Selection. > > For me natural selection and the environment are inseparable. > > Asteroids are major step changes in the environment, > > and evolution could be considered an incremental change, ie the flora and fauna within an ecosystem change slowly. A biological entity shapes its environment (not intentionally)and that environment in turn shapes the entity's evolution.-The problem is interpreting and defining where in a time sequence does natural selection take place. I agree that an asteroid is part of a process of various changes that can end up challenging survival. As I see it, there must be changes in competition and in environment, then adaptations, and then finally as a result of competition, survival of some phenotypes. I view natural selection only as the competition/survival part of the process.