> Just to be contrary, is it not at all possible that such and such a feature "evolved" in all the relevant life forms at the same (more recent) time in respons

> Just to be contrary, is it not at all possible that such and such a feature "evolved" in all the relevant life forms at the same (more recent) time in response to changing external stimuli? Depends. Joints can independently evolve. Knees are unlikely. In other words, nothing is impossible. A structure that performs any given function could evolve independently even if it looks different. The exact same structure or molecule? Unless it's one of the simplest 'solutions' to a problem, it's very unlikely without a common ancestor. Even things that should have one solution - like eyes - can lead to many different structures. Like our "backwards" retina which is not shared with octopi.