Wow. nice analysis. I agree with a lot of what you are saying. You might be right that certain characteristics (increased respiratory systems) wont offer a reproductive advantage. But evolution works in many ways - not just natural selection. Over long periods of time who knows what would happen.

I agree that plants will mostly be selectively bred. However, I do think that plants and animals (if animals are brought to Mars) will follow a natural evolutionary path as well. For instance, bacteria and pathogens will exist and they will evolve naturally. As such, humans, animals, and plants will all have to adapt to the changing threat of pathogens. So though I certainly agree that plant evolution will mostly be influenced by humans, I still think that there will be a natural component as well. Seeds, algae's and things like that would likely escape into the atmosphere and spread throughout the planet over time.

You sound pretty knowledgeable on the subject and gave me a lot to think about. Thanks for the comment! I'm interested in hearing more of your thoughts.