Here's a wildly unexpected proposal that just popped into my brain: Humanity should intentionally contaminate Mars with Earth lifeforms -- as soon as possible! The benefits vastly outweigh any concerns to the contrary. Indeed, it may be the smartest thing our species ever does.
The first obvious benefit is that it will get Earth life off of Earth, making it more likely that it will survive. Humans are wrecking Earth -- but even if we don't Nature may do it for us. All it would take is one big comet or meteor impact -- or a supervolcano or ice-age and much of the living systems and civilization we currently take for granted would vanish in the blink of an eye. Our only insurance is to have a "planetary backup" -- so why not use Mars? We back up our data -- why not our DNA -- why not also backup the amazing ecosystems and living organisms that have evolved so painstakingly over aeons on Earth? By moving at least some of them to Mars we can at least rest assured that no matter what happens on Earth, life in our solar system will continue in other places. But that's just the beginning.
Another benefit of seeding Earth life on Mars is that we can jumpstart evolution on Mars by several million (or billion) years by seeding it with life from Earth. And then we can study how it evolves and adapts. Remember, many organisms contain in their DNA bits and pieces of lots of previous generations and species -- and as they adapt on Mars they could even eventually re-evolve lifeforms we have (or had) on Earth. Perhaps life on Mars will revert to adaptations that existing on Earth when our climate was harsher. But over time that could slowly transform the Mars climate, enabling life to catch up again, and evolve to "higher" forms. Eventually that could even create and spread living systems and ecosystems that humans can live off of, or live within at least. Yes it could take a very long time to evolve higher lifeforms on Mars if we start by just sending microorganisms, insects, landcrabs, lizards, etc, but it could happen given that the selective pressures on Mars are similar to those on Earth. On the other hand, life could go in a completely unanticipated direction -- that would be interesting too!
It's actually a fascinating and important scientific question worthy of funding and long-term study: given the same precursor lifeforms and similar or identical conditions, will life evolve along the same evolutionary course as it has on Earth? Will Mars get dinosaurs eventually, or even primates? And what about flora and fauna? If the Bush Administration wanted to propose A Really Bold Initiative what could be better than seeding life on another planet?
Hey NASA, are you listening? -- this idea is worth $100 billion in funding. We could learn more from seeding life on Mars and studying it as it adapts, spreads and evolves for the next several thousand years than almost anything else we could do with the space program. It will help us learn about ourselves, the cosmos, and ultimately about how species move to new worlds. It will even lay the groundwork for humans to eventually colonize Mars by starting to build a food-chain and life support web there. And seeding life on Mars would have a greater long-term benefit on humanity, and the solar system, than just about any other space or Earth-sciences research program we could embark on.