It was interesting to see that a Doctor Logan brought up at the recently completed NewSpace 2010 conference that humans may not be able to live on the Moon, Mars or any other very different planet from Earth. I've long thought the same thing.
Spreading out into the Solar System -- and eventually farther -- is going to take quite a bit longer than the true space enthusiast seems prepared to admit -- and deal with.
When European explorers began exploring our planet, they met human beings wherever they went. OK, the humans were somewhat different from Europeans, but they were recognizably human. Peoples from different continents could even interbreed. The earlier expansion of humanity from a location in Africa happened before we had reliable histories so it is rather hard to know just how long it took.
Antarctica is about the only example of a land that did not have people when Europeans arrived. It was not even discovered until 1820. It was ignored for the rest of the 19th Century. Amundsen and Scott raced for the South Pole a century ago. We now have some established bases and some adventurous tourists. Remember -- Antartica is a part of Earth. We can breathe the air, the gravity is the same, radiation problems are pretty much the same. It is just a lot colder than, say, Washington, DC. We do not have anything like Zubrin's Martian fantasy or an O'Neill colony even in Antarctica. It is far easier to get people and things to Antarctica than it is to the Moon or Mars.
The voyages of exploration even hundreds of years ago involved large numbers of people away from home for long periods of time. In space the normal time on ISS is six months. A few people have stayed up longer. It hasn't been good for their health.
We have discovered some utility for space regarding communications and remote sensing. We can do that today. The old L5 idea may be a part of our future -- but a distant part, at least on the scale of a human life. With a large base in orbit we will be able to experiment in ways that are now impossible. We need to learn how to do things in space. That's why NASA reform is so important. The agency does need to develop a bottom up, democratic way of working and living. Yes, the old top down approach did put 12 men on the Moon. But that was really in the nature of a political stunt that did no more than hint at possibilities. It is not a very effective way of producing the kind of knowledge and development that moving out into space is going to need.