I think it was Arthur C Clarke who suggested that the most potentially valuable outcome of space travel, particularly the creation of independent settlements on other worlds, was the breakup of humanity into separate, distinct communities. We are rapidly becoming homogenized on this planet, our cultures are merging into one single industrialized model, languages are disappearing, and we are shaking out into a global society where social strata in each country will be more different from one another than different nations are. In other words, with instant communications and cheap travel, an office worker in Japan will be more like an office worker in Iceland than either will be like a cop or a short-order cook in their own town. Geographical and cultural differences will become subordinate to economic and social class, not nation or tribe.

Communities in space will be so isolated from one another, and be forced into such a state of independence, that human beings will once again be forced to develop independent cultures, different ways of looking at reality, different social structures. Just as an animal species can be forced to evolve into separate species when populations are isolated on islands, or separated by geographical barriers, so will human cultures. Human colonies on other worlds will become very different from those of their home worlds. I believe this has a survival value. Different kinds of people in different places means we will be introducing variety into culture. We are more likely to produce ways of looking at reality, and our own communities. A variety of responses to human problems makes it less likely the entire species will be wiped out by any one aberration or decadence.

Space travel will guarantee the survival of the species not just because no one single catastrophe will be able to wipe us all out, but because we will branch out into a variety of distinct and unique civilizations capable of dealing with a variety of challenges. Natural selection demands random variation.

And to carry the evolutionary biology analogy one step further, when separated populations encounter (or conflict with) one another they will cross-fertilize--the cultural gene pool will mix, just as the genetic material is mixed in sexual selection. This model worked for organic life as it evolved into every environmental niche on the planet, and it worked for humanity as it spread out of Africa and conquered the world.

But we have no guarantee that this same model, no matter how appealing it may be, can be scaled up to support a human diaspora across the galaxy. There may be sociological as well as physical reasons why this form of expansion is not possible. And even if it is, it is only inevitable that other species and civilizations will also be doing the same thing, and sooner or later our expanding sphere of influence will collide with theirs.