exploration
New Environments
Right now we've got all our eggs in One Basket
"So that when somebody else comes, after we beat the buggers, when somebody else comes here to defeat us, they’ll find we’ve already spread over a thousand worlds, we’re at peace with ourselves and impossible to destroy. Do you understand? I want to save mankind from self-destruction."
--Peter Wiggin in Ender's Game, by Orson Scott Card
Little Blue Marble, Big Black Space
We've all heard the old addage not to keep all of our eggs in one basket. The reasoning behind this advice, of course, is that should disaster strike your basket, you don't lose all your eggs. Pretty straightforward, right?
Right now, we (the human race) are not heeding our own advice in the matter. We're the proverbial eggs and Earth is the basket in which we are so precariously riding.
The situation
The human race is currently operating with a minimum level of redundancy--individual bodies provide a layer of separation, genetic variances further that separation, and we've altered our local habitats in various ways which also provide differences. Let me take a moment to explore these three concepts a bit deeper...
Bodies - Every person on this planet, with their unique, separate, autonomous body represents an individual unit of humanity. So long as one or more person remains alive and functional, the human race is survived. So, that's what, about six or seven billion points of failure?
Genetic Variances - In reality, two individuals do not represent nearly enough diversity to maintain a valid, functional gene pool, so that changes the odds a bit. In other words, the closer we get to zero (read: extinction), the less robust our race will be.
That said, we've currently got a pretty diverse gene pool going on. This is what I meant when I said that genetic diversity provide further insulation from threats--in this case, the threat being resisted would be biological (in the form of viruses (both natural and artificial) and genetic weaknesses).
Local Habitats - We've also taken to altering little corners of our environment to create ease, enhance safety, and otherwise suit our personal fancies. Now, granted, we don't always do such a good job of this, but as a concept, it can provide further insulation from threats (e.g. bomb shelters, structures on stilts to deal with flooding, flexible, earthquake resistant structures, etc.).
So far, sounds like we're doing pretty good, eh? I mean, there're literally billions of us running around, building better structures and combining our DNA into new bodies. The thing is, with the exception of using technology to enhance our environments, these traits are simply inherent--natural. We're not taking the initiative to hedge our collective bets.
Also, everything discussed so far happens at a single planetary scale or smaller. Hence, Little Blue Marble, Big Black Space.
Threats
From a global level threat scale and higher, humanity exists as a single target. One planet-wide disaster/attack could remove us from the universe, just like that.
Natural
I'd say the biggest natural threat would be the possibility of a large celestial body of some type colliding with our planet. We can see a lot of this stuff coming, but would we really be able to do anything about it in time?
Probably not.
Man-made
Now, here's where it starts to get really scary. For the first time in history, humans are beginning to develop technology which poses a potential threat to humanity as a whole (not to mention the other species we share the planet with).
These dangers to ourselves have, so far, manifested themselves as three major threats--global nuclear war, biological warfare, and population growth/resource management.
Solutions
Okay, enough with the gloom and doom already. What do we do about it? We expand.
Terrestrial Expansion
One of the easiest things to do is expand list the habitats we call home. Floating cities, and especially underwater cities provide us with another degree of separation (or another redundant point of failure if you prefer).
Extraterrestrial Expansion
This is the one we should probably be looking at. By having separate, autonomous, extraterrestrial human habitats, we effectively increase the number of targets and redundant points of human existance. This should probably have become a major focus as soon as we learned how to escape Earth's gravity, but for some reason we're dragging our feet.
Off-world expansion can take many forms, each having its own strengths and weaknesses--space stations, colonies on alternative planets and moons, and generational ships provide an array of different possibilities.
Each independent, self sustaining body of humans provides an extra 'basket' to carry some more 'eggs', to continue the metaphor.