It's an obvious fact of nature that organisms go extinct. This planet has been around for a little over four and a half billion years, and in that amount of time, billions of species have come into existence only to go the way of the dodo. It is the natural progression of things, and evolution as we know it wouldn't be possible without it. Most organisms go extinct for completely natural reasons - competition, climate change, and natural disasters, to name a few. It is extremely rare for a species to go unchanged for long, and even species that do are not invulnerable to the age-old pressures of speciation and extinction.
There is one species, however, that has built up a society that completely invalidates most of these pressures. H. sapiens is no longer vulnerable to the classic methods of competition and environmental pressure to a degree that could result in its extinction. We are virtually unchallenged at resource gathering, and our technology and adaptability minimizes negative environmental effects.
Even so, it is difficult to imagine a species that has only been around for 200,000 years to be immortal in this sense. It stands to reason that humanity, like every other species, will eventually meet its fate. It may be when the sun eventually grows large enough to stop supporting life - approximately 1.5 billion years down the road - or it may be something much sooner. This month's topic therefore is: What do you think is most likely to cause humanity's eventual extinction, and why?
As for me, I've had a hard time determining for certain what I think is most likely, but there are a few popular theories I think are not:
1) Global nuclear fallout: I have a hard time imagining that humanity could have a nuclear war so bad that it would cause the species' extinction. Even if there was a nuclear disaster that resulted in the collapse of much of the civilized world, there would still be countless pockets of more isolated societies that would not be touched even by fallout.
2) Destruction and over-consumption of resources: Again, I think it's possible that, worst-case scenario, humans use up enough of their resources to cause a pretty major population crunch, but I do not believe it's likely that such an over-consumption could result in total extinction. There is always going to be photosynthesis, and therefore there is always going to be the potential to create food (synthetically or not).
3) Contact of Earth with a large comet or asteroid: Unless it is something extremely large (unlikely), a comet or asteroid would, at worst, block out the sun with dust for a period of time. Once again, this is something that could potentially eliminate a good chunk of the species, but probably not cause an extinction. A fairly sizable sample of the species would be able to survive with supplies for many years without sunlight.
As for what I think is more likely, there are a few possibilities:
1) A widespread global pandemic: Unlikely, but possibly more likely than other options, is a rapidly-spreading and extremely contagious disease of sorts. However, it would have to be pretty specific to result in an extinction. With most types of disease, there would still be those proverbial isolated societies that make it through, but with the right amount of contagiousness and latent dormancy I do think it's possible for a disease to eventually reach all corners of the globe. This would also, of course, only be possible in the event of there being no possible cure or vaccine, which in the current state of rapidly improving biotechnology, seems more and more unlikely. On the other hand, though, the prevalence of antibiotics in food sources nowadays means that bacteria are more rapidly developing immunities. (Fyi, swine flu is probably not a good candidate for a possible extinction-level pandemic.)
2) Alien invasion: Hey, you never know.
3) 1.5 billion years later: Everything on the planet will eventually meet its end when the rising luminosity of the Sun will eliminate the biosphere. Unless, of course, humanity manages to make a swift exit from the planet beforehand and settle elsewhere - which I also think is fairly likely (hey, 1.5 is a long time to develop new technologies). Even if humanity does manage to escape the destruction of the Earth via the sun, there's no way we'll escape the eventual heat death of the universe!
So, what do YOU think?