After watching Episode Twelve of Cosmos, I started thinking about how the human species could possibly end. If youu look on the Internet, you’ll find a strange mix of realistic and what I might call fanciful ideas about human extinction. The fanciful ideas are certainly the most fun to think about, and some of them may be legitimate threats. But the odds that we’d predict one of these events seem low, and our chances of doing anything about them are lower still. So I’ll leave those very fun ideas to science fiction.

I also think many of the extinction scenarios have an element of a morality play to them. Most involve technology gone bad. We create a race of nanobots that destroy human flesh, or we set the atmosphere on fire with a horrible new weapon, or we genetically alter a pathogen, making it invincible. These have a Frankensteinian flavor to them, which makes me distrustful. Are they real dangers, or are they afraid-of-the-dark warnings about “that which is best left unknown”?

Once you cull away those (and again, there may be legitimate extinction dangers in there, but they are both difficult to predict and just about impossible to stop), I think there are three real, legitimate threats to the human species.

1) human-caused environmental collapse

2) non-human-caused environmental collapse

3) economic collapse

The important thing to realize is that extinction is the norm. Virtually every species that ever lived is now extinct. Not only that, but most branches on the tree of life don’t lead to other branches (new species), but instead end abruptly. The history of life is one of extinction of most species, speciation from just a few lucky survivors, followed by a new extinction. While it is possible that a small part of humanity could naturally evolve into something else, the odds are not in our favor.

I believe that our global civilization (not our intellect alone, but the product of that intellect) might just possibly make humans different. We might be able to avoid extinction, but only because we can work together with our enormous technical resources to dodge threats. Therefore, any event that wipes out our technology for a long period of time or forever essentially dooms our species to eventual extinction. We can’t survive an asteroid impact if we no longer have telescopes.

So to the list.

1) human-caused environmental change. There is no question that our technology affects the environment. Our emissions disrupt the climate, raising temperatures. Our fertilizers create dead zones in the oceans. Our fishing wipes out whole living communities. Our agriculture creates deserts where none were before.  I’m no climate expert, and can’t predict just what our actions will do to the planet’s climate. I think it’s clear, though, that our impacts so far are pretty dramatic, and the changes we continue to make are like playing with a loaded gun. Eventually it will go off. If the climate changes drastically, our technology could collapse. Small bands of disconnected humans become vulnerable. While the climate change itself probably won’t lead to extinction, once we lose our technology we’re no different from any other species that has become extinct in the history of the Earth. Extinction via this route is probably slow, but is still inevitable.

2) non-human-caused climate change. This could be slow, like number one, or much faster. The slow events would be, for instance, the return of the ice. There will be another ice age. When it comes it will disrupt our world. If our civilization collapses in the face of the ice, and we don’t recover it once the ice pulls back, we’re again sitting ducks for the next big change. But the slow changes aren’t the big dangers here. Instead, asteroid impacts, a nearby supernova or gamma ray burst, or some disruption in the power of the Sun are both quick and (right now) impossible to stop. Other big dangers include super volcanoes, or a gigantic release of methane or other poisonous gas. If we are to survive as a species, we need to protect ourselves from these dangers. They’re not likely to happen soon, but what is unthinkable in a hundred years is inevitable in a hundred million.

3) Economic collapse. We will one day run out of oil. That event could be enough to cause the world’s economy to fall apart. If the economy falls apart, then our civilization falls with it. Once again, we’re left with limited technology, and we become sitting ducks for the changes that are bound to come. Though the least sexy, this third option seems like the most likely. Economic collapse could lead to war, nuclear or otherwise, that could both help bring on number 1 or dig us even deeper into number 3. No economy, no civilization. No civilization, no chance of saving our species.

The interesting thing about the three scenarios is that they’re all linked. We can’t keep pouring poison into the Earth. Eventually our waste will come back on us. But we can’t stop burning fossil fuels today. The economic collapse would be horrible, too, and would lead to the same eventual extinction. We can’t just stop having technology, because it is only technology that has any chance of saving us from scenario 2. We need our technology, with all its inherent problems, because without it we are just as doomed as any other species. And yet our technology could be the very thing that leads to our downfall.

So what do we do? I think there are a few common sense things that make extinction still possible but perhaps less likely.

First is education. Maybe one of the biggest extinction dangers is our own denial. Religions might preach denial (God will provide). Environmental movements might preach it, too (the Earth will provide). Even non-skeptical scientific movements might preach it (technology will provide). I think we need a rational, skeptical, critical world view that questions all these ideas rigorously, that sees the world with a clear view of reality, that makes magical thinking a thing best left in the corner. There’s no evidence of God. The Earth will kill us if we let it. Technology cannot save us unless we use it to save us.

Second is birth control, freely available to everyone at all times. So many of our problems are those of too many people. But birth control itself isn’t enough. We need to prize every life, plan for every child, make sure every new member of our species comes in with the best possible chance to thrive. I think that means not just free birth control but (this is where I’ll lose most of you) mandatory birth control, mandatory until individuals prove they are ready and are committed to raising their children as precious and treasured individuals. Parenthood should be a priviledge, not a right.

Third (OK, here I lose even more of you) is a movement beyond the free market. The free market can’t sustain us. The free market can’t regulate environmental catastrophe. It can’t foresee the end of resources. It can’t stop sausage companies from using . . . well, you don’t want to know. Particularly in fields like energy production, we need to get away from profits and move toward sustainability. We need to invest in nuclear fusion and solar power. These two sources, both essentially unlimited, are the only legitimate replacements for fossil fuels. Neither are likely to be profitable any time soon, but if we wish to have the technology we will need to survive asteroid bombardment, deep space supernovas, the Yellowstone supervolcano, or even the death of the Sun, we need long-term, sustainable energy. Nuclear fusion (in the short term – we could do it now if we just committed the resources to it) and solar power (in the long term – the energy from the Sun so outweighs all other sources that we need to find a way to tap it) are our lifelines to the future.

Can we avoid extinction? I don’t know. But it’s something worth fighting for, don’t you think?