It seems that 70,000 years ago the global population of homo sapiens was reduced to less than 26,000. Apparently they teased out that bit of info through some genetic analysis. As humans were by then in Africa and across much of Eurasia, that means we were very sparse on the ground. All seven billion of us spring from remarkably small numbers of people. Indeed, it’s been suggested that as few as seventy individuals came across the Bering Strait land bridge to eventually people the entire western hemisphere. We’ve had more than seventy people in our pad at parties. I never thought of them as a genome before. Well, I did once and got my face slapped. But I digress.
A million or so years ago our antecessor species Homo erectus seems in the genetic analyses (if I knew how they do this I’d tell you) to have been reduced to less than a thousand individuals….and remained like that on the razor’s edge of extinction for maybe a hundred thousand years. Everything we are was dependent on a population the size of a very small town or a medium sized high school or the fans of failing rock band in a big, mostly empty concert hall. Somewhere in that tiny population was some of us, genetically. Whatever genetic factors helped members of that population survive a particularly brutal hundred thousand years of Darwinian natural selection (as other related human species went extinct) lies deep in our own genome. And when 70,000 years ago something happened globally that reduced Homo sapiens to less than 25,000 individuals, we survived while the last of Homo erectus died out, unable to survive what it had once survived for a hundred thousand years. No one ever said natural selection was fair. It’s anything but. The fossil record is full of species of humans and proto-humans no longer here. Fleshed out by talented artists, they gaze at us with all the pathos of a Rembrandt. You can sense their intelligence and emotions. Then you look at the skulls again, bare and ancient and hopelessly extinct. There but for quirks of fate, is us.
There are very few examples on planet in human history where human societies or civilizations completely vanished. Even in times of catastrophic change–creation of the Sahara, 90% fatal pandemics in Amazon, volcanic devastation–human beings have stayed, even if reduced from large scale societies to hunter gatherer bands. Society changes, civilizations collapse, but the species does not go extinct. Indeed, our very evolution has been achieved by dealing with continuous stress and change including population crashes to as few as one thousand or less individuals for the entire species for as long as 100,000 years. We survived, evolved and thrived under extraordinary pressures that would have driven most species–indeed all other hominid species–to extinction. We are extraordinarily adaptable and virtually everything about us is designed to allow us to survive under extremely stressful conditions. That’s why we are here and not a single other human species remains. Society, culture, civilization are all dispensable, it is our extended family that is the default unit that allows Homo sapiens to survive almost anywhere under any conditions. The point of this is that no matter how severe climate change is, no matter if civilization collapses and our numbers are reduced to 1/100,000,000th of today’s population, Homo sapiens will survive. It would take something much more drastic–a giant asteroid, perhaps, or a nuclear war involving thousand of warheads–to completely annihilate the species forever. Both of which are possible, of course. But we will survive even the worst case global warming. It will not be comfortable, the impact on nearly all the world’s ecosystems will be devastating, and it’s hard to imagine a more dystopian future, but it will be livable for just enough of us to keep the genome going.