The Bottleneck

You are one of the last. Not one of the last of your village, or your tribe — one of the last human beings alive on Earth. The fires in the sky have gone quiet now, but the cold they dragged behind them is still here, folded into the soil, killing the plants the animals eat. Somewhere to the north, a mountain called Toba opened its chest and poured enough ash into the atmosphere to dim the sun for years. Maybe a decade. Maybe longer. We still argue about how long. What we don't argue about is this: when the smoke cleared, the genetic evidence suggests something like a thousand breeding humans remained. Perhaps two thousand. Not twenty thousand. Not a hundred thousand. A number small enough to fit inside a few city blocks. Every person alive today — eight billion of them, spread across every continent, speaking seven thousand languages, building cities and satellites and arguments — descended from that remnant. You can see it in your own DNA if you know where to look. Human genomes are suspiciously, almost embarrassingly alike. We are far less genetically diverse than a single troupe of wild chimpanzees in central Africa. That is what a bottleneck looks like from the inside, ten thousand generations later: everyone you will ever meet wearing the same narrow inheritance, carrying the survival of the same desperate few.