By Patrick Pester via LiveScience Headline Image Credit: Agustin Paullier/Contributor via Getty Images From all-out nuclear war to a giant asteroid strike, it's not hard to imagine ways human life on Earth could abruptly end. But assuming there are some survivors, how many people would it take to keep our species going? The short answer is, it depends. Different catastrophes would create different doomsday conditions for surviving human populations to endure. For example, a nuclear war could trigger a nuclear winter, with survivors facing freezing summer temperatures and global famine, not to mention radiation exposure. However, putting some of these conditions aside and focusing on population size, the minimum number is likely very small compared with the approximately 7.8 billion people alive today. "With populations in the low hundreds, you can probably survive for many centuries. And many small populations of that kind have survived for centuries and perhaps millennia," Cameron