#102 – Tom Moynihan on why prior generations missed some of the biggest priorities of all

It can be tough to get people to truly care about reducing existential risks today. But spare a thought for the longtermist of the 17th century: they were surrounded by people who thought extinction was literally impossible.
Today’s guest Tom Moynihan, intellectual historian and author of the book X-Risk: How Humanity Discovered Its Own Extinction, says that until the 18th century, almost everyone — including early atheists — couldn’t imagine that humanity or life could simply disappear because of an act of nature.
This is largely because of the prevalence of the ‘principle of plenitude’, which Tom defines as saying:
This has the implication that if humanity ever disappeared for some reason, then it would have to reappear. So why would you ever worry about extinction?
Here are 4 more commonly held beliefs from generations past that Tom shares in the interview:
- All regions of matter that can be populated will be populated: In other words, there are aliens on every planet, because it would be a massive waste of real estate if all of them were just inorganic masses, where nothing interesting was going on. This also led to the idea that if you dug deep into the Earth, you’d potentially find thriving societies.
- Aliens were human-like, and shared the same values as us: they would have the same moral beliefs, and the same aesthetic beliefs. The idea that aliens might be very different from us only arrived in the 20th century.
- Fossils were rocks that had gotten a bit too big for their britches and were trying to act like animals: they couldn’t actually move, so becoming an imprint of an animal was the next best thing.
- All future generations were contained in miniature form, Russian-doll style, in the sperm of the first man: preformation was the idea that within the ovule or the sperm of an animal is contained its offspring in miniature form, and the French philosopher Malebranche said, well, if one is contained in the other one, then surely that goes on forever.



















