Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

Everybody at the Galactic Council love the ambassador from the mushroom planet.

He was a real fun guy.

Sometime around half a billion years ago, the earliest animals crawled out of the sea

onto the continents, and yet fungi likely already had arrived on land by then.

We believe it might have been the majority of biomass up there for a time, with giant mushroom

forest possibly being what early animal life on land first flourished in.

Science fiction, and even serious speculation, tend to show us alien life akin to our own.

Often so humanoid, it looks like you just slap some body paint and cosmetic prosthetics on someone.

When trying for more alien appearances, we tend to use prior examples drawn from ancient

life on Earth. We think fungus has been around for a billion and a half years, and is

neither animal or plant, but has some members with characteristics of both and neither,

so it seems reasonable to consider if fungus might be a more common origin of advanced

life. Now until fairly recently, we tend to classify things as plants and animals, or flora

and fauna, and then other stuff, and at the moment we divide other stuff, at least other

stuff that's your periodic, which is to say it has a nucleus,

into a third kingdom of protista, that derives from the Latin for forest and does include

a lot of evolutionary chains that predate animals and plants.

But we might as well say it translates as miscellaneous, as it was the dumping ground

...