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

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

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They say space is the final frontier, but what if it's just the beginning of our

explorations and experimentation, and what if some experiments require entire galaxies to

conduct them?

We often speculate about alien life and alien civilizations on this show, and we take only

three things for granted about their behavior.

First, that they evolved someplace where nature was as cutthroat as our own world, and thus they

are not wimps, but are out of the product of eons of survival and adaptation, that they rose

to the top of their war

to dominate as we have, and that they made it out in space they first did so by climbing to the

top of a pile of skulls, billions of years deep. Second, we assume they must have a strong

survival urge to have done this, and thus care about their own survival more than that of other

civilizations.

This might vary from a deep willingness to sacrifice for their tribe or hive to utter

personal selfishness, no friend or family ties, and it might vary from a species that would

risk its own neck to help other species to one that would go a million light years out of the

way just to incinerate another species' homeworld, but they will care more about their own survival than ours,

for instance. And third, they will assume anyone in the encounter out in the galaxy will be

...