[leggomylibro]

Isn't the Earth sort of a people tank, though?

It's pretty big, but there are only so many variations on "tree", "mountain", "valley", "cave", "swimmy thing", "flying thing", "walking thing", etc etc.

It's not like you can ever expect to walk over the next hill and see an octo-monkey spiraling across the veldt.

[save_ferris]

Seems like a real stretch to compare a 5 gallon tank with one fish and one plant to an entire planet with diverse plant and animal life, biomes, geography, etc.

Sure, there’s a finite number of species that exist, but scientists discover new species fairly regularly. You never know if you’ll walk over the next hill and discover a new bird species. Try doing that in a small tank with one other multicellular organism.